Refrigeration Maintenance and Service Operations
137
3. Check the heater circuit and thermistor circuit
resistance.
•
A good heater circuit has a resistance of 20
ohms at 25 C (78 F).
•
A good thermistor circuit has a resistance of
20,000 ohms at 25 C (78 F).
NOTE: The ohmmeter will display a slightly
higher heater resistance if the valve was
energized just prior to testing the circuit
resistance.
4. To return the unit to service, plug the
evaporator pressure regulator valve lead
connector into the unit wire harness.
Valve Actuator Replacement
If the evaporator pressure regulator valve fails to
operate properly, remove the actuator cover and
inspect the assembly for rust or corrosion. Rust or
corrosion can damage the actuator or heater
circuit, preventing the valve from operating
properly.
1. To replace actuator assembly, unplug the
heater and thermistor lead wire harnesses.
2. Connect the unit’s main power cable to the
main power source and switch the
refrigeration unit’s On/Off switch to ON.
Close the liquid line service valve and pump
down the low side. Equalize suction pressure
to 21 kPa, 0.21 bar, 3 psig.
3. Turn the unit On/Off switch to OFF. Then
disconnect the main power cable from the
main power source again. Close (front seat)
the discharge service valve.
4. Inspect the actuator terminals and note the
wire connection sequence. Then disconnect
wire leads.
5. Unscrew the actuator assembly from the valve
body.
6. Immediately insert new actuator assembly in
valve body.
7. Thread new actuator into valve body until it is
hand tight. Then tighten to 45 N.m (33 ft-lb).
8. Connect wire leads to actuator terminals in
proper sequence.
9. Replace cover on actuator assembly.
10. Connect the heater and thermistor lead wire
harnesses.
11. Evacuate the low side.
12. Open the discharge valve. Then open the
liquid line service valve.
13. Verify that all personnel are clear and connect
main power plug to power supply. Place the
unit back in service.
CAUTION: Any time the discharge valve
is front seated, disconnect the unit power
source to prevent accidental compressor
start-up
Summary of Contents for CRR-40 119
Page 4: ......
Page 16: ...Safety Precautions 16...
Page 18: ...Service Guide 18...
Page 20: ...Model Features 20...
Page 32: ...Specifications 32...
Page 120: ...MP 3000a Controller 120...
Page 160: ...Wiring and Schematic Diagrams Index 160...
Page 161: ...161 MPC2000 Wiring Schematic...
Page 162: ...162 MPC2000 High Voltage Wiring Diagram...
Page 163: ...163 MPC2000 Low Voltage Wiring Diagram...
Page 164: ...164 MPC2000 WCC Wiring Schematic...