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TM5-4120-376-14
5-22. COMPRESSOR, ACCUMULATOR AND RELATED PARTS/Replace (Cont)
L O C A T I O N / I T E M
Test:
3. High head pressure. 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, and extremely high ambient temperature can also cause motor
failures.
4. 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 hydrofluoric acids. These combine with compressor oil
to form an acid sludge which is carried throughout the system, and which attacks the motor
winding, causing short circuits and burnout.
Diagnosing Motor Burnout. It is important to diagnose the type of compressor failure for two
reasons. Simple failure, without motor burnout, does not require the extensive cleaning of the
entire refrigeration system that a major failure requires. Also, motor burnout indicates 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 system must be cleaned to prevent residual contaminates from causing repeated
burnouts when the compressor is replaced.
Cleaning Out the Refrigeration System After Burnout.
WARNING
Purge system with dry nitrogen prior to soldering. Refrigerant heated to
1200° F (649°C) creates phosegene gas.
WARNING
You must clean the entire refrigeration system after a burnout has occurred,
since contaminates will have been carried to many corners and restrictions in
the piping and fittings. These contaminates will soon be mixed with new
refrigerant gas and compressor oil to cause repeated burnouts. To clean the
system throughly, act as follows:
NOTE
An unused filter-drier or other suitable medium may be used as the filter.
5-65
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