Thermo King T-500R Maintenance Manual page 56

Purge Mode (UT-Series)
Purge Mode is similar to Condenser Evacuation Mode in previous systems. It is used to move the refrigerant out of the
condenser into the accumulator when the unit shifts from Cool (or Null) to Heat or Defrost. The unit goes into Purge Mode for
20 to 100 seconds before shifting to Heat or Defrost. The ambient and return air temperatures determine the duration. Lower
temperatures cause the unit to stay in Purge Mode longer.
High pressure refrigerant vapor leaves the compressor and flows through the open CIS and condenser to the receiver tank, The
PV is open so most of the refrigerant flows through the PV to the accumulator. Some of the refrigerant flows through the drier,
heat exchanger, expansion valve, and evaporator to the accumulator. From the accumulator the refrigerant returns to the
compressor.
Solenoid and Check Valves
1. Condenser Inlet Solenoid (CIS)-Open/ De-energized
2. Liquid Injection Solenoid (LIS)-Closed/ De-energized but the microprocessor will open it if necessary to control compressor
temperature.
3. Condenser Check Valve-Open
4. Purge Valve (PV)-Open/Energized
5. Hot Gas Solenoid (HGS)-Closed/ De-energized
5
4
3
Purge Mode T-500R/T-Dairy
Unit Description
6
2
1
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