Start the compressor, allowing it to operate long enough to pump down to approximately 1 PSIG. Shut the compressor off
and observe the compound gauge. The gauge pressure may build rapidly. Repeat the pump down process several times
observing the gauge pressure each time after the compressor stops. If the gauge pressure builds rapidly each time after
the compressor stops, it indicates that the compressor discharge valves are not holding and refrigerant is leaking from
the high side to the low side of the compressor.
To check the suction valves, assuming that the discharge valves are holding, allow the compressor to operate long
enough to pump down the system to approximately 10 inches of vacuum. If the compressor required longer time to
accomplish this, then the suction valves are not holding and the compressor should be changed out as it is defective.
MOTOR COMPRESSOR BURN OUT PROCEDURE
The extent of the contamination in a system will indicate the amount of clean-up necessary. If a compressor had burned
out, the following method of clean-up is recommended:
1. Discharge the refrigerant from the system.
2. Replace the inoperative compressor.
3. Clean up the system thoroughly and remove all the contaminations.
4. Install a system cleaner or filter drier in the suction line and replace the liquid line filter drier.
5. Connect a vacuum pump to both the low and the high side of the system to remove air and other non-condensables
from the system.
6. Allow the vacuum pump to operate until a pressure of 500 microns is achieved.
7. Recharge the system and allow it to operate 8 to 12 hours.
8. Take an oil sample and test for acidity.
If the first acidity test shows that the acid content is below the safe level, as indicated in the test kit instructions, and the
oil is clean, the clean-out system can be removed. If an in-line suction filter drier was used, it can remain in the system
provided the pressure drop through the filter does not exceed the manufacturers listed pressure drop. For a badly
contaminated system that indicates acid in the oil after 8 to 12 hours of operation, change the suction and liquid line filter-
driers and check the system after 24 hours of operation.
There are instances where contaminants are discovered in a refrigeration system with the compressor still operational.
The same procedure applies, when cleaning these systems, as on a compressor burn-out.
SOURCE OF CONTAMINATION
There are many ways in which a refrigerant system can become contaminated. The most common of these are as
follows:
1. Improper or inadequate dehydration.
2. Wet refrigerant.
3. Wet oil (caution: It is best to purchase oil in small containers and use as needed. Open containers will absorb mois-
ture).
4. Refrigerant leaks (allowing system to operate in a vacuum).
5. Failure to remove oil and moisture after having opened the system for repair.
6. Higher than normal operating temperatures and pressures will cause a breakdown of the oil and refrigerant.
7. Improper use of soldering or brazing flux.
HIGH PRESSURE SWITCH
A high pressure switch is located in the discharge line and senses the discharge pressure. Should the discharge pressure
exceed 350 psig, the control will open turning off the compressor. The control is designed to protect against excessive
discharge temperatures and pressures which can cause compressor overheating and damage to the motor windings or
valves.
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