Thermo King – Low Side Pump Down

WARNING: New pump-down service techniques are required when working on scroll compressors.
• When pumping down scroll compressors always operate the unit in low speed.
• Only pump the unit to a 5-10 inch vacuum. Running the unit into a deep vacuum will damage the compressor.
• Never run the unit with the low side in a vacuum for more than 1 minute.

If a unit has lost cooling capacity and has high suction pressure, an internal high to low side leak may be the problem. A low side pump down will check the following internal seal points:
• Evaporator side of 3-way Valve
• Pilot Solenoid
• Compressor Discharge Check Valve
• Low Side External Leak
• Thermax Solenoid
• Liquid Injection Valve

Purpose: A low side pump down will allow you to change the drier and service other low side components.
Low Side Pump Down Procedure
1. Install a calibrated gauge manifold per “Installing and Purging a Gauge Manifold with Low Loss Fittings” on page 12.
2. Start the unit and enter Service Test Mode as shown by Service Procedure A34A in the MP-T Diagnostic Manual (TK 41087). Using Service Test Mode place the unit in low speed cool [tESt-LSC].
3. Front seat the receiver tank outlet valve.
4. Run until a suction pressure of 5-10 inches vacuum is reached. Do not run the unit in a vacuum for more than 1 minute.
5. Turn the unit off.
6. Suction pressure should raise somewhat but stop. If it continues to rise, this indicates an internal leak.

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