Carrier Air Conditioners & Heat Pumps

The system has detected that the incoming line voltage has dropped below 180V AC RMS at any time, or below 185V AC RMS for more than 5 seconds. The unit will not operate or will shut down to protect components. This fault clears when voltage rises above 187V.

The system has detected that the incoming line voltage has risen above 285V AC RMS at any time, or above 280V AC RMS for more than 5 seconds. The unit will not operate or will shut down to protect electronic components. This fault clears when voltage drops below these thresholds.

The Bluetooth module fails to send periodic status messages to the PCM (control board) for 2 consecutive minutes after unit power-up. This means the service app will not be able to connect to the unit. The fault clears when a single good message is received.

The equipment is reducing compressor speed to prevent ice from forming on the indoor coil, as indicated by the saturated suction temperature approaching 32°F. This is a protective measure to ensure proper operation.

The 5V DC power supplied from the PCM to the VFD through the communication harness is interrupted or out of range. If this voltage is not restored, the system will shut down. This 5VDC is shared with pressure transducers.

A valid model plug value is stored in the PCM's memory, but the physical model plug is not currently installed. The equipment will operate properly if the stored model plug value corresponds to the equipment model.

This code indicates that the model plug currently installed is different from the one the system previously recognized. It will set when the equipment is powered on with a different valid model plug, or if the plug is changed while the unit is operating.

The system requires a specific model plug to identify its size and type, enabling the PCM software to apply correct operating limits. This code indicates that the installed model plug is invalid and does not match any recognized models, preventing the unit from operating.

A valid model plug was not present when the equipment was powered up, and there is no valid model plug value stored in the PCM's memory. The equipment will not operate and is locked out. A new model plug will not be acknowledged while power is applied.

This code is generated when the system recognizes the physical model plug but finds it incompatible with the installed Variable Frequency Drive (VFD). This mismatch will prevent the system from operating.

This fault indicates that the microcontroller on the installed PCM (Processor Control Module) board is an older version than required. Boards with this fault should not be used in operation.

This code signifies that an attempt for the PCM (Processor Control Module) to reprogram itself was unsuccessful. If this message is not recent, a subsequent reprogramming attempt might have succeeded automatically.

The PCM (Processor Control Module) stores vital equipment configuration data in its non-volatile EEPROM memory. This code indicates a failure in writing information to this memory, which can only be resolved by replacing the PCM.

This code appears if Fuse 1 on the PCM board is blown or missing. Fuse 1 powers important components like the PEV, RVS, and Bluetooth module; these will not function. AC units may operate partially, but heat pump units will be completely inoperable.

This code is set if Fuse 2 on the PCM board is blown or missing. Fuse 2 specifically powers the LLS (Liquid Line Solenoid). When this fault is active, the entire system will not operate.

The system detects excessively high discharge pressure, leading to either compressor speed reduction (31-11) or a system shutdown and 2-hour lockout (31-58 if at minimum speed). The system attempts to self-correct by reducing compressor speed over time.

This fault means the 670psi high pressure switch has activated, safely disabling system operation. It can occur due to rapid pressure spikes or a fault in the high-pressure switch's wiring harness during high-pressure events. The system will not attempt to restart until discharge pressure drops below 425 PSIG.

This fault occurs when the discharge pressure is too high (above 620 psig) to safely start the compressor. The system will remain inoperable until the refrigerant pressures drop to an acceptable range. This can often be caused by extremely high ambient temperatures.

The system has detected low suction pressure, exceeding its soft or hard limits, leading to a shutdown (32-15). Four occurrences of 32-15 result in a 2-hour lockout (32-55). The system will attempt to restart after a 5-minute delay.

The suction pressure in the refrigeration system is too low to safely start the compressor, causing the system to be inoperable. It will remain inoperable until pressures increase to an acceptable range.

The compressor's discharge pressure has dropped below the lower safe operating limit for a period of time, causing the system to shut down. This fault applies to 5-ton models. Repeated occurrences can lead to a lockout (Code 33-55).

This lockout occurs after 6 instances of 'Code 33-15 Compressor Low Discharge Shutdown' within a 2-hour period. The system will be locked out for 2 hours.

The compressor's discharge temperature has exceeded 230°F. The system will reduce capacity by 25% on the next startup to mitigate this. Each hour of operation without faults will gradually restore capacity. Continuous high temperatures can lead to a lockout.

This lockout occurs when the discharge temperature exceeds 230°F while the system is already running at minimum capacity due to previous high temperature events. The system will shut down for 2 hours.

The system has detected a high compression ratio that cannot be adjusted by Automatic Envelope Management (AEM). The next startup will operate at a 25% reduced capacity. Each hour of operation without faults will gradually restore capacity. Repeated occurrences can lead to a lockout.

This lockout occurs when the high compression boundary is crossed while the system is already running at minimum capacity due to previous high compression events. The system will shut down for 2 hours.

The system has detected a low compression ratio that cannot be adjusted by Automatic Envelope Management (AEM), causing a shutdown. Before this fault, AEM attempts to increase compression ratio by reducing outdoor fan speed (cooling only) and then increasing compressor speed. Repeated occurrences can lead to a lockout.

This lockout occurs after 4 instances of 'Code 36-15 Compressor Low Compress Shutdown' within a 2-hour period. The system will be locked out for 2 hours.

The VFD (Variable Frequency Drive) has detected additional compressor starting failures. While active, the unit opens the PEV (Pressure Equalization Valve) to equalize pressure and attempt retries. Three consecutive occurrences lead to a lockout (Code 38-53).

The compressor is prevented from starting because the pressure differential is too high (above 100psi) and the PEV (Pressure Equalization Valve) was unsuccessful in lowering it. This protects the compressor. The fault clears once the pressure differential is below 100psi.

The VFD Estimator, used in the compressor starting process, has encountered a fault. While active, the PEV will open and the compressor will continue attempts at restarting. Three continuous occurrences will result in a lockout (Code 38-71).

This lockout occurs after 3 consecutive 'Code 38-13 VFD Compressor Fault - Start Fail' events. The system will be locked out for 2 hours. This indicates significant compressor starting issues.

The compressor is running at over 400rpm but fails to increase the pressure differential (discharge pressure - suction pressure) by at least 20psi within 30 seconds. This locks operation for 30 minutes.

This lockout occurs after three continuous 'Code 38-31 VFD Compressor Fault - Estimator' events. The system will be locked out for 4 hours. This typically indicates high starting torque or potential compressor damage.

The fan attempted to start but did not achieve the commanded speed. The system tried to restart the fan multiple times.

The fan's actual speed does not match the commanded speed, either spinning too slow when asked to speed up, or spinning when commanded to be off.

The fan was running above a certain speed but then unexpectedly slowed down or stopped. This causes the compressor and fan to shut down temporarily.

The fan failed to start after multiple attempts and the system has entered a lockout state for one hour. This is a more severe version of Code 39-13.

The fan unexpectedly shut down multiple times, causing the system to lock out. This indicates a persistent problem with the fan operation.

The system's Variable Frequency Drive (VFD) is not receiving feedback from the fan motor, or there's a large speed error. The system is locked out for 30 minutes.

The system initiated a defrost cycle but could not reach the target coil temperature within the maximum allowed time. This suggests heavy icing or a sensor issue.

The Pressure Equalization Valve (PEV) opened to balance pressures but failed to reduce the pressure difference below 40psi within 10 minutes. This won't prevent startup but may cause other faults.

The Outdoor Air Thermistor (OAT) sensor circuit is open, meaning its resistance is too high. The system will use the Outdoor Coil Thermistor (OCT) instead and limit performance.

The Outdoor Air Thermistor (OAT) sensor circuit is shorted, meaning its resistance is too low. The system will use the Outdoor Coil Thermistor (OCT) instead and limit performance.

The Outdoor Coil Thermistor (OCT) sensor circuit is open, meaning its resistance is too high. Defrost cycles will always run for the maximum time.

The outdoor coil thermistor, which is used to monitor the coil during defrost, is reporting a resistance below 1kohm for 1 second, indicating a short circuit. When this fault is active, defrost cycles will occur for their maximum programmed duration. This fault does not lead to a system malfunction.

The outdoor suction thermistor (OST) is detected as 'open' (resistance above 465kohm). This sensor is crucial for controlling the outdoor EXV in heat pump systems, so heating mode will be locked out. Cooling operation may still be permitted, but a malfunction will display on the wall control, often showing '47'.

The outdoor suction thermistor (OST) is detected as 'shorted' (resistance below 1kohm). Similar to an 'OST Open' fault, heating mode operation in HP systems will be locked out. Cooling operation may still be allowed, but the wall control will display a malfunction, often showing '47'.

The discharge thermistor (ODT), essential for compressor protection and ensuring discharge superheat, is detected as 'open' (resistance above 310kohm). When this malfunction is active, the system will only run at startup speed, and '47' may be substituted for its value.

The discharge thermistor (ODT) is detected as 'shorted' (resistance below 670 ohm). Similar to 'ODT Open,' the system will only run at startup speed, and '47' may be substituted for its value. Normal operation will resume once a valid ODT value is read by the PCM.

This fault indicates that the signal wire for pressure transducer P1 (codes 57-xx) or P2 (codes 58-xx) is 'open,' meaning it's returning more than 4.5V DC. This typically occurs if the sensor wire is disconnected, causing the PCM to pull the signal voltage to +5V DC.

This fault indicates that the signal wire for pressure transducer P1 (codes 57-xx) or P2 (codes 58-xx) is 'shorted,' meaning it's returning less than 0.5V DC. The most common cause is the sensor wire shorting to the metal chassis of the unit.

This code signifies that pressure transducer P1 (57-43) or P2 (58-43) is sending an incorrect DC voltage value (specifically 4.84-4.95V DC) to the PCM, indicating a likely failure of the transducer part itself. The system will enter a lockout state.

The system's Variable Frequency Drive (VFD) control relay coil is detected as shorted to ground, making the system inoperable. The VFD will not be powered.

The Power Factor Correction (PFC) circuit in the VFD has exceeded a peak current limit while driving the compressor. The system will shut down and attempt to restart.

The current in the Power Factor Correction Module (PFCM) circuits is unbalanced, applicable to 4 and 5 ton models with multiple reactors. The VFD will shut down and attempt to restart.

The Power Factor Correction (PFC) circuit in the VFD exceeded its peak current limit multiple times, leading to a system lockout for 4 hours. A power cycle can clear the timer.

The current in the Power Factor Correction Module (PFCM) circuits was unbalanced multiple times, leading to a system lockout for 4 hours. This applies to 4 and 5 ton models.

The Variable Frequency Drive (VFD) senses that one or more compressor wires are not connected, making the system inoperable.

The Variable Frequency Drive (VFD) is monitoring input current and has limited or reduced the compressor speed because the current rose above a safe threshold.