Air Conditioning

INTRODUCTION

An operation and maintenance manual usually includes such items like starting
and shut down sequences, equipment maintenance, etc. However, what is often
missed is the communication of the design intent of the Engineer/Consultant,
to the operating personnel. There had been instances of improper plant
operation, because the operating personnel had not been made aware of how
the systems were designed to operate. This Manual has been prepared to
eliminate such deficiencies.

Further, Air Conditioning and refrigeration Engineering is a specialised line-
from the design stage to the ultimate service operations. It calls for detailed
application design, system and component selection, special care in
installation, commissioning and ultimately the day to day operation of the
Plant, its maintenance and trouble shooting. However well the plant has been
designed and installed, the full benefit of the Plant can only be obtained by
diligent operation and systematic maintenance.

In Central Air Conditioning systems-each Plant is tailor made to a great extent
to suit the job details and meet the maximum load conditions that can be
envisaged during the course of a year and also another special features that
may be required for a particular application. However, since the principle of
working, of the systems are practically same for the various applications, this
Operation and Maintenance Manual will be useful for all types of applications.

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DESIGN DETAIL

Areas Air Conditioned (i) Sq. mtr.
(ii) Sq. mtr.
(iii) Sq. mtr.

Design conditions

Summer Winter Monsoon
DB WB RH DB WB RH DB WB RH
Outdoor
Indoor


Internal Load :
No. of people :
Lighting load :
Equipment load :
Condenser water (inlet) Temp :
Condenser water temp range :
Compressor Sat. Suction Temp. :
Total plant capacity required (Tons) :
Total installed capacity (tons) :
No. of plants to be operated at maximum load
conditions
:
No. of standby plants: :
Refrigeration plants :
Condenser water pump :
Chilled water pump :
*
Type of Plant :
Cooling coil : Direct Expansion
type.
Chilled
water type

Condensing unit : Water cooled. Air cooled.

Chiller : Direct Expansion
type

* Strike out those not applicable.



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PLANT DETAIL

EQUIPMENT MAKE TYPE/MODEL/
ENCLOSURE
HP/NOM.
CAPACITY
QTY.
Compressor
Compressor motor
Condenser
Chiller
Cooling tower
Cond. water pump
Chilled water pump
Cond. water pump motor
Chilled water pump motor
Cooling tower fan motor

Air Handling Units :

Size
Quantity
Motor HP
Filters - Qty
510 x 510 x 50

635 x 405 x 50
635 x 510 x 50

E lectrical Panel




Compressor
Condenser
Evaporator Fresh Air Humidifica-
tion
Remark
Switch/Fuse
starter ra ting
O/L, U/V SPP
V/A meter S.S.



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GENERAL DESCRIPTION OF AIR CONDITIONING SYSTEMS


The term ‘Air Conditioning’ encompasses both cooling and heating. But,
heating will be needed only to a very limited geographical areas in our Country
and hence, this Manual deals with the cooling aspect of the Air Conditioning
Plant.

The Air Conditioning Plant is basically a heat exchange equipment. It takes
away the heat from the area/substance to the cooled and the heat thus taken is
rejected into the atmosphere. That is to say, there is heat exchange taking place
in removing the heat from the area to be cooled and again in rejecting the heat
to the atmosphere. The component of the plant, which removes heat from the
area to be cooled and dehumidified, is the EVAPORATOR along with the air
handling apparatus and air distribution network. The component through
which the heat is rejected to the atmosphere is the CONDENSER. In the air
cooled system, the heat is rejected from the Condenser Coil to the atmosphere
by maintaining a continuous flow of atmospheric air over the Condenser Coil
for which, therefore, condenser fans are necessary. In the Water Cooled
System, the heat is rejected to the atmosphere through the condenser and the
COOLING TOWER. Water pump/pumps is/.are used for circulating the
cooling water through the condenser and cooling tower.

There must be a medium to absorb the heat at the evaporator (i.e. At the low
temperature level) and to reject this heat to the atmosphere. This medium is
called the Refrigerant, which is a volatile liquid having a low boiling point.
The refrigerant is fed into the evaporator in the liquid form at low pressure and
temperature, where in absorbing heat, it changes to its vapour state. To move
the heat laden refrigerant gas from the evaporator to the condenser (where the
heat is rejected to the atmosphere) and also to raise its pressure so that the
gaseous refrigerant can be converted to its liquid state (for reuse in the
evaporator), the COMPRESSOR is used. The refrigerant is at high pressure in
the Condenser, while in the evaporator it has to be at low pressure to enable to
absorb the heat at the low temperature level. For reducing the pressure of the
refrigerant from the high side to that of the low side and also to automatically
monitor the rate of flow of the refrigerant to meet the load requirements, we
have the THERMOSTATIC EXPANSION VALVE. In addition to the above
main components, there are the safety and operating controls and other
ancillaries to complete the system.

It will be evident that the Air-conditioning system consists of a number of
components selected and connected together. For satisfactory performance of
the plant, naturally, the performance characteristics of each of the components
should match well with that of the whole system capacity., Therefore, the
selection (application engineering) of the various components for each
application, has to be done in an exhaustive manner. It is here that the
high degree of experience and expertise of D.O.T. Electrical Wing plays a
major role.

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DIRECT EXPANSION SYSTEM :

The air from the space to be cooled is circulated over the evaporator coil,
inside which the refrigerant is boiling and absorbing the heat from air. The
Evaporator Coil is fitted in the air handling unit which is located in the air
handling unit room and air is distributed to the area to be cooled by a network
of ducts. The Compressor-Condenser set (called the Condensing unit) is
located in a separate plant room. The two components of the refrigeration plant
i.e. the Condensing Unit and evaporator coil are interconnected by means of
the refrigerant piping.

SUPPLY AIR DUCT
AIR FILTER
EVAPORATOR COIL
FAN
SECTION
A.H.U. ROOM
RETURN AIR DUCT OR PASSAGE
MAKE UP & QUICK FILL
CONNECTION
DRAIN
PLANT ROOM
FRESH AIR DUCT
WITH DAMPER
R.A. DIFFUSER
S.A. DIFFUSER
AIR-CONDITIONED ROOM
THERMOSTATIC
EXPANSION
VALVE
LIQUID LINE
STRAINER
COND. WATER
PUMP
COND.
DX SYSTEM




CHILLED WATER SYSTEM :

The Air-conditioning plant engineered and installed for you has the Chilled
Water System. Water is chilled in a Central Composite Refrigeration Plant and
the chilled water is circulated through the cooling coils in air handling units
located in various places or zones of the building. This system is adopted for
multi-story/large buildings, as it is not advisable and economical to run long
lengths of refrigerant piping from the condensing unit (Compressor-condenser
assembly) to the various evaporator coils located in different parts or zones of
the building. Further, this system will be more suited to take care of diversities
in load, inherent in large buildings.

Schematic representation of the system is given on page 7 .


CONTROLS :

There are two categories of controls :-

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(a) Safety Controls to protect the system as under :-

HP/LP CUTOUT :

This stops the compressor either when the discharge pressure exceeds a
set safety point or when the suction pressure falls below a certain set
point.

OVER LOAD RELAYS :

To stop the motor when the current exceeds the rated full load current.

OIL SAFETY SWITCH :

To stop the compressor whenever the oil pressure does not develop as
required.

ANTI-FREEZE THERMOSTAT :

Provided in the outlet of the chiller to protect the chiller against freeze-
up. It stops the compressor in chilled water system, when the leaving
water temperature falls below 38
0
F.

(b) Operating Controls :

These vary according to the requirement of each job. In large size
plants (say at capacities of 40 tones and above) the compressors are
provided with capacity control to unload cylinder when the load drops
down. These are automatic devices which load and unload the
cylinders according to load variations. Provision of the capacity
controls also helps in unloaded starting of the plant, thereby reducing
the heavy draw of current of the compressor motor at the time of
starting.

CRANK CASE ELECTRIC HEATERS :

These heaters are provided in the Crank Case of the compressor to
keep the oil warm when the compressor is idle. The special
refrigeration oil used in the Compressors have a tendency to absorb
refrigerant gas when oil temperature falls down. Absorption of
refrigerant gas dilutes the oil and the lubricating property of the oil will
be substantially reduced; this will affect the bearing life of the
compressor. The crank case heater warm up the oil and reduces the
absorption of refrigerant gas during the idle period of the compressor.
The heater is connected in such a way that it comes ‘ON’ automatically
as soon as the compressor is stopped/stops.

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SUPPLY AIR DUCT
AIR FILTER
EVAPORATO
R COIL
FAN
SECTION
A.H.U. ROOM
RETURN AIR DUCT
OR PASSAGE
AIR-CONDITIONED ROOM
SUPPLY AIR DUCT
AIR FILTER
EVAPORATOR COIL
FAN
SECTION
A.H.U. ROOM
RETURN AIR DUCT OR PASSAGE
AIR-CONDITIONED ROOM
SUPPLY AIR DUCT
AIR FILTER
EVAPORATO
R COIL
FAN
SECTION
A.H.U. ROOM
RETURN AIR DUCT
OR PASSAGE
AIR-CONDITIONED ROOM
SUPPLY AIR DUCT
AIR FILTER
EVAPORATO
R COIL
FAN
SECTION
A.H.U. ROOM
RETURN AIR DUCT
OR PASSAGE
AIR-CONDITIONED ROOM
SUPPLY AIR DUCT
AIR FILTER
EVAPORATO
R COIL
FAN
SECTION
A.H.U. ROOM
RETURN AIR DUCT
OR PASSAGE
AIR-CONDITIONED ROOM
DRAIN
PLANT ROOM
COND. WATER
PUMP
COND.



CHILLED WATER SYSTEM


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COMPRESSOR OIL :

The refrigeration oil used in compressors is a speciality item, to
withstand the changes in temperature conditions in the system.

The Air Conditioning Plant being a heat exchange equipment, its
efficiency and the capacity it can deliver naturally will depend upon the
efficiency of the heat exchanging components, i.e., the evaporator and
condenser and also the efficiency of the compressor which maintains
the required flow rate and pressure for condensation of the refrigerant.
In the case of water cooled plants, since this heat is ultimately rejected
to the atmosphere through the cooling tower (again a heat exchanger)
the performance of the complete plant will be linked with the
efficiency of the cooling tower and the condenser water circulation
system.

Therefore, to get the maximum output of the plant, the various
components mentioned above have to be kept in good condition and
thus maintenance plays a very important role. Maintenance is detailed
in the subsequent chapters.




























OPERATION OF THE PLANT
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This chapter deals with the day to day operation of the plant. Operation of the
plant is not just starting and stopping the plant, but also includes some routine
maintenance work- on a day to day weekly and short period basis.

The result of faulty operation (including the routine maintenance) may escape
the attention, because it is not as dramatic as a breakdown, but in the long run
can work out to be quite costly. Therefore, proper operation is an important
aspect.

There may be symptoms of some minor malfunction, which may appear to be
small or insignificant; yet such small things can grow into major troubles in
course of time; resulting in costly and time-consuming repairs, loss of time,
dislocation and lots of extra work, usually at a most inconvenient time. So the
operating personnel should be sharp in detecting any minor defects and should
take timely action to prevent such minor defects grow into serious problems.

In an air conditioning plant, pressure, temperature, current etc. can never be
constant. These readings vary according to such factors as outside conditions,
room load, etc. The readings can vary during the course of a day itself.

Quite often it is assumed that as long as the temperature in the conditioned
area is within design limits, there is nothing wrong with the plant. But this is a
wrong assumption, because even a slightly inefficient plant can give
satisfactory inside-conditions if the load is less or outside-conditions are
comparatively low. It is the reading of the various temperatures and pressures
of the plant which can lead us to a positive conclusion about the conditions of
the plant. Therefore, one of the important aspects of operation is the logging of
the various readings (log sheet formats are given at the end of this chapter).
Needless to point out that readings should be taken correctly and the operating
personnel should have the ability to analyse the readings to establish whether
the plant is working satisfactorily or not.

OPERATING INSTRUCTIONS :

Before starting the Plant :

1. Ensure all dampers in air ducts are open.,

2. Ensure all valves in the

(a) Refrigeration Systems,

(b) Condenser Water Lines, and

(c) Chilled Water Linesare open, except those of the standby items
of equipment.

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10
3. Check up water level in the cooling tower and ensure that the make up
water system is working satisfactorily-such as float ball is OK and float
valve is free in movement and there is water flow when the ball is
pressed down, etc., and there is regular make up water supply to
cooling tower.

During operation, some water is lost by way of evaporation and drift
losses. Unless these losses are made up continuously, the water level in
the cooling tower will fall down and the condenser will not get full and
continuous water flow thus affecting the plant; the discharge pressure
will shoot up and the plant will stop on High Pressure cut out switch.

4. In chilled water plants, check the water level in the expansion tank and
ensure that the make up water system is working and there is regular
water supply.

Water level in the chilled water system can fall down due to pump
gland drips. If the level in the expansion tank is not maintained, air can
enter the chilled water system affecting the system performance
substantially and can even lead to freeze up of the chiller.

5. Check all air filters and water strainers and clean whenever found dirty.

6. Ensure that all doors and windows of the air conditioned area are
closed.

7. Ensure that the crank Case of the Compressor is warm to the physical
touch. If it is not warm, check for defects in the Crank Case
heater/circuit. Do not start the compressor until the defect is rectified
and the Crank Case warms up. Otherwise, poor lubrication will result,
reducing the life of the bearings of the Compressor substantially.

8. Check supply voltage. It should be within 400 to 440 volts. If the
voltage is less than 390 volts, do no start the Plant. The windings of the
motors can get affected if run on low voltage conditions.

STARTING SEQUENCE IMPORTANCE/SIGNIFICANCE OF
OPERATIONAL STEPS
1. Switch ‘ON’ the mains Observe the voltage. If it is less than 380
volts, DO NOT START the plant.
2. Start
2.1 Air handling unit motors
2.2 Condenser water pump/s. Check
that sufficient water pressure is
built up.
Correct pressure of the condenser water
system: the water pressure built by the
condenser water pumps (i.e. The
difference between the discharge and
suction pressures of the pump) will
depend upon the total length of the water
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pipes in the system, number of water
passes provided in the condenser etc. The
pressure observed at the time of
commissioning and handling over the
plant should be the best guide.
As a general guidance, the pressure built
up by the pump will be around 1.75 to
2.46 kg/cm
2
(25 to 35 PSI).

2.3 Cooling tower fan/s Inspect the cooling tower fan guard/s
periodically and ensure that they are in
good condition.

2.4 Chilled water pump/s - where
chilled water systems are
installed. Confirm that sufficient
pressure is built up by the
pump/s.
Correct pressure of the chilled water, the
pressure built by the chilled water pump/s
will depend upon the length of piping,
fittings, chiller, etc. Here again the
pressure observed at the time of handing
over the plant is the best guide.

2.5 Switch ‘ON’ the compressor
control switch.
The compressor control circuit is
protected by a fuse and a switch is
provided for service purpose.

2.6 Switch ‘ON’ the refrigerant
solenoid valve or the pilot
solenoid valve (whichever is
used).
Refrigerant solenoid valves are provided
in the main liquid line usually where the
plant size is small. Pilot solenoid valves
are generally provided for bigger plants.

2.7 Start the compressor motor. In
the case of slip ring motors,
stator-rotor starters are used.
After switching on the stator
switch of the starter, turn the
Rotor Wheel or handle
gradually and move smoothly to
the full running position.
Caution : The movement of
Rotor Wheel/Handle should be
neither too fast nor too slow.
Never leave the wheel/handle in
an intermediate position.
The rotor circuit in a slip ring motor
starter is provided with number of
resistances. At the point of starting,
maximum amount of resistance is in
series with the rotor and as the rotor
wheel is turned towards the full speed
(run) position, the resistances are
progressively cut off and rotor windings
get connected in Star.
If the rotor wheel is kept in an
intermediate position, the resistance wires
in the rotor starter can get burnt.
3.1 As the compressor is started the
compressor oil pressure should
build up. Check that correct net
oil pressure is build up. Once
the oil pressure is built up, the
cylinders of the compressor will
Since the oil in the Crank Case of the
Compressor is subjected to the suction
pressure, the NET OIL PRESSURE
developed by the (compressor) oil pump
is the difference between the reading
shown on the oil pressure gauge and the
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load up. suction pressure at the time of taking the
reading. For example :

If the oil pressure gauge reading is 110
PSIG (7.73 kg/cm
2
) and the suction
pressure at that time is 70 PSIG
(4.92kg/cm
2
) the NET OIL PRESSURE
is : 7.73-4,.92 = 2.81 kg/cm
2
(110-70 = 40
PSI).

It is the NET OIL PRESSURE which
supplies sufficient lubrication to the
bearings and loading mechanism.

Suction pressure of the system can be
varying according to the load conditions
and consequently the reading shown by
the oil pressure gauge also will be
varying. Hence to ensure that the
compressor lubrication system is working
satisfactorily one has to arrive at the NET
OIL PRESSURE every time.

The net oil pressure should be around 2.8
kg/cm
2
(40 PSI).

3.2 Check the oil level in the oil
sight glass of the compressor.
The oil level should be 3/8 or
3/8 of 1/2 the sight glass.
The oil level in the compressor oil sight
glass should be within 3/8 to 1/2 of the
glass.

In operation, certain amount of oil gets
entrained in the refrigerant vapour in the
compressor and is carried away to the
system alongwith the refrigerant. It is
obvious that the oil carried into the
system should return to the compressor,
continuously and automatically, to
maintain sufficient oil level in the
compressor. While designing the system
and the refrigerant piping, it is ensured
that the oil return will be proper.
However, due to certain malfunctions of
the system that can develop due to
improper maintenance or shortage of
refrigerant in the system due to leakage,
etc., The oil return can get affected.
Hence, it is important to observe the oil
level in the compressor periodically. If the
oil level tends to go down, it is a sure
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13
indication of a system malfunction.
Immediate action should be taken to find
the reason for the improper oil and rectify
the defect. Otherwise a major compressor
breakdown can occur, resulting in costly
and time consuming repairs.

4. After the plant operation has
stabilized, check all the
pressures and temperatures and
ensure that the plant is working
satisfactorily.
Correct temperatures and pressures.

It may take about half hour for the plant
to stabilize on starters. Readings are to be
taken (and received) after the plant has
stabilized.

It should be noted that the temperatures
and pressures will vary according to
various factors. Therefore, there is
nothing like a constant reading for all
parameters. Judgment is needed to
analyse the readings and to conclude the
performance of the plant. Some broad
guidelines are given below to analyse the
readings. It should be noted that these are
to be taken only as a general guideline.

(a) Discharge Pressure : This depends
mainly on the temperature of the
condensing medium (i.e. Water or
air) and to some extent on suction
pressure. Once the system has
stabilized and the load is within
limits, the discharge pressure is
primarily governed by the
temperature of the condensing
medium.
In water cooled condensers generally
the condensing temperature of the
refrigerant in the condenser (i.e. the
saturation temperature corresponding
to the discharge pressure) will be 10
0
C to 11.1
0
C (18
0
F to 20
0
F) above
the entering water temperature to the
condenser (or) about 5.50C (100F)
above the condenser water outlet
temperature. For example:
Inlet water temperature to
condenser: 850F. Then the
condensing temperature should be
bout 39.4
0
C (103
0
F) which is about
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14
14.5 kg/cm
2
(207 PSI).

(b) Again the inlet water temperature is
governed by the outside WET BULB
Temperature. In atmospheric type
cooling towers, the water temperature
can be brought to about 4.4
0
C to
5.5
0
C (8
0
F to 10
0
F) of wet bulb i.e.
Outside WB + 8 to 10
0
F and in
induced draft cooling towers the
water temperature can be outside WB
+ 2.7
0
C to 3.3
0
C (5
0
F to 6
0
F).

(c) Cooling tower performance also can
be judged by the relations between
outside W.B. Temperature and
cooling tower sump temperature (this
difference is called the ‘wet bulb
approach’ of the cooling tower.

(d) The air cooled condenser- the
condensing temperature will be about
16.7
0
C to 19.4
0
C (30
0
F to 35
0
F)
above the outside DRY BULB
temperature.

Note that in water cooled unit the
condensing temperature is governed
by the outside WET BULB
temperature, while in air cooled units
it is the outside DRY BULB
temperature that has to be taken as
guide line.

(e) Suction pressure : It is governed by
the load on the plant or in short the
temperature in the condition area (+)
outside conditions. Once the room
temperature has fairly stabilized, the
correctness of the suction pressure
can be verified by the canvas
connection temperature i.e. the
temperature of air coming out of the
air handling unit. The saturation
temperature of refrigerant
(corresponding to suction pressure)
should be about 8.3
0
C to 10
0
C (15
0
F
to 18
0
F) below the canvas correcting
temperature.
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15

Refrigerant R-22 saturation
temperature - pressure chart is given
at the end of this chapter.

As the plant is started, the room
temperature will gradually fall down
and so also the suction pressure.

(f) Oil pressure : It is the NET OIL
PRESSURE developed by the oil
pump that is important. The net oil
pressure should be 2.8 kg/cm
2
(40
PSI) more than the suction pressure.

(g) The pressure developed by the
condenser and chilled water pumps,
as already explained earlier, will
depend on the length of the water
circuits etc., and since these pressures
cannot change for a particular
system, the pressures observed at the
time of handing over should be the
best guide.

5. Record hourly readings of
temperature, pressures, current
and other data in the log sheet.
Sample log sheet format is
given at the end of this chapter.
It is very important to take the various
readings correctly and record them in the
log sheet. These log readings help in
analysing variation of readings on a day
to day basis and to establish the condition
of the plant. When a problem arises with
the plant, the log readings of earlier days
or corresponding days in the previous
years, will help to lead us to the problem
area. Therefore, the readings should be
taken faithfully and the log book kept in
good condition.
6. Check for any unusual
noise/vibration in the plant. If
any is noticed, trace out the
reason for this and rectify. If
you are not able to identify the
cause of any vibration/noise,
contact maintenance. Agency /
manufacturer immediately.


7. During the operation of the
Plant, if it stops suddenly, try to
trace out the reasons for this to
Whenever a plant suddenly stops, it is the
general practice of operating personnel to
first reset the oil safety switch and try
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16
happen, before starting the plant
again. If on restarting, the plant
trips again, please get in touch
with maintenanca agency /
manufacturer immediately.
starting the plant. This is a wrong
procedure. Resetting of oil safety switch
should be the last item in the step by step
procedure in finding the reasons for the
sudden stoppage. The plant could have
stopped on the pressure switches, water
flow switches, antifreeze thermostat,
motor overload, etc. First check these. If
ultimately it is found that all these are OK
then try resetting the oil switch. If it is
established that the plant has tripped on
the oil safety switch, then a very close
watch on the oil pressure (net oil
pressure) is absolutely essential. If the net
oil pressure tends to go down it is sure
indication of a problem in compressor.
Immediately trace out the problem and
rectify. Otherwise, a major compressor
breakdown can occur. If in difficulty,
contact maintenance agency.


STOPPING SEQUENCE IMPORTANCE/SIGNIFICANCE OF
OPERATIONAL STEPS
1. Switch off the refrigerant
solenoid valve. Compressor will
go off on the low pressure section
as the system gets pumped down.


2.1 Switch off the compressor mains.


2.2 Check that the Crank Case
electric heater comes on as soon
as compressor stops and heater is
working.
The importance of the Crank Case electric
heater has been explained in detail, in
chapter 3. Ensure that the Crank Case
heater comes ‘ON’ when the compressor
is stopped.

3. Stop chilled water pump/s.
4. Stop air handling unit/s.


5. Stop condenser water pump/s and
cooling tower fan/s.


SOME IMPORTANT POINTS TO BE TAKEN CARE OF :

1. Where standby plant/s, pump/s etc. are provided systematically change over
the work of the plants periodically say once in a week or even every day. This
will ensure uniform wear and tear of the plants. Further this also helps in
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17
ensuring that all the plants are in good repair and the standby is in good
condition should a necessity occur.

2. Never ‘SWITCH OFF’ the main switch on the main electrical board or switch
off any component of the system, when the plant is in operation, for ease in
shutting down the plant. There had been instances of operators doing this way.
Such an action will put a heavy strain on the isolating switch/es and they can
even get completely damaged.

3. All the water valves in the system can be kept open all the time and need not
be closed daily. But it is essential to close and open each valve periodically to
ensure that the valves work and do not get stuck by scale formation or dirt
accumulation.

4. Keep the plant room clean. Do not use the plant room, particularly the air
handling unit rooms, as lumber rooms.
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SPECIMEN LOG SHEET FOR TEMPERATURE READINGS
DATE :
TIME AHU-1 AHU-2 Outside Temp Inside Temp Inside Temp Remarks
CANVAS RETURN CANVAS RETURN
DB WB DB WB RH DB WB DB WB RH DB WB RH DB WB RH DB WB RH






















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SPECIMEN LOG SHEET FOR PLAT ROOM READINGS
(CHILLED WATER PLANT)
TIME
COMP-1 COMP-2 CHILLER-1 CHILLER-2 COND-1 COND-2
CH. W.
PUMP 1
CH. W.
PUMP 2
COND
PUMP 1
COND
PUMP 2
C.T.
FAN
S
.
P
.
D
.
P
.
O
.
P
.
A
m
p
s
.
S
.
P
.
D
.
P
.
O
.
P
.
A
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DATE:

R. Sharma (BSNL Electrical Zone Patna)

20

MAINTENANCE


DAY TO DAY MAINTENANCE :

It is a well known fact that all mechanical equipments need systematic
maintenance. In the case of Air-conditioning plant this aspect assumes greater
importance. Unless the work of maintenance is carried out in a planned
manner needless to point out that the full capacity of the plant not be obtained.
Further by proper maintenance work major-break down of the plant can be
substantially reduced.

It has been explained in the Chapter-3 that an Air-conditioning plant is a heat
exchange equipment. So to get the bast out of the plant, the heat exchangers
should be kept in good condition in addition to the maintenance work required
for any Electro-Mechanical equipment.

Maintenance pertaining to the Air-conditioning plant falls into two-categories.

1. Running/operating maintenance, and

2. Planned and preventive maintenance on a periodical basis.

While the operating maintenance, being simple to be carried out by the
operating personnel of the plant, the second category of work calls for
expertise handling, thus calling for the services of a experienced Mechanic.
For bigger plants, service engineers will be needed.

This chapter deals with the step by step running/operating maintenance

DAILY :

1. WATER LEVEL IN COOLING TOWER :

Check water level before starting the plant. Also ensure that the make-
up water system is working properly i.e. the float valve is working
satisfactorily and there is sufficient water in the make-up water tank for
the full day operation of the plant. As explained in Chapter 4, if this
step is not taken care of, the plant performance will be affected and the
compressor can stop on the High Pressure Switch.

2. IN CHILLED WATER SYSTEM :
Check up water level in the expansion tank and ensure the make-up
water system is working satisfactorily. If this is not ensured, there are
chances of the freeze up of the chiller.


3. CHECK CRANK CASE HEATER :
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21

It is very important that the crank case heater comes on automatically
when the compressor is stopped. This has to be checked on a day to
day basis without fail. Do not start the compressor, unless the crank
case is warm to the physical touch.

The necessity of the crank case heater coming into operation during the
idle period of the compressor has been explained in Chapter 3.

4. OIL LEVEL IN COMPRESSOR :

This should be within 3/8 to 1/2 of the oil sight glass. If this level is not
maintained, it is a positive indication of a malfunction in the plant. If
the operating personnel cannot locate and rectify the problem, service
personnel should be informed immediately.

CAUTION :

If the oil level in compressor goes down, NEVER FILL IN OIL to
make up the level. The only correct step is to find out the reason/s for
the poor oil return and rectify it.

5. Be alert to look for/observe unusual noise/vibration than normal. Even
if a small vibration sets in than normal, look for the reason and rectify,
rather than leaving it as negligible.

6. LOG BOOK :

It may appear as a bit odd to talk about logging readings as a
maintenance step. But, remember that, it is the readings that tell the
real condition of the plant. If the readings show any abnormality, there
is some malfunctioning somewhere and this has to be investigated and
rectified without delay to avoid a major breakdown. This log book
forms an important maintenance tool for day to day operation of the
plant, as well as for future reference.

7. Check for over heating of any part in the plant.

WEEKLY :

1. CLEAN AIR FILTERS :

A dirty air filter can reduce plant capacity. More the dirt accumulation
on the air filter, greater will be the reduction in capacity of the plant.
Air filters, if not cleaned regularly will get saturated with dirt and
thereafter dirt will pass on to the cooling coil fins, which will affect
plant capacity much more and in extreme cases can even lead to liquid
flood back to the compressor, which is highly injurious to the
compressor. Cooling coils being wet, this dirt/dust will form a crust in
R. Sharma (BSNL Electrical Zone Patna)

22
the coil. Hence, air filters are to be cleaned regularly. Weekly cleaning
has been suggested here. But where plants are installed in dusty
environments, it may be necessary to clean the air filters more often.
For example after a dust storm in Northern India, it is a must to clean
the air filters.

Air filters should be changed, when it is found that cleaning does not
remove all the dust.

2. LEAK TESTING FOR REFRIGERANT LEAK :

A halide torch should be used, as this is a sensitive service tool to
locate even minor leak. While leak testing, the approach should be to
find a leak rather than taking it for granted that there won’t be any leak
and doing the work of leak test as a virtual.

A leakage-even a minor one- can lead to lot of problems, such as poor
oil return, heating of compressor apart from poor cooling, etc. Further,
Refrigerant is a costly item and so less leak becomes a big cost saving
centre in the operation of the plant.

3. WATER PUMP GLANDS :

Check for excessive water leak through the gland (certain amount of
water drip through the gland is necessary to keep the gland cool).
However if the drip develops into a regular flow, it is an indication that
the gland is not holding well. The gland nuts can be tightened to reduce
the leak. When tightening the nuts does not improve the situation, the
gland packing has to be renewed. If this is not done in time, water
consumption will go up and in chilled water pump, a water leak means,
loss of refrigeration.

The gland nuts should be tightened evenly to avoid the gland flange
touching the shaft. Always check for heating of the gland after
tightening. If the gland gets heated, it is an indication of overtightening
of the nuts.

4. Clean water strainers wherever provided. A clogged strainer reduces
water flow rate and thus affect the plant performance. Further, if the
strainers are not cleaned regularly, the dirty muck will form a crust and
it becomes too difficult to clean. This can even puncture the strainer
mesh, necessitating replacement of the strainer element.

Though the strainer appear to be small item in a complete plant,
remember that they play a very important role in keeping the heat
exchange surfaces clean and efficient.

5. BELT TENSION OF BELT DRIVES :

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23
Check the tension of belts and tighten whenever found loose. A loose
belt will reduce transmission efficiency and its own life will be
reduced; further the drive pulleys can get heated up. Replace belt when
it is not possible to tighten them any further. In mullet-belt drives,
change the complete set of belts. Select the belts for a matched set. If
this is not done, the load will be taken only by the smaller length belts,
thereby affecting transmission efficiency and belt life.

6. It is the pressure gauges and thermometers which give us a correct
indication of the plant performance and condition. Therefore, ensure
that these are in good order.

7. Check the spray of the cooling tower nozzles.

8. Drain, clean and refill the cooling tower sump. Cooling towers, being
in the open, collect lot of dust and muck, hence it is necessary to clean
once in a week.

Analyse the pressure and temperature readings of the plant from the log
book and establish that the plant is working satisfactorily. Corrective
action should be taken promptly when readings show even a minor
malfunction

PREVENTIVE MAINTENANCE :

As the name implies, Preventive Maintenance is a planned service programme.
This helps in minimizing major breakdown, to operate the plant at design
efficiency and also to save energy. As explained in Chapter 5, this
maintenance work calls for the services of a well experienced
Serviceman/Service Engineer.

A step by step procedure in this regard in given below as a guideline :-

MAINTENANCE FREQUENCY
1. Periodical Inspection and service
1.1 Check the various pressures, temperature and
the current drawn by the motors. Analyse the
readings to ascertain the condition of the plant.
Quarterly (once in 3
months)
1.2 On analysing the readings, if some
malfunctioning is indicated, investigate and
rectify the faults.

1.3 Ensure that oil return is proper.
1.4 Check crank case heater for proper operation.
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24
1.5 Carry out a through test for refrigerant leak, by
halide torch.

1.6 Inspect the condition of the air filters. Replace
them if they are found to be beyond
cleaning/sagging-out of shape .

1.7 Check operation of all safety and operating
controls.

1.8 Check belt tension and adjust. Replace worn out
belts (in sets only).

1.9 Check alignment of all belt and direct drives
and rectify where found necessary. Dial gauge
should be used to check the alignment of direct
drive in Compressors.

1.10 Inspect the cooling tower for proper operation
and ensure that the ‘wet bulb approach’ of the
tower is within limits.

1.11 Check all bearing surfaces for abnormal heating.
Where such symptoms are observed, investigate
and take corrective action.

1.12 Check drains for free flow and clean wherever
necessary.

1.13 Check for abnormal vibration and noise. Check
for tightness of all fastening bolts.

1.14 Check cooling coil fins for dirt accumulation.
Clean if found necessary.

1.15 Check that the electrical connections are tight.
1.16 Using an Electrical blower, blow dust
accumulated within the motor. Dust
accumulation on windings will retard the
cooling of the motor windings and thus affect
the life of the windings.

2. Keep the heat exchange surfaces clean. Half yearly or yearly-Please
see note at the end.
2.1 CONDENSER :
2.1.1 Water cooled condenser. Check the “leaving
temperature difference” (Condensing temp -

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25
Leaving Condenser Water temp.). If it is more
than 6.6
0
to 7
0
C (12 to 12.5
0
F) Condenser Water
tubes will have to be cleaned.
Note : The frequency of cleaning the condenser tubes will depend upon the quality of
water used. When water used is fairly soft, yearly cleaning will be found
satisfactory. The frequency of cleaning will have to be established by
observing the operation over a period of time.
2.1.2 AIR COOLED CONDENSER :
The temperature difference between the
Condensing temperature and outside dry bulb
temperature is the criterion to determine
whether the condenser fins need cleaning. The
temperature difference established at the time of
commissioning and handing over of the plant is
the best guide line.
Water under pressure sprayed over the coil is
the positive method of cleaning a condenser
coil. The (Pressure) water it should be applied
in the opposite direction of the operating
direction of the air flow of the coil. The
frequency of cleaning will depend upon he
installation.
Half yearly of oftener.
2.2 COOLING COIL :
The temperature difference between the canvas
connection temperature and evaporator
temperature is the criterion to determine
whether the coil needs cleaning. The
temperature difference found at the time of
commissioning and handing over the plant is the
best guide. Cooling coils also are to be cleaned
with water under pressure.
Half yearly or oftener.
3. Lubricate all moving parts. The compressor oil
however need be changed only if the condition
of oil is bad.

4. Check and clean contacts in starters/contactors. Half yearly.
Note : Do not dress the Contacts with emery or sand paper. The contacts have hard
wearing coatings. If emery or abrasive paper is used, this coatings may get
removed. The shape of the contact point surfaces are made slightly sloping so
that the moving contact surface slides on the surface of the fixed contact and
maintains a positive contact. Thus the initial points of contact where arcing
occurs on making and breaking (which causes the pitting of the contact
R. Sharma (BSNL Electrical Zone Patna)

26
surfaces) are not the areas through which current passes in operation. These
specially shaped surfaces can get out of proper shape if emery paper is used.
Therefore cleaning should be done only with cloth. Replace badly pitted
contacts.


R. Sharma (BSNL Electrical Zone Patna)

27
TROUBLE SHOOTING

Even with a well maintained and operated plant troubles can develop. When
trouble occurs, a systematic study of all symptoms (by taking temperature and
pressure readings) should be made to come to a conclusion as to the cause of
the trouble.

Many of the breakdowns are caused originally by simple faults. Hence, while
trouble shooting, look for simple points first. Never jump to conclusion from
some symptoms only. Analyse all symptoms and come to a logical conclusion.

A properly maintained log book will help to a great extent to pin point the
probable area of trouble. Breakdown or major malfunctioning generally will
not occur all of a sudden. A small defect will develop into a major one, if not
detected and rectified in time. For example, a very minute gas leak over a
period of time can lead to lot of problems, such as, insufficient cooling, poor
oil return, excessive heating of compressor head etc. If only regular leak test
was taken and the minute leak detected and rectified, all the major troubles
cited could have been avoided.,

A trouble shooting chart is given on the next page as a guide line.


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28

TROUBLE SHOOTING CHART

SYMPTOM OR
DIFFICULTY
POSSIBLE CAUSES REMEDIAL
MEASURES
1. Compressor
refuses to
start
(a) Main switch open Close switch.
(b) Fuse blown Correct the fault and
replace fuse.
(c) Thermal cutout relay open Check and attend electric
supply
(d) Defective contactor Repair or replace.
(e) High pressure cutout open Correct high pressure as in
symptom 4 and reset high
pressure cutout.
(f) Low pressure cutout open Correct low pressure as in
symptom 7 and reset low
pressure cutout.
(g) Oil pressure failure switch
open
Correct low oil pressure as
in symptom 11 and reset
the low oil pressure cutout.
(h) Thermostat set too high Reset thermostat.
(i) Liquid line solenoid not
open
Repair or replace.
(j) Motor Electrical trouble Repair or replace motor.
(k) Loose wiring Check all wire junctions
2. Plant
Vibrating
(a) Foundation bolts not tight
enough, hence vibration
Tighten the bolts.
(b) V belt drives or couplings
gone out of alignment
Align the V belts drives or
couplings as the case may
be.
(c) Pulley/fly wheel loose on the
compressor shaft
Tighten locking nut.
(d) Motor pulley loose Change or adjust motor
pulley.
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29
3. Compressor
noisy
(a) Too high an oil level causing
liquid hammering
Correct the oil level.
(b) Liquid flood back to the
compressor
Check for reasons for
liquid flood back and
rectify.
(c) Excessive wear on bearing Overhaul the compressor.
4. High
Discharge
Pressure
(a) Discharge shut off valves
not fully opened.
Open valve.
(b) Air or non-condensables in
the system
Purge the non-condensable
from the system.
(c) Condenser entering water
temperature high
(I) Inspect cooling tower
spray or water
distribution in
cooling tower. Rectify
defects in the cooling
tower.
(ii) Outside wet bulb
temperature higher
than normal. This
being a natural
phenomena there is no
possible remedy.
However, this occurs
very rarely and if at all
it happens, it would be
only for a short
duration.
(d) Condenser Water tubes
fouled or sealed up. In such
a case the difference
between inlet and outlet
water temperature will be
lower than normal. Also the
LTD will be high. (L.T.D.:
Leaving Temperature
Difference i.e. Condensing
temperature (minus)
condenser water leaving
temperature)
Descale the condenser.
(e) Insufficient water flow
through the condenser. This

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30
will be indicated by a higher
than normal temperature
difference between inlet and
outlet water temperatures of
the condenser. This could be
due to :
(i) Partially opened water
valves .
Open fully.
(ii) Low water level in
cooling tower .
Rectify. Ensure enough
make-up water.
(iii) Blocked water strainers Clean strainers.
(iv) Passages with water
pump impeller blocked.
Open pump, inspect and
clean.
(v) Pump inefficient. Overhaul pump.
(f) System overcharged Remove excess refrigerant
from the system.
5. Low
Discharge
Pressure
(a) Too much cooling water to
the condenser.
Regulate the water supply.
(b) Cooling water exceptionally
cold.
Reduce the water supply.
(c) Compressor running
unloaded.
Refer item 9.
(d) Suction shut off valve not
fully open
Open the valve.
(e) Insufficient refrigerant in
system
Charge the refrigerant after
thorough leak test.
(f) Leaky discharge valve Remove cylinder cover.
Inspect the valve plates
and rings and renew if
necessary.
(g) Low suction pressure See symptom 7 below.
6. High suction
pressure
(a) Excessive load on the plant
than designed
This may be of a
temporary duration.
(b) Too much liquid being fed
through expansion valve.
Adjust the expansion valve
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31
(c) Compressor operating
unloaded
Refer item 9.
(d) Leaky suction valve. Remove the cylinder
covers, inspect valve plates
and rings and renew if
necessary.
7. Low suction
pressure
(a) Liquid line filter dirty. Clean or replace.
(b) Compressor suction strainer
dirty.
Clean or replace.
(c) Expansion valve blocked. Clean expansion valve.
(d) Shortage of refrigerant in the
system.
Charge refrigerant, after
thorough leak test.
(e) Incorrect adjustment of
expansion valve.
Open expansion valve or
readjust to feed more
refrigerant.
(f) Evaporator dirty. Clean.
(g) Compressor not unloading. Check unloading
mechanism.
(h) Discharge pressure low . See symptom 5 above.
(i) Too much oil in the system. Drain the oil gradually
from compressor keeping
an eye on oil return.
8. Compressor
not unloading
(a) Capacity control gone out of
adjustment.
Adjust.
(b) Cut-outs for capacity
automatic control not set
correctly.
Reset the cut-outs of
capacity control.
(c) Rocker arms displaced Check and adjust.
9. Compressor
not loading
(a) Inadequate oil pressure See symptom 11 below.
(b) Unloading mechanism stuck Rectify or replace.
(c) Oil lines or oil strainer of
capacity control dirty .
Clean lines and strainers.
(d) Solenoid valve coil defective Check and replace.
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32
(e) Plunger of solenoid valve
stuck.
Clean .
10. Compressor
loading and
unloading
intervals too
short
(a) Expansion valve in correctly
adjusted .
(b) Oil pressure erratic.
Recheck and set expansion
valve.
Check compressor oil level
stop oil foaming and clean
oil lines.
11. Low oil
pressure
(a) Compressor running I wrong
direction.
Rectify.
(b) Oil strainer dirty . Clean oil strainer.
(c) Oil lines choked. Clean oil lines.
(d) Oil pump not operating
satisfactorily.
Check and repair.
(e) Oil regulating valve gone
out of adjustment.
Adjust or repair oil
regulating valve by
rotating clockwise to
increase pressure.
(f) Bearing clearance too high. Overhaul the Compressor.
12. Compressor
oil level
going own.
(a) Oil trapped in the system. Investigate reasons for
poor oil return and rectify.
(b) Piston rings loose and
leaking.
Renew piston rings and if
necessary the piston.
(c) Worn-out cylinder liners. Replace cylinder liners.
13. Compressor
working
continuously
(a) Lack of refrigerant. Leak test and charge
refrigerant.
(b) Thermostat adjusted low. Readjust.
(c) Compressor delivery valves
leaking.
Inspect the valves renew or
replace.
14. Compressor (a) Cycling on high or low
pressure switches.
Refer items 6 or 7.
(b) Thermostat differential low. Readjust differential.

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33
Note : 1. Before investigating the causes of the symptom or difficulty
experienced, make sure that all pressure gauges and all cutouts are
functioning satisfactorily.

2. The above is only an illustrative list.

3. Wherever necessary refer to Compressor Manual

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34


SOME SPECIAL SERVICE OPERATIONS


PUMPING DOWN

When the plant is to be shut-down for prolonged period or if the refrigeration
system is to be opened out for repairs and overhaul, it is necessary to pump
down all the refrigerant from the Evaporator and piping and store it in the
condenser/receiver. This is called pumping down. Following procedure should
be followed when it is necessary to pump down the refrigerant.

1. Close the liquid outlet valve on the condenser/receiver and start the
compressor. The compressor should be run until the suction pressure
gauge indicates a pressure of 2 psig. The compressor should then be
stopped and discharge/shut-off valve should be quickly closed.

2. To pump down a system it will generally be necessary to operate the
compressor below the normal cutout setting on the low pressure
switch. It will, therefore, be necessary to remove the cover from the
pressure switch and manually block the contacts in close position.
Wherever the refrigeration system is equipped with a magnetic stop
valve, it will be necessary to see that this stop valve is kept open during
the period of pump-down. This may be done by keeping the solenoid
coil energised during the pump down cycle. Certain types of solenoid
valves are equipped with manually operated stems which may be used
to keep the valve open during pumping down.

PUMPING OUT THE REFRIGERANT :

It may sometimes be necessary to remove the entire charge of refrigerant from
the system and store it in another receiver. In that event, first, pump-down the
gas as outlined above. Close compressor suction valve and stop machine. Back
seat the compressor discharge service valve and connect the line from the
empty cylinder to the gauge connection. Place the receiver in an ice water bath,
purge the air from the line and turn slowly the compressor discharge service
valve away from the back seat position. Open the valve on the refrigerant
receiver. Keep the condenser warm by keeping the condenser water pump
running to assist the removal of refrigerant. Wherever a separate compressor is
available, this may be used to pump out the refrigerant from the system into
the empty receiver.

REPLACEMENT OF DEFECTIVE PARTS :

It may be sometimes necessary to open up a closed refrigeration system for
replacement of defective parts. In the event, the system should first be pumped
down as detailed above. Never leave the refrigerant lines open as dirt and
R. Sharma (BSNL Electrical Zone Patna)

35
moisture may settle on the system and causes heavy damage when the plant is
started up.

When reassembling the system, it is advisable that the liquid side should be
closed up. Before completely sealing the system, crack the liquid outlet valve
to purge air from the system. Close the valve immediately and make the final
joint. However, where the system has been kept open for a long time, it is
necessary to evaluate the system before charging gas.

Test the system for leaks with Halide torch. If everything is satisfactory the
compressor may be started in the following way :-

1. Open the compressor suction and discharge valves.

2. Open hot gas inlet valve on the condenser/receiver, if any.

3. Open liquid outlet valve. This will build-up a pressure in the system
and cause the low pressure switch to function and start the compressor.
(Note : If the low pressure switch contacts were kept mechanically
‘closed’ during pump down cycle, this must be removed. Also, if the
liquid solenoid valve was manually opened, it should be reset for
automatic operation).

4. Check oil level in the crank case and the refrigerant charge. If
necessary, add oil and gas. In case of refrigerant shortage, bubbles may
appear on the liquid indicator in the refrigerant liquids line.

REFRIGERANT CHARGING :

If the system has lost refrigerant gas due to leaks, broken connections, etc., this
gas must be replaced in order to ensure proper operation. It is important that no
gas be added until all leaks have been repaired. Shortage of refrigerant may be
indicated by any of the following symptoms :-

1. Distinct hissing sound from the expansion valve.

2. Low suction pressure and low condensing pressure. This condition may
cause ‘short cycling’ of the system.

3. Numerous bubbles at the liquid level indicator on the liquid line.

4. Presence of the oil at leaking joint, connection, bolt and head etc.

To add refrigerant to the system, follow the procedure outlined below :-

1. Back seat the compressor suction shut-off valve. Remove the plug
from the gauge port.

R. Sharma (BSNL Electrical Zone Patna)

36
2. Connect the charging line from the refrigerant drum to the gauge port
but before tightening the connections, ensure that all air is purged from
the line by cracking the outlet valve on the refrigerant drum.

3. Keep the refrigerant drum in a vertical position with the outlet
connection on top so that, only gas can enter the system.

4. Start the compressor. Crack the suction valve off the back seat and
open the refrigerant drum valve. Gas will start flowing into the system.

Charge the system slowly. Stop the charging every two or three
minutes. Allow the system to stabilize and check suction, pressure and
liquid indicator, etc. Repeat this process of charging until system is
fully charged.

5. Watch the liquid level indicator and the suction pressure gauge. When
the bubbles disappear and the suction pressure is normal, close the
drum valve, back seat the compressor suction shut-off valve, remove
the charging line and plug the gauge port.

6. Check the oil level.

Note : Whenever a system is provided with a charging valve in liquid
line, it is recommended that this should be utilised in preference to the
gauge pot on the suction valve.

PURGING OF NON-CONDENSABLE GASES :

A refrigerant system must be kept free from gases other than the refrigerant.
Listed below are several sources of non-condensable in a system :

1. Leakage of air onto a system operating at a vacuum through leaky
joints or on the packing.

2. Residual air in hose connections when adding oil or when charging
refrigerant.

3. System not properly evaluated after the system has been opened out for
repairs.

4. Possible non-condensable in the gas cylinder itself.

(Note : To avoid this, always get refrigerant from well established and
reputed suppliers).

Non-condensable gases will cause high condensing pressures This will reduce
the refrigeration capacity, increase the operating cost and cause erratic
operation of the system. It is necessary therefore that non-condensable gases
must be purged from the system as soon as their presence is evidenced. In
R. Sharma (BSNL Electrical Zone Patna)

37
order to determine whether air is present in the condenser, following procedure
should be followed:

Pump down the unit. Run the condenser water pump for approximately half an
hour to allow the condenser to cool down. Install a pressure gauge on the
discharge service valve. After the water has circulated in the condenser for
sometime, its temperature and the pressure in the condenser will both be about
steady. Determine the saturation pressure of the refrigerant corresponding to
the condenser water temperature, leaving and entering water temperature will
of course be the same. If the actual pressure in the condenser is much above
this saturation pressure, it is clear that non-condensable gasses are present and
the system should be purged through the purge valve provided on top of the
condenser.

On self contained systems where the condenser is an integral part of the
refrigeration unit and is slung under the compressor baseplate, the discharge
service valve being the highest point over the condenser, presents a convenient
point to purge.

1. Back seat the service valve.

2. Discount the gauge from its outlet connection on this valve.

3. Slowly turn the valve system off the back seat from one to two turns.
Air will blow off if this is done slowly.

On central remote installations, a separate purge valve is generally
provided which is located at a highest point on the discharge line. On
such system this valve should be used for purging non-condensable
gases.

ADDING OIL TO THE COMPRESSOR :

If the crank case oil level is low, add oil to the system to bring oil to the
correct level. Use capella ‘D’ or equivalent lubricant oil. Oil must be taken
out only from sealed airtight tins. Do not use oil from open drums or
containers.