TM 9-4120-357-14
b. Loss of refrigerant. An inadequate charge of refrigerant gas in the system reduces the amount of cooling gas
within the compressor, resulting in gradual overheating of the motor and failure of the winding.
c. High headpressure. High head pressures can be caused by clogged or dirty condenser coils or screens, or by
an inoperative condenser fan. High head pressure requires the compressor to work harder, creating additional heat
which ultimately can result in motor burnout. Poor ventilation around the condenser, operating with the deflector door
closed, and extremely high ambient temperatures can also cause motor failures.
d. Moisture in system. Leakage of air into the refrigeration system starts a chain reaction which can result in
motor burnout. Air contains oxygen and moisture which combine with refrigerant gas to form hydrochloric and hydroflu-
oric acids. These combine with compressor oil to form an acid sludge which is carried throughout the system, and which
attacks the motor windings, causing short circuits and burnout.
5-10. Diagnosing Compressor Motor Burnout.
It is important to diagnose the type of compressor motor failure for two reasons. Simple failure, without motor burnout,
does not require the extensive cleaning of the entire refrigeration system that burnout requires. Also, motor burnout indi-
cates other problems that have contributed to the failure, and these problems must be corrected or avoided to prevent
repetition of the burnout. After removal of a bad compressor from the refrigeration system, remove all external tubing
and tip the compressor toward the discharge port to drain a small quantity of oil into a clear glass container. If the oil is
clean and clear, and does not have an acrid smell, the compressor did not fail because of motor burnout. If the oil is
black, contains sludge and has an acrid odor the compressor failed because of motor burnout, and the refrigeration sys-
tem must be cleaned to prevent residual contaminants from causing repeated burnouts when the compressor is replaced.
5-11.
Cleaning Out the Refrigeration System After Burnout.
WARNING
Avoid inhaling fumes and burns from any acid formed by burn out of oil and refrigerant.
Wear gas mask if area is not thoroughly ventilated. Wear protective goggles or glasses
to protect eyes. Wear rubber gloves to protect hands. Use care to avoid spilling com-
pressor burn out sludge. If sludge is spilled, clean area thoroughly.
You must clean the entire refrigeration system after a burnout has occurred. Since contaminants will have-been carried
to many corners and restrictions in the piping and fittings. These contaminants will soon mix with new refrigerant gas and
compressor oil to cause repeated burnouts. To clean the system thoroughly, proceed as follows:
a. Remove the drier-strainer, and blow down each leg of the refrigeration system. To do this connect a cylinder or
dry nitrogen to each drier-strainer connection, in turn, and open the cylinder shutoff valve for at least 30 seconds at 50
PSIG (3.5 KG/CM2) pressure.
b. Connect the two drier-strainer fittings with a jumper locally manufactured from refrigerant tubing and fittings,
and install a pump reservoir and filter in place of the compressor. (See Figure 5-1).
c. Disassemble both expansion valves (V4 and V5, Figure 5-1) and temporarily remove the valve cages. Re-
install shell of power assembly using a locally manufactured gasket between power assembly and body to prevent leak-
age. Tag and retain valve cages for use at re-assembly.
NOTE
An unused drier-strainer or other suitable medium may be used as the filter.
d. Fill reservoir with fluorocarbon refrigerant, R11, and start the pump. Continue filling the reservoir with refriger-
ant, R11, until it begins to pour out of the return line. Continue flushing for at least 15 minutes.
NOTE
During flushing and back-flushing operations, apply 24 volts, DC, to the bypass
line solenoid valve (K4) for a total of approximately 10 minutes to each cycle. This
will ensure that the cleaning solvent is forced through all parts of the system.
5-10