Carrier 48/50AJ specifications A051 Circuit A, Compressor 1 Stuck On Failure

IMPORTANT: If the compressor starts, verify that the indoor and outdoor fans are operating properly.

IMPORTANT: If the CS is always detecting current, then verify 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 and replace if necessary.

IMPORTANT: Return to Normal mode and observe com- pressor operation to verify that compressor current sensor is working and condenser fans are energized after compres- sor starts.

A051 (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) — Alarm codes 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. When this occurs, the control turns off the compressor and logs a strike for the respective circuit. Use the scrolling marquee to reset the alarm.

If the current sensor board reads ON while the compressor relay has been commanded OFF for a period of 4 continuous seconds, an alarm is generated. These alarms are only moni- tored for a period of 10 seconds after the compressor relay has been 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 and the current sensor board is on and the request is off, the control will request the supply fan which will automati- cally start building airflow control. Condenser fans will also 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 MBB

To check out alarms 051, 052, 055, and 056:

1.Place the unit in Service Test mode. All compressors should be off.

2.Verify that there is not 24 v at the contactor coil. If there is 24 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 working and 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. These alerts 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 uses the outdoor temperature (OAT) to control the outdoor fans. The control will default to control based on the OAT sensor and will turn on OFC.B when the ambient is above 65 F and off when the ambient is below 50 F.

If the SCT and OAT sensors have all failed then the control should turn on OFC.B when compressors are on.

The cause of the alert is usually a faulty thermistor, a shorted or open thermistor caused by a wiring error, or a loose connection.

T072 (Evaporator Discharge Reset Sensor Failure) — If the unit is configured to use the remote EDT 4 to 20 mA reset in- put (Configuration→EDT.R→RES.S) and the sensor reading is less than 2 mA then the alert will occur. When this occurs the control will default to the internal set points. The sensor is connected to the optional CEM module. For this sensor to be used, the EDT 4 to 20 mA reset input (Configuration →EDT.R→RES.S) must be set to “enabled.”

T073 (Outside Air Temperature Thermistor Failure) — This

alert 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 control which requires its use. Economizer control beyond the vent position and the calculation of mixed-air temperature for the sumZ algorithm will not be possible. This alert resets automati- cally. The cause of the alert is usually a faulty thermistor, a shorted or open thermistor caused by a wiring error, or a loose connection.

T074 (Space Temperature Thermistor Failure) — This alert occurs when the space temperature sensor (Temperatures →AIR.T→SPT) is outside the range –40 to 240 F (–40 to 116 C). This alert will only occur if the unit is configured to use a space temperature sensor. Configuration is done through the Unit Control Type (Configuration→UNIT→C.TYP) configuration. Failure of this thermistor (Tempera- tures→AIR.T→SPT) will disable any elements of the control which requires its use. If the unit is configured for SPT 2 stage or SPT multi-stage operation and the sensor fails, no cooling or heating 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 a wiring error, or a loose connection.

T075 (Return Air Thermistor Failure) — This alert occurs when the return air temperature sensor (Tempera- tures→AIR.T→RAT) is outside the range –40 to 240 F (–40 to 116 C). The RAT is standard on all units and is located in the return section near the auxiliary control box. This alert resets automatically. The cause of the alert is usually a faulty thermis- tor, a shorted or open thermistor caused by a wiring error, or a loose 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 reset

T076 (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. Failure of 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 economizer hood and is used for control of the economizer. The sensor is a loop powered 4 to 20 mA sensor. This alert resets automatical- ly. The cause of the alert is usually a faulty sensor, a shorted or open 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) — This

alert 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 disable

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