Refrigeration Maintenance 10-18
Remove Evacuation Hoses
Refer to Thermo King Truck and Trailer Diagnosing Manual for correct procedure
HIGH PRESSURE CUTOUT
The high pressure cutout (HPCO) is located on the compressor discharge manifold. If the discharge pressure exceeds the pressure
switch setting, the switch opens the 8D circuit, de-energizing the fuel solenoid to stop the unit. See Specifications chapter
for
switch settings.
It is identified by it’s yellow coloured wires
HEAD PRESSURE CONTROL SWITCH (SL TCI and SL Spectrum)
The Head Pressure Control Switch (HPCS) is located on the compressor discharge manifold. The HPCS controls the operation
of the Purge Valve (PV) and RTPS as a back up should the discharge transducer fail. See Specification Chapter for switch
settings.
THREE-WAY VALVE CONDENSER PRESSURE BYPASS CHECK VALVE
(Single Temperature units only)
The condenser pressure bypass check valve is built into the three-way valve. This check valve controls the bypass flow of
refrigerant gas between the condenser inlet line and compressor discharge line.
The check valve is closed when the unit is operating on cool, or whenever the discharge pressure is higher than the condenser
pressure.
When the unit is operating on defrost or heat, or if the condenser pressure is higher than the discharge pressure, the check valve
opens and the condenser pressure is bled off until it decreases to the level of the discharge pressure. This improves
heating/defrosting performance and three-way valve response.
To check the operation of the valve:
1. Remove the condenser pressure bypass check valve cap from the three-way valve.
2. Using a screwdriver, gently turn the check valve stem clockwise until the valve is front seated.
Three-way Valve Condenser Pressure Bypass Check
Valve
1. Three-way Valve Cool Position
2. Check Valve Closed
3. Three-way Valve Heat/Defrost Position
4. Check Valve Open
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