(4) Record the temperatures indicated by both thermometers and the pressures indicated by both pressure
(5) Compare the readings obtained from pressure testing with the normal ranges shown in Table 5-1.
d. Analysis of Discrepancies. If actual pressure-temperature relationships differ from those shown
consider the following reasons, and take appropriate action.
(2) If pressures are too low: Check for leaks (paragraph 5.24). repair, recharge the system and repeat the --
pressure test (paragraphs 5.26 and 5.27).
(2) If pressures are too high: Close the suction service valve, remove the pressure gauge, and bleed off the
appropriate amount of refrigerant. Repeat the pressure test.
(3) If discharge pressure is extremely high and suction pressure is extremely low. blockage may exist in the
refigeration system. Troubleshoot, correct the trouble. recharge if necessary. and repeat the pressure teat.
e. Completion. After pressure testing has been successfully completed. close both service valves, remove "
gauges, install caps on service valves. and install fresh air screen, using five screws to secure it. Remove thermometers
from the unit.
5.28. Compressor Motor Burnout.
Burnout of a compressor motor is indicated by lack of continuity of the motor windings and the condition of compressor
oil. which must be determined after the compressor has been removed from the refrigeration system. Causes of
compressor motor burnout include the following:
a. Low line voltage, which causes motor windings to over heat. Before burning out completely, the overheated
windings cause chemical breakdown of the refrigerant and the oil to form sludge and other system contaminants.
b. Loss of refrigerant. An inadequate charge of refrigerant gas in system reduces the amount of cooling gas
within the compressor. resulting in gradual overheating of the motor and failure of the winding.
c. High head pressure. High head
or dirty condenser coils
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 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
hydrofluoric 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.
5.29. 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
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 contaminants from causing repeated burnouts when the compressor is replaced.
5.30. Cleaning Out The Refrigeration System After Burnout
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, act as follows: