3. HIGH HEAD PRESSURE
High head pressure is a third cause of motor burn out.
With high head pressure the motor load is increased
and the increased current causes the windings to over-
heat and eventually fail. Poor circulation of air over the
high side condenser can cause motor failure for this
reason. Another cause of excessive head pressure may
be caused by air in the system.
4. MOISTURE
The fourth major cause of motor burn out is moisture. It
takes very little moisture to cause trouble. In the com-
pressor dome refrigerant is mixed with lubricating oil
and heat from the motor windings and compressor oper-
ation. If there is any air present, the oxygen can combine
chemically with hydrogen in the refrigerant oil to form
water. Just one drop of water no matter how it gets into
the system can cause trouble.
When the water comes in contact with the refrigerant oil,
in the presence of heat, hydrochloric or hydrofluoric acid
is formed. These acids destroy the insulation on the
motor windings. When the winding short circuits, a
momentary temperature of over 3000° F. is created.
Acids combine chemically with the insulation and oil in
the compressor dome to create sludge, which quickly
contaminates the refrigeration system.
Sludge collects in various places throughout the system
and is very hard to dislodge. A purge of the refrigerant
vapor through the system will not clean the system.
If any of these cases have occurred, an acid test kit
should be used to determine the true condition of the oil.
REFRIGERANT FLOW STOPPED
This condition may result in continuous running of the
compressor or it may cycle on overload depending on
the refrigerant charge and load conditions. High tank
temperatures result. This condition may be caused by a
restricted capillary tube due to moisture freezing at the
outlet end of the tube or foreign matter plugging the line.
The major part of the refrigerant charge will be pumped
into the high side resulting in very low suction pressure.
Moisture on a properly serviced system is a remote
possibility. However, if moisture does enter the system
with air drawn in on the suction side of the system or
during service operation, it will eventually freeze and
restrict or completely stop the flow of refrigerant into the
low side.
If this condition should occur, pull the service cord and
allow the cabinet to warm up to a temperature above
32°F. or room temperature. This warm up can be accel-
erated by the use of heat lamps inside the cabinet. 100
watt lamps can also be used to accelerate the warm up
period.
After the cabinet has warmed up sufficiently to melt the
ice and relieve the restriction in the capillary line, reclaim
refrigerant charge down to zero pounds gauge pres-
sure. Blow out the low side and high side with nitrogen.
Follow the instructions given under “COMPLETE
RECHARGE OR REFRIGERANT” including replace-
ment of the filter drier.
If the capillary line is plugged with foreign matter or dirt,
exert a pressure backwards through the line to free it.
Proceed as follows:
1. Install a compound gauge on the suction line to deter-
mine whether or not the low side is under a vacuum
or a pressure. If the low side is under a vacuum, hook
manifold gauge to a cylinder of dry nitrogen and
pressurize system to 0 pounds.
2. Disconnect the capillary line from the low side inlet
and remove the filter drier. Exert a vapor pressure in
the reverse direction through the capillary by “crack-
ing” the drum valve. Allow the pressure to build up to
about 75 pounds if necessary to clear out any foreign
matter.
CLEANING SYSTEM AFTER BURN OUT
1. Install the service taps and reclaim all refrigerant in
cabinet.
2. Remove the inoperative compressor and filter drier.
3. Obtain a sample of oil and check the condition with an
acid test kit.
4. Connect the oil cooler lines together.
5. Most reclaimers have the ability to push liquid refrig-
erant through the system and back to the reclaimer
for cleaning.
Once this has been accomplished:
6. Install new compressor and filter drier.
7. Evacuate system below 500 microns.
8. Check serial rating plate for charge and weigh in cor-
rect amount.
GENERAL OPERATIONS
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