Carrier 38APS025 Manual

Also see for 38APD115: Installation instructions

Carrier 38APS025 Manual Manual pdf 144 page image

144Compressor Discharge Check Valve — A disk-type checkvalve in the discharge of the compressor prevents high pressuredischarge gas from flowing rapidly back through the compres-sor at shutdown. This same check valve prevents a high to lowside bypass in multiple compressor circuits.COMPRESSOR FUNCTIONAL CHECKA functional compressor test with the suction service valveclosed to check how low the compressor will pull suction pres-sure is not a good indication of how well a compressor is per-forming. Such a test may damage a scroll compressor. Thefollowing diagnostic procedure should be used to evaluatewhether a Copeland scroll compressor is working properly.1. Proper voltage to the unit should be verified.2. The normal checks of motor winding continuity and shortto ground should be made to determine if the inherentoverload motor protector has opened or if an internal mo-tor short or ground fault has developed. If the protectorhas opened, the compressor must be allowed to cool suffi-ciently to allow it to reset.3. Proper indoor and outdoor blower/fan operation shouldbe verified.4. With service gages connected to suction and dischargepressure fittings, turn on the compressor. If suction pres-sure falls below normal levels, the system is either low oncharge or there is a flow blockage in the system.5. If suction pressure does not drop and discharge pressuredoes not rise to normal levels, reverse any two of thecompressor power leads and reapply power to make surecompressor was not wired to run in reverse direction. Ifpressures still do not move to normal values, the com-pressor may be faulty. Reconnect the compressor leads asoriginally configured.6. To test if the compressor is pumping properly, the com-pressor current draw must be compared to publishedcompressor performance curves using the operating pres-sures and voltage of the system. If the measured averagecurrent deviates more than ±15% from published values,a faulty compressor may be indicated. A current imbal-ance exceeding 15% of the average on the three phasesshould be investigated further.COMPRESSOR REPLACEMENT — All models containscroll compressors and have from one to six compressors.38APD025-030 units utilize a single compressor per circuit.These compressors are mounted directly to the unit base. Allother sizes have multiple compressors per circuit. Multiplecompressor circuits are mounted in sets on mounting rails.1. Open and tag all disconnects following proper lock-outtag-out procedures. Use proper personal protective equip-ment.2. Remove the junction box cover and disconnect the com-pressor power and ground connections. See Fig. 167 or168.3. Disconnect and remove the crankcase heater from thecompressor. Save the ground screw for re-installationlater.4. If the compressor is equipped with a motor protectionmodule (Kriwan or CoreSense), disconnect the wiring tothe device.5. Remove the cable from the compressor junction box.6. If the compressor is a digital compressor, remove the dig-ital unloader solenoid (Fig. 169). Save the mountingscrew for re-installation later. Remove the harness fromthe junction box.7. Isolate the circuit and remove the refrigerant using stan-dard refrigeration techniques.8. If the circuit high pressure switch (HPS), discharge tem-perature thermistor (DTT), return gas thermistor (RGT),discharge pressure transducer (DPT), or suction pressuretransducer (SPT) are in an area where brazing could dam-age the sensor, remove the device from the line and se-cure it out of the way.9. For tandem and trio compressor circuits, remove the oilfrom the compressors as described in the section Remov-ing Oil on page 149. This is required to cut (tandem com-pressor circuits) or remove (trio compressor circuits) theoil equalizer line. For tandem compressor circuits, cut theoil equalizer with a tubing cutter in a convenient place tobe able to reconnect with a coupling.10. Remove the bolts securing the compressor. Be sure tosave all of the mounting hardware for compressor instal-lation.WARNINGDo not supply power to unit with compressor coverremoved. Failure to follow this warning can cause a fire,resulting in personal injury or death.WARNINGExercise extreme caution when reading compressor cur-rents when high-voltage power is on. Correct any of theproblems described below before installing and running areplacement compressor. Wear safety glasses and gloveswhen handling refrigerants. Failure to follow this warningcan cause fire, resulting in personal injury or death.CAUTIONDo not manually operate contactors. Serious damage to themachine may result.WARNINGElectrical shock can cause personal injury and death. Shutoff all power to this equipment during installation and ser-vice. There may be more than one disconnect switch. Tagall disconnect locations to alert others not to restore poweruntil work is completed.SEENOTEa38-7315NOTE: See wire color codes inCrankcase Heater Wiring sec-tion, page 146.Fig. 167 — Compressor Junction Box WithoutMotor Protection Module