Carrier 30GN040-420 operating instructions Thermistor Replacement T1, T2, T7, T8

reading correctly. Connect a calibrated gage to lead compressor suction or discharge pressure connection to check transducer reading.

e.Make sure transducer leads are properly connected in junction box and at processor board. Check trans-

former 5 output. Check voltage transducer 5 vdc 6 .2 v.

When above checks have been completed, check ac- tual operation of EXV by using procedures outlined in this step.

6.Check operation of EXV.

a.Close liquid line service valve of circuit to be checked,

and run through the test step ( ) for lead com- pressor in that circuit to pump down low side of sys- tem. Repeat test step 3 times to ensure all refrigerant has been pumped from low side.

NOTE: Be sure to allow compressors to run for the full pumpout period.

b.Turn off compressor circuit breaker(s). Close com- pressor discharge service valves and remove any re- maining refrigerant from low side of system.

c.Remove screws holding top cover of EXV. Carefully remove top cover. If EXV plug was disconnected dur- ing this process, reconnect it after cover is removed.

When removing top cover, be careful to avoid dam- aging motor leads.

d.Enter appropriate EXV test step for EXVA or EXVB in the outputs subfunction of the test function

( ). Press to initiate test. With cover lifted off EXV valve body, observe operation of valve motor and lead screw. The motor should turn counterclockwise, and the lead screw should move up out of motor hub until valve is fully open. Lead screw movement should be smooth and uniform from

fully closed to fully open position. Press	to
check open to closed operation.

If valve is properly connected to processor and receiv- ing correct signals, yet does not operate as described above, valve should be replaced.

Operation of EXV valve can also be checked without removing top cover. This method depends on opera- tor's skill in determining whether or not valve is mov- ing. To use this method, initiate EXV test and open valve. Immediately grasp EXV valve body. As valve drives open, a soft, smooth pulse is felt for approxi- mately 26 seconds as valve travels from fully closed to fully open. When valve reaches end of its opening stroke, a hard pulse is felt momentarily. Drive valve closed and a soft, smooth pulse is felt for the 52 sec- onds necessary for valve to travel from fully open to fully closed. When valve reaches end of its stroke, a hard pulse is again felt as valve overdrives by 50 steps. 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, valve is not moving and should be replaced.

The EXV test can be repeated as required by enter-

ing any percentage from 0 ( ) to 100 to initiate movement.

If operating problems persist after reassembly, they may be due to out-of-calibration thermistor(s) or intermittent connections between processor board terminals and EXV plug. Recheck all wiring connections and voltage signals.

Other possible causes of improper refrigerant ¯ow con- trol could be restrictions in liquid line. Check for plugged ®lter drier(s) or restricted metering slots in the EXV. For- mation of ice or frost on lower body of electronic ex- pansion valve is one symptom of restricted metering slots. However, frost or ice formation is normally expected when leaving ¯uid temperature from the cooler is below 40 F. Clean or replace valve if necessary.

NOTE: Frosting of valve is normal during compressor test steps and at initial start-up. Frost should dissipate af- ter 5 to 10 minutes operation in a system that is operating properly. If valve is to be replaced, wrap valve with a wet cloth to prevent excessive heat from damaging internal components.

Thermostatic Expansion Valve (TXV) Ð Refer to base unit Installation Instructions for TXV information (30GN040,045 with optional brine only).

Thermistors Ð All thermistors are identical in their tem- perature vs. resistance performance. Resistance at various tem- peratures are listed in Tables 17 and 18.

LOCATION Ð General location of thermistor sensors are shown in Fig. 14.

Cooler Leaving Fluid Thermistor (T1) Ð T1 is located in leaving ¯uid nozzle. The probe is immersed directly in the ¯uid. All thermistor connections are made through a 1¤4-in. coupling. See Fig. 16. Actual location is shown in Fig. 14 and 15.

Cooler Entering Fluid Thermistor (T2) Ð T2 is located in cooler shell in ®rst baffle space near tube bundle. Thermistor connection is made through a 1¤4-in. coupling. See Fig. 16. Actual location is shown in Fig. 14 and 15.

Compressor Suction Gas Temperature Thermistors (T7 and T8) Ð T7 and T8 are located in lead compressor in each circuit in suction passage between motor and cylinders, above oil pump. They are well-type thermistors. See Fig. 14 and 15.

THERMISTOR REPLACEMENT (T1, T2, T7, T8)

Thermistors are installed directly in ¯uid Relieve all pres- sure using standard practices or drain ¯uid before re- moving.

Proceed as follows (see Fig. 16): To replace thermistor sensor T2:

1. Remove and discard original thermistor and coupling.

IMPORTANT: Do not disassemble new coupling. Install as received.

2.Apply pipe sealant to 1¤4-in. NPT threads on replacement coupling and install in place of original. Do not use pack- ing nut to tighten coupling. This damages ferrules (see Fig. 16).

3.Insert new thermistor in coupling body to its full depth. If thermistor bottoms out before full depth is reached, pull thermistor back out 1¤8 in. before tightening packing nut. Hand tighten packing nut to position ferrules, then ®nish tightening 11¤4 turns with a suitable tool. Ferrules are now attached to thermistor which can be withdrawn from cou- pling for unit servicing.

To replace thermistors T1, T7, and T8:

Add a small amount of thermal conductive grease to ther- mistor well. Thermistors are friction-®t thermistors, which must be slipped into well located in the compressor pump end.

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