Zamil PDS Series Installation, Operation & Maintenance Manual - Refrigeration
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REFRIGERATION
COMPRESSOR
Single scroll compressor for models PDS036 to PDS075 and dual scroll compressors for model PDS090 to PDS600 are
used as standard. Optional single semi-hermetic compressor for models PDS036 to PDS150 (single circuit). All other
models are dual semi-hermetic compressors (dual circuit). The compressors are equipped with internal motor protection
and also provided with vibration isolators. Oil pressure control is provided on units with semi-hermetic compressor only.
Each compressor has lockout devices to protect it from short cycling when tripped by safety controls. The compressor
motors conform to NEMA MG-1 & MG-2.
Scroll Compressors
are used in some of these units. The major benefits being:
1. Low Sound Level: Quieter operation because of no dynamic suction and discharge valves action.
2. Low vibration and discharge pulses.
3. High Energy Efficiency: Because of high volumetric efficiency it minimize pressure and heat transfer losses.
4. High Capacity: Due to its high mass flow and high compression ratios.
5. High Durability: With its robust design, few moving parts, low motor strains, large internal volume for liquid handling
makes this compressor highly reliable.
6. High Charge Limit: Therefore, lower applied costs as no suction accumulator required, no need for pump down
system and check valve in discharge line.
Low capacity can be caused by inefficient compressor, that is, the compressor does not pump sufficient quantity of
refrigerant, even though a full charge is available in the system.
Electrical and mechanical tests should be performed to determine if the compressor is defective. If the compressor is found
to be all right but the electrical components are defective, remove and replace the defective electrical components only.
Below are some tests that should be performed on the compressor to determine, if the compressor is defective.
1. Test compressor motor winding for ground.
2. Test compressor motor windings for continuity.
3. Test that compressor motor will run both without a load and under a load.
4. Test the current or ampere drawn.
5. Observe sound level of compressor.
To establish that the compressor suction and discharge valves are operating and holding properly, attach gauges to the
liquid and suction service valves. "Front seat" the liquid service valve.
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.