Carrier 38MGQ Series Service Manual

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Carrier 38MGQ Series Service Manual Manual pdf 31 page image

31SYSTEM EVACUATION ANDCHARGINGUNIT DAMAGE HAZARDFailure to follow this caution may result in equipmentdamage or improper operation.Never use the system compressor as a vacuum pump.CAUTION!Refrigerant tubes and indoor coil should be evacuated using therecommended deep vacuum method of 500 microns. Always breaka vacuum with dry nitrogen.SYSTEM VACUUM AND CHARGEUsing Vacuum Pump1 Completely tighten all flare nuts and connect manifold gagecharge hose to a charge port of the low side service valve.(See Fig. 27.)2 Connect charge hose to vacuum pump.3 Fully open the low side of manifold gage (see Fig. 28).4 Start vacuum pump5 Evacuate using the triple evacuation method.6 After evacuation is complete, fully close the low side ofmanifold gage and stop operation of vacuum pump.7 The factory charge contained in the outdoor unit is good forup to 25ft. (8 m) of line length. For refrigerant lines longerthan 25ft. (8 m), add refrigerant as specified in theADDITIONAL REFRIGERANT CHARGE table in thisdocument.8 Disconnect charge hose from charge connection of the lowside service valve.9 Fully open service valves B and A.10 Securely tighten caps of service valves.Outdoor Unit Indoor UnitRefrigerantService ValveLow SideHigh SideABCDFig. 27 – Service ValveManifold Gage500 micronsLow side valve High side valveCharge hose Charge hoseVacuum pumpLow side valveFig. 28 – ManifoldDeep Vacuum MethodThe deep vacuum method requires a vacuum pump capable ofpulling a vacuum of 500 microns and a vacuum gage capable ofaccurately measuring this vacuum depth. The deep vacuum methodis the most positive way of assuring a system is free of air andliquid water (see Fig. 29).500MINUTES0 1 2 3 4 5 6 710001500LEAK INSYSTEMVACUUM TIGHTTOO WETTIGHTDRY SYSTEM2000MICRONS250030003500400045005000Fig. 29 – Deep Vacuum GraphTriple Evacuation MethodThe triple evacuation method should be used. Refer to Fig. 30 andproceed as follows:1 Pump system down to 500 MICRONS of mercury andallow pump to continue operating for an additional 15minutes. Unit must maintain 500 microns or less for 30minutes or more to ensure a dry system.2 Close service valves and shut off vacuum pump.3 Connect a nitrogen cylinder and regulator to system andopen until system pressure is 2 psig.4 Close service valve and allow system to stand for 10minutes. During this time, dry nitrogen will be able todiffuse throughout the system absorbing moisture.5 Repeat this procedure as indicated in Fig. 30. System willthen be free of any contaminants and water vapor.CHECK FOR TIGHT, DRY SYSTEM(IF IT HOLDS DEEP VACUUM)EVACUATEBREAK VACUUM WITH DRY NITROGENWAITEVACUATERELEASE CHARGE INTO SYSTEMBREAK VACUUM WITH DRY NITROGENEVACUATEWAITFig. 30 – Triple Evacuation MethodFinal Tubing CheckIMPORTANT: Check to be certain factory tubing on bothindoor and outdoor unit has not shifted during shipment.Ensure tubes are not rubbing against each other or any sheetmetal. Pay close attention to feeder tubes, making sure wire tieson feeder tubes are secure and tight.