Thermo King – Compressor Pump Down for Diagnosis

Purpose: To check for internal leaks through the discharge valve plates and the pilot solenoid and to perform service work on the compressor.

Compressor Pump Down Procedure
1. Install a calibrated gauge manifold.
2. Operate the unit in high speed cool 5 minutes or more.
3. Front seat the suction service valve and pump down the compressor to 20 to 25 inches of vacuum.
4. Stop the unit. Crankcase pressure should remain below zero psig for 15 seconds or more. If pressure rises above 0 psig, repeat pump down up to 3 times.

If pressure still rises:
• to zero and stops – indicates low pressure area leak to the atmosphere.
• above zero – indicates internal high pressure to low pressure area leaks through valve plates or pilot solenoid.

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