Unit Description
33
Refrigeration System
Components
The refrigeration system controls are used to
control the operation of the refrigeration system as
required by the microprocessor. The
microprocessor determines these requirements by
considering the setpoint, the software, the setting
of programmable features and the information
supplied by the sensors. Refer to TK 51652, the
SPECTRUM
™
TS Microprocessor Diagnostic
Manual for additional information.
These three valves are located in the condenser
section of the unit. They are common to all zones.
• Condenser Inlet Solenoid - This valve
controls the flow of refrigerant to the
condenser. This solenoid is energized (closed)
when any compartment is operating in heat or
defrost mode. This is a normally open valve
.
• Receiver Tank Pressure Check Valve- This
check valve is used to equalize pressure in the
receiver tank in the off cycle.
• Purge Valve - The purge valve operates in the
heat or defrost mode to make sure adequate
refrigeration is available
.
The following components are located in the
condensing section of the unit and serve the scroll
compressor. They are controlled by compressor
temperature, suction pressure and discharge
pressure.
• Liquid Injection Valve (LIV) - This valve
helps control the temperature of the scroll
compressor. It is energized or pulsed (open)
when the scroll compressor temperature
exceeds a set value to inject liquid refrigerant
directly into the compressor. The liquid
refrigerant flashes to a gas to effectively cool
the compressor. This valve is normally closed.
This component is located between the liquid
line and the compressor in the condenser
section of the unit.
• Hot Gas Bypass Valve (HGB) - This valve
helps control suction pressure. If the suction
pressure falls below a set limit this valve is
energized (open) to allow hot refrigerant gas
to flow to the suction line until the suction
pressure rises to an acceptable level. This
valve is normally closed. This component is
located in the hot gas bypass line next to the
compressor. This valve uses a similar
technique for controlling compression ratios.
• Discharge Pressure Regulator (DPR) (This
component is a mechanical control device) -
This valve is used to increase the discharge
pressure during heat and defrost. The valve
controls discharge pressure mechanically
based on temperature and the actual system
pressure.
This valve is normally closed and opens when
the set pressure is reached. This component is
located in the hot gas line in the condenser
section of the unit
The following components are also located in the
main unit.
• High Pressure Cutout - The high pressure
cutout is located on the discharge line of scroll
compressors. This switch monitors the
discharge pressure at the compressor. The
switch is closed with normal pressures and
open with excessive pressures. The switch
will open and close at pressures determined by
the refrigerant used in the unit. It opens on
high discharge pressure to shut the unit down
to prevent damage.
• Discharge Pressure Transducer - This
transducer supplies the discharge pressure at
the compressor to the microprocessor. This
information is used by the microprocessor and
software to determine the unit operating
conditions.
• Suction Pressure Transducer - This
transducer supplies the suction pressure at the
compressor to the microprocessor. This
information is used by the microprocessor and
software to determine the unit operating
conditions. It should be noted that the suction
pressure transducer is located downstream of
the throttle valve. As a result, the suction
pressure displayed is compressor suction
pressure.
• Compressor Temperature Sensor - This
transducer supplies the compressor
temperature to the microprocessor. This
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