Carrier 040-420 Installation And Service Manual

_ I . :,/:.::.i .‘IBecause the EXVs are controlled by the processor mod-ule, it is possible to track valve position. During initialstart-up, EXV is fully closed. After start-up, valve po-sition is tracked by processor by constantly observingamount of valve movement.The processor keeps track of EXV position by countingthe number of open and closed steps it has sent to eachvalve. It has no direct physical feedback of valve posi-tion. Whenever unit is switched from STOP to RUN po-sition, both valves are initialized, allowing the proces-sor to send enough closing pulses to the valve to move itfrom fully open to fully closed, then reset the positioncounter to zero.4. The EXV test can be used to drive EXV to any desiredposition. When EXV opens, the metering slots begin toprovide enough refrigerant for operation at these steps:step 60 for sizes 040-210 and associated modular units,or 145 for sizes 225, 250, and 280. This is fully closedposition when circuit is operating. The fully open posi-tion is 760 steps.5. Check thermistors and pressure transducers that controlEXV. Check thermistors and pressure transducers thatcontrol processor output voltage pulses to EXVs. SeeFig, 13 for locations.Circuit A - Thermistor T7, Suction Pressure Trans-ducer SPTACircuit B - Thermistor T8, Suction Pressure Trans-ducer SPTBa. Use temperature subfunction of the status function(m bi ) to determine if thermistors are readingcorrectly.b. Check thermistor calibration at known temperatureby measuring actual resistance and comparing valuemeasured with values listed in Tables 15 and 16.c. Make sure thermistor leads are connected to properpin terminals at 57 terminal strip on processor mod-ule and that thermistor probes are located in properposition in refrigerant circuit. See Fig. 14 and 15.d. Use the pressure subfunction of the Status function( m Fl) to determine if pressure transducers arereading correctly. Connect a calibrated gage to leadcompressor suction or discharge pressure connectionto check transducer reading.e. Make sure transducer leads are properly connected injunction box and at processor board. Check trans-former 5 output. Check voltage transducer 5 vdc +.2 v.When above checks have been completed, check ac-tual operation of EXV by using procedures outlinedin Step 5.6. Check operation of EXV.a. Close liauid line service valve of circuit to be checked,and run ihrough the test step ( 17 Fi ) for lead com-nressor in that circuit to pump down low side of sys-iem. Repeat test step 3 tcmes-to ensure all refrigeranthas been pumped from low side.NOTE: Be sure to allow compressors to run for thefull 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. Carefullyremove 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 orEXVB in the outputs subfunction of the test function(jlF[). Press-mmriH to initiate test. Withcover lifted off EXV valve body, observe operationof valve motor and lead screw. The motor shouldturn counterclockwise, and the lead screw should moveup out of motor hub until valve is fully open. Leadscrew movement should be smooth and uniform fromfully closed to fully open position. Press l-+$0check open to closed operation.If valve is properly connected to processor and re-ceiving correct signals, yet does not operate as de-scribed above, valve should be replaced.Operation of EXV valve can also be checked withoutremoving top cover. This method depends on oper-ator’s skill in determining whether or not valve ismoving. To use this method, initiate EXV test andopen valve. Immediately grasp EXV valve body. Asvalve drives open, a soft, smooth pulse is felt for ap-proximately 26 seconds as valve travels from fullyclosed to fully open. When valve reaches end of itsopening stroke, a hard pulse is felt momentarily. Drivevalve closed and a soft, smooth pulse is felt for the26 seconds necessary for valve to travel from fullyopen to fully closed. When valve reaches end of itsstroke, a hard pulse is again felt as valve overdrivesby 50 steps. Valve should be driven through at least2 complete cycles to be sure it is operating properly.If a hard pulse is felt for the 26 second duration, valveis not moving and should be replaced.The EXV test can be repeated as required by enter-ing any percentage from 0 ( r;l ) to 100 to initiatemovement.If operating problems persist after reassembly, theymay be due to out-of-calibration thermistor(s) or inter-mittent connections between processor board terminalsand EXV plug. Recheck all wiring connections and volt-a g esignals,Other possible causes of improper refrigerant flow con-trol could be restrictions in liquid line, Check for pluggedfilter drier(s) or restricted metering slots in the EXV.Formation 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 expectedwhen leaving fluid temperature from the cooler is below40 F. Clean or replace valve if necessary.NOTE: Frosting of valve is normal during compressorTest steps and at initial start-up. Frost should dissipateafter 5 to 10 minutes operation in a system that is oper-ating properly. If valve is to be replaced, wrap valvewith a wet cloth to prevent excessive heat from damag-ing internal components.57