Thermo King UT-1200, Manual

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Unit Description
35
Purge Mode
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 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.
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. Receiver Tank Pressure Check Valve-Closed
5. Purge Valve (PV)-Open/Energized
6. Purge Check Valve-Open
7. Hot Gas Solenoid (HGS)-Closed/
De-energized
Figure 8: Purge Mode
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