Thermo King T-500R Maintenance Manual page 55

Purge Mode (T-500R/T-Dairy)
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. The unit goes into Purge Mode for 20 to 100
seconds before shifting to Heat. 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 to the condenser. The PV is open so
most of the refrigerant flows from the condenser through the PV and the purge check valve to the accumulator. Some of the
refrigerant flows through the condenser check valve, receiver tank, drier, heat exchanger, expansion valve, and evaporator to the
accumulator. From the accumulator the refrigerant returns to the compressor through the SPR.
Solenoid and Check Valves
1. Condenser Inlet Solenoid (CIS)-Open/ De-energized
2. Condenser Check Valve-Open
3. Receiver Tank Pressure Check Valve-Closed
4. Purge Valve (PV)-Open/Energized
5. Purge Check Valve-Open
6. Hot Gas Solenoid (HGS)-Closed/ De-energized
3
Heat/Defrost Mode UT-Series
Unit Description
4
1
5
2
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