- M U F F L E R S | MUFFLERS - |
COMPRESSORSCOMPRESSORS
Fig. 9 - Thermistor Locations
Step 4 - Check Thermistors That Control EXV - Check thermistors that control processor output voltage pulses to EXVs. Circuit A thermistors are T5 and T7. Circuit B thermistors are T6 and T8. Refer to Fig. 9 for location.
1.lJse the temperature subfunction of the status function (pp=]) to determine if thermistors are reading
correctly.
2.Check thermistor calibration at known temperature by measuring actual resistance and comparing value measured with values listed in Table 8.
3.Make sure that thermistor leads are connected to proper pin terminals at 157 terminal strip on processor module and that thermistor probes are located in proper position in refrigerant circuit (Fig. 9).
When above checks have been completed, actual operation of EXV can be checked by using procedures outlined in Step 5.
Step 5 ~ Check Operation of the EXV ~ Use following procedure to check actual operation ofelectronic expan- sion valves.
I. Close liquid line service valve for circut to be checked
and run through the Quick Test step (in subfunction 3 of test function) for the lead compressor in that circuit to pump down the low side of the system.
Repeat test step 3 times to ensure that all refrigerant has been pumped from low side.
NOTE: Be sure to allow compressors to run full 10 seconds at each step.
2.Turn OFF compressor circuit breaker(s). Close com- pressor service valves and vent any remaining refrig- erant from low side of system.
3.Remove screws holding top cover of EXV. Carefully remove top cover, using caution to avoid damage to
the motor leads. If EXV plug was disconnected during | ,:’ | |
this process, reconnect it after the cover is removed. | ‘: | |
4. Enter appropriate EXV Quick Test step for EVXA or |
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EXVB in the outputs subfunction of the test function |
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Press ENTR to initiate test. With cover |
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lifted off the EXV valve body, observe operation of valve motor and lead screw. The motor should turn in the clockwise direction and the lead screw should move down into the motor hub until the valve is fully closed or fully open depending on whether you initiate the open or close test step for that valve. Lead screw movement should be smooth and uniform from fully open to fully closed position, or from fully closed to fully open.
If valve is properly connected to processor and receiv- ing correct signals, yet does not operate as described above, the valve shouId be replaced.
The operation of the EXV valve can also be checked without removing the top cover. This method depends on the operator’s skill in determining whether or not the valve is moving, To use this method, initiate the Quick Test to open the valve. Immediately grasp the EXV valve body with the hand. As the valve drives open, a soft, smooth pulse will be felt for approximately 26 seconds as the valve travels from fully closed to fully open. When the valve reaches the end of its opening stroke, a hard pulse will be felt momentarily. Drive the valve closed and a soft, smooth pulse will be felt for the 26 seconds necessary for the valve to travel from fully open to fully closed. When the valve reaches the end of its stroke, a hard pulse will again be feelt as the valve overdrives by 50 steps. The valve should be driven through at least 2 complete cycles to be sure it is operating properly. If a hard pulse is felt for the 26 second duration, the valve is not moving and should be replaced.
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