Carrier WEATHERMAKER 48/50AJ Operation And Service Manual

Also see for 48AJ: Installation, Start-Up and Service Instructions Installation instructions Started guide Operating and service guide

Contents

96A051 (Circuit A, Compressor 1 Stuck On Failure)A052 (Circuit A, Compressor 2 Stuck On Failure)A055 (Circuit B, Compressor 1 Stuck On Failure)A056 (Circuit B, Compressor 2 Stuck On Failure) — Alarmcodes 051, 052, 055, and 056 are for compressors A1, A2, B1,B2 respectively. These alarms occur when the current sensor(CS) detects current when the compressor should be off. Whenthis occurs, the control turns off the compressor and logs a strikefor the respective circuit. Use the scrolling marquee to reset thealarm.If the current sensor board reads ON while the compressorrelay has been commanded OFF for a period of 4 continuousseconds, an alarm is generated. These alarms are only moni-tored for a period of 10 seconds after the compressor relay hasbeen commanded OFF. This is done to facilitate a service tech-nician forcing a relay to test a compressor.In addition, if a compressor stuck failure occurs and the cur-rent sensor board reports the compressor and the request off,certain diagnostics will take place.1. If any of the 4 compressors are diagnosed as stuck on andthe current sensor board is on and the request is off, thecontrol will request the supply fan which will automati-cally start building airflow control. Condenser fans willalso be commanded on to maintain normal head pressure.2. Heating will be disabled while any one of the compres-sors has this problem.The possible causes are:• welded contactor• frozen compressor relay on MBBTo check out alarms 051, 052, 055, and 056:1. Place the unit in Service Test mode. All compressorsshould be off.2. Verify that there is not 24 v at the contactor coil. If there is24 v at the contactor, check relay on MBB and wiring.3. Check for welded contactor.4. Verify CS wiring.5. Return to Normal mode and observe compressor opera-tion to verify that compressor current sensor is workingand condenser fans are energized after compressor starts.T064 (Circuit A Saturated Condensing Thermistor Failure)T065 (Circuit B Saturated Condensing Thermistor Failure) —Alert codes 064 and 065 are for circuits A and B, respectively.This alert code is for 48/50AJ,AK,AW,AY units only. Thesealerts occur when the saturated condensing temperatures (Tem-peraturesREF.TSCT.A and SCT.B) are outside the range–40 to 240 F (–40 to 116 C). When this occurs, the control usesthe outdoor temperature (OAT) to control the outdoor fans. Thecontrol will default to control based on the OAT sensor and willturn on OFC.B when the ambient is above 65 F and off whenthe ambient is below 50 F.If the SCT and OAT sensors have all failed then the controlshould turn on OFC.B when compressors are on.The cause of the alert is usually a faulty thermistor, ashorted or open thermistor caused by a wiring error, or a looseconnection.T072 (Evaporator Discharge Reset Sensor Failure) — If theunit is configured to use the remote EDT 4 to 20 mA reset in-put (ConfigurationEDT.RRES.S) and the sensor readingis less than 2 mA then the alert will occur. When this occurs thecontrol will default to the internal set points. The sensor isconnected to the optional CEM module. For this sensor to beused, the EDT 4 to 20 mA reset input (ConfigurationEDT.RRES.S) must be set to “enabled.”T073 (Outside Air Temperature Thermistor Failure) — Thisalert occurs when the outside air temperature sensor (Temper-aturesAIR.TOAT) is outside the range –40 to 240 F(–40 to 116 C). Failure of this thermistor (Tempera-turesAIR.TOAT) will disable any elements of the controlwhich requires its use. Economizer control beyond the ventposition and the calculation of mixed-air temperature for thesumZ algorithm will not be possible. This alert resets automati-cally. The cause of the alert is usually a faulty thermistor, ashorted or open thermistor caused by a wiring error, or a looseconnection.T074 (Space Temperature Thermistor Failure) — This alertoccurs when the space temperature sensor (TemperaturesAIR.TSPT) is outside the range –40 to 240 F (–40 to116 C). This alert will only occur if the unit is configured to usea space temperature sensor. Configuration is done throughthe Unit Control Type (ConfigurationUNITC.TYP)configuration. Failure of this thermistor (Tempera-turesAIR.TSPT) will disable any elements of the controlwhich requires its use. If the unit is configured for SPT 2 stageor SPT multi-stage operation and the sensor fails, no cooling orheating mode may be chosen. This alert resets automatically.The cause of the alert is usually a faulty thermistor in the T55,T56, or T58 device, a shorted or open thermistor caused by awiring error, or a loose connection.T075 (Return Air Thermistor Failure) — This alert occurswhen the return air temperature sensor (Tempera-turesAIR.TRAT) is outside the range –40 to 240 F (–40 to116 C). The RAT is standard on all units and is located in thereturn section near the auxiliary control box. This alert resetsautomatically. The cause of the alert is usually a faulty thermis-tor, a shorted or open thermistor caused by a wiring error, or aloose connection.Failure of this thermistor (TemperaturesAIR.TRAT)will disable any elements of the control which requires its use.Elements of failure include:• the calculation of mixed air temperature for sumZ control• the selection of a mode for VAV units• economizer differential enthalpy or dry bulb control• return air temperature supply air resetT076 (Outside Air Relative Humidity Sensor Failure) —This alert occurs when the outside air humidity sensor (In-putsREL.HOA.RH) has a reading less than 2 mA. Failureof this sensor will disable any elements of the control which re-quires its use including economizer outdoor and differential en-thalpy control. The OA.RH sensor is located in the economizerhood and is used for control of the economizer. The sensor is aloop powered 4 to 20 mA sensor. This alert resets automatical-ly. The cause of the alert is usually a faulty sensor, a shorted oropen sensor caused by a wiring error, or a loose connection.The unit must be configured to use the sensor through the Out-side Air RH Sensor (ConfigurationECONORH.S)setting.T078 (Return Air Relative Humidity Sensor Failure) — Thisalert occurs when the return air humidity sensor(InputsREL.HRA.RH) has a reading less than 2 mA.Failure of this sensor (InputsREL.HRA.RH) will disableIMPORTANT: If the compressor starts, verify that theindoor and outdoor fans are operating properly.IMPORTANT: If the CS is always detecting current, thenverify that the compressor is on. If the compressor is on,check the contactor and the relay on the MBB. If the com-pressor is off and there is no current, verify CS wiring andreplace if necessary.IMPORTANT: Return to Normal mode and observe com-pressor operation to verify that compressor current sensoris working and condenser fans are energized after compres-sor starts.