Thermo King – Compressor Capacity Test

Purpose: To test compressor piston reed condition, piston to cylinder clearance, piston and cylinder condition, and compressor performance capability.
Preparations Before the Test
1. Ambient temperature must be above 60 F (15 C).
2. Install a calibrated gauge manifold.
3. Check the refrigerant charge (correct amount if needed).
4. Check/adjust compressor RPM.
5. Check for low side restrictions – pressures must be normal or
high on the suction side.
6. Perform low side pumpdown and throttling valve check.
Repair before continuing.
7. Warm the evaporator (operate in heat/defrost if needed).

Compressor Capacity Test Procedure
1. Operate the unit in cool and cover the condenser coil to build
discharge pressure.
• R-12, R-401B and R-134a = 250 psig
• R-502, R-22, R-402A, R-403B and R-404A = 300 to 350 psig
2. Pump down the low side, while keeping the condenser coil covered.
3. When low side pumps down to a 10 inch vacuum, read discharge pressure. It should read as indicated or higher.
R-12, R-401B and R-134a = 125 psig or more.
R-502, R-22, R-402A, R-403B and R-404A = 200 to 250 psig or more.

NOTE: Compressors not meeting these specifications may function satisfactorily for higher box temperature applications but most compressors need repair.

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