HVAC Toolkit

Carrier Error Codes

Complete fault code reference for Carrier mini-splits and air conditioners

E-Series (Sensor Errors)

Code Description Possible Cause Solution
E0 EEPROM parameter error Memory chip failure or corruption Reset power, replace PCB if error persists
E1 Indoor/outdoor communication error Communication wire fault between units Check wiring connections, verify polarity
E2 Zero-crossing detection error Power supply issue or PCB fault Check power supply, replace PCB if needed
E3 Indoor fan motor speed error Fan motor not reaching target speed Check motor, capacitor, and connections
E4 Indoor room temperature sensor error Thermistor open, short, or out of range Check thermistor resistance, replace if faulty
E5 Indoor coil temperature sensor error Evaporator thermistor malfunction Check and replace coil sensor
E6 Outdoor coil temperature sensor error Condenser thermistor malfunction Check and replace outdoor coil sensor
E7 Outdoor ambient temperature sensor error Outdoor ambient thermistor failure Check and replace ambient sensor
E8 Compressor suction temperature sensor error Suction thermistor malfunction Check and replace suction sensor
E9 Compressor discharge temperature sensor error Discharge thermistor failure Check and replace discharge sensor

P-Series (Protection Errors)

Code Description Possible Cause Solution
P0 Inverter module protection IPM fault, overcurrent, or overheat Check compressor, replace outdoor PCB
P1 High voltage protection Input voltage too high Check and correct supply voltage
P2 Low voltage protection Input voltage too low Check power supply, voltage regulator
P3 Compressor current protection Compressor overcurrent detected Check refrigerant charge, compressor
P4 Compressor discharge temperature protection Discharge temp too high (>115°C) Check superheat, charge, restrictions
P5 High pressure protection Head pressure too high Clean condenser, check charge, verify fan
P6 Low pressure protection Suction pressure too low Check for leaks, verify charge
P7 Compressor top temperature protection Compressor shell overheating Check ambient conditions, charge
P8 Outdoor fan motor protection Fan motor overcurrent or locked Check fan motor, clean blades
P9 Compressor current sensor fault CT sensor malfunction Check CT sensor, replace PCB
PA Four-way valve switching fault Reversing valve stuck or coil fault Check valve solenoid, verify operation
PH DC bus voltage high protection Inverter bus voltage too high Check input power, capacitors
PL DC bus voltage low protection Inverter bus voltage too low Check power supply, connections
PU Compressor phase current overload Phase imbalance or overload Check compressor windings, power

F-Series (Function Errors)

Code Description Possible Cause Solution
F0 Refrigerant shortage Low refrigerant charge detected Find leak, repair, and recharge
F1 Indoor coil anti-freeze protection Evaporator freezing detected Check airflow, filter, charge
F2 Outdoor ambient temperature too low Ambient below operating range Use low-ambient kit if needed
F3 Outdoor ambient temperature too high Ambient above operating range Improve outdoor ventilation
F4 Compressor discharge temperature too high Sustained high discharge temp Check charge, superheat, restrictions
F5 Outdoor coil temperature too high Condenser overtemperature Clean coil, check fan operation
F6 Compressor startup failure Compressor failed to start 3 times Check power, capacitor, compressor
F7 Compressor desynchronization Inverter lost sync with motor Reset power, check compressor
F8 Inverter module overheating PCB heat sink too hot Check ventilation, clean PCB area
F9 PFC protection Power factor correction circuit fault Check power supply, replace PCB

H-Series (Hardware Errors)

Code Description Possible Cause Solution
H0 EEV stepper motor fault Electronic expansion valve error Check EEV motor and wiring
H1 Defrost temperature sensor error Defrost sensor malfunction Check and replace defrost sensor
H2 Compressor PFC circuit error Power factor correction fault Replace outdoor PCB
H3 Compressor phase loss Missing phase in compressor circuit Check wiring, contactor, capacitor
H4 High pressure switch open HP switch tripped Identify cause, reset after fixing
H5 IPM over-temperature protection Inverter power module overheating Check ventilation, reduce load
H6 Compressor motor overload Motor thermal overload Check windings, operating conditions
H7 Compressor motor abnormal Motor fault detected Check compressor windings
H8 AC contactor fault Contactor not operating correctly Check contactor coil and contacts

U-Series (System Errors)

Code Description Possible Cause Solution
U0 Low suction pressure Suction pressure below limit Check charge, find leaks
U1 High discharge pressure Head pressure above limit Clean condenser, check fan
U2 Low discharge superheat Liquid flooding to compressor Check EEV, charge, check superheat
U3 Communication error with remote Wired remote communication fault Check remote wiring and connections
U4 Indoor-outdoor unit mismatch Unit pairing configuration error Verify correct model pairing
U5 Condenser temperature abnormal Unusual condenser temperature Check sensors, condenser operation
U6 System refrigerant overcharge Too much refrigerant Recover excess refrigerant
U7 System refrigerant undercharge Insufficient refrigerant Add refrigerant, check for leaks
U8 Outdoor fan speed abnormal Fan not reaching target RPM Check motor, capacitor
U9 Compressor speed abnormal Compressor not reaching target Hz Check inverter, compressor

LED Flash Codes

Code Description Possible Cause Solution
1 Flash Indoor unit PCB fault Main board error Replace indoor PCB
2 Flashes Room temperature sensor open/short Thermistor fault Replace room sensor
3 Flashes Coil temperature sensor open/short Evaporator sensor fault Replace coil sensor
4 Flashes Indoor-outdoor communication error Wiring fault Check communication wiring
5 Flashes High pressure protection HP switch activated Check and fix pressure issue
6 Flashes Low pressure protection LP activated Check refrigerant charge
7 Flashes Compressor overcurrent High amp draw Check compressor condition
8 Flashes Fan motor fault Motor not running Check fan motor
9 Flashes EEPROM error Memory fault Replace PCB

Carrier Error Code Troubleshooting Tips

Reading Error Codes

  • • Error codes display on wired remote or indoor display
  • • LED flash codes on PCB indicate faults when no display
  • • Check outdoor PCB for additional diagnostics
  • • Service mode provides detailed error history

Common Solutions

  • • E1: Communication error - check 3-wire connection
  • • P4/P5: Pressure issues - verify refrigerant charge
  • • F0: Low charge - find and repair leak first
  • • Always power cycle after resolving faults