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absolute-zero
03-02-2008, 07:42 PM
Here is another great training document that I came across for servicing or diagnosing Thermo king open drive scroll compressors,,:)

Remember, open drive scroll compressors used on truck units differ from reciprocating compressors as follows:
1.Scroll compressors are not equipped with discharge valve plates.
2.The flow of refrigerant is essential to cool and lubricate the internal components of the compressor.

Low Side Pumpdown
Warning, new pump-down service techniques are required when working on scroll compressors.
1. When pumping down scroll compressors always operate the unit in low speed.
2. Only pump the unit to a 5-10 inch vacuum. Running the unit into a deep vacuum will damage the compressor.
3. Never run the unit with the low side in a vacuum for more than 1 minute.

Diagnosis
If a unit has lost cooling capacity and has high suction pressure, an internal leak may be the problem. A low side pumpdown will check the following internal seal points:
1. 3-way Valve Evaporator Seat
2. Pilot Solenoid
3. Compressor Discharge Check Valve
4. Low Side External Leak
5. Liquid injection valve

Service
A low side pumpdown will allow you to change the drier and service other low side components.
Procedure
1. Install a gauge set, Low loss fittings must be used.
2. Start the unit and enter Service Test Mode
3. Using Service Test Mode place the unit in low speed cool [tESt-LSC]
4. Front seat the receiver tank outlet valve.
5. Run until a suction pressure of 5-10 inches vacuum is reached. 6. Do not run the unit in a vacuum for more than 1 minute.
7. Turn the unit off.
Suction pressure should raise somewhat but stop. If it continues to rise, this indicates an internal leak.

High Side Pumpdown
Diagnosis
This procedure combines the functions of the 3-way Valve Heat Check and the Low Side Pumpdown. A high side pumpdown will check the 3-way valve condenser side seat.
It will check these internal seal points:

3-way Valve Evaporator Seat
Pilot Solenoid
Compressor Discharge Check Valve
Liquid injection valve

3-way Valve Condenser seat

A high side pump-down will allow service to the:

High pressure cutout switch
Relief valve
Drier and other low side componentsProcedure
1. Install a gauge set .Low Loss fittings must be used.
2. Front seat the condenser pressure by-pass check valve on the 3-way valve.
3. Start the unit and enter Service Test Mode. Using Service Test Mode place the unit in low speed cool [tESt-LSC]
4. Front seat the receiver tank outlet valve.
5. Run until a suction pressure of 5 to10 inches vacuum is reached. Do not run the unit in a vacuum for more than 1 minute.
6. Stop unit.
7. Without starting the unit, shift the 3-way valve using Service Test Defrost Mode (tESt-dEF).
The 3-way Valve should shift and gauge pressures should equalize near 0 psig and not rise.
Note: If the system was opened for service, it should be leak tested and evacuated before opening the receiver tank outlet valve.
WARNINGDo Not Operate Scroll Compressor with Service or Receiver Tank Valves Closed. Compressor Damage Will Occur.


Compressor Capacity Test
The scroll compressor can not be pumped down to check the efficiency of the compressor. Use the following procedure.

Diagnosis
Loss of cooling capacity at low box temperatures.

Procedure
1. Install a gauge set. Low Loss fittings must be used.
2.Run the unit in high speed cool for five minutes or more until pressures stabilize.
3.Note the discharge pressure on the high pressure gauge.
4.Cover the condenser to build discharge pressure.
Allow discharge pressure to raise at least 100 psig above the previously noted pressure

The compressor is probably faulty if it can not raise the discharge pressure at least 100 psig. Check all other possible causes of capacity loss before condemning a compressor.

Regards A-Z