Lennox Error Code Search

Error code search offers information on the cause of the malfunction and the status of your air conditioner by entering the error code.


  1. This page provides a simple explanation concerning content relating to error codes and their possible causes. Please note that the content may slightly differ depending on the model.

2. It is always advised that you consult with an HVAC repair professional before attempting to provide any repairs yourself.

3. Precision Air assumes no responsibility for any accidents or troubles caused in the disassembly or repair of equipment performed according to the information on this page.

Lennox air conditioner


If molded case circuit breakers or earth leakage circuit breakers have tripped, do not reset the breaker immediately without first checking for any problems with the insulation of equipment.

Resetting breakers without a check of insulation may cause damage to equipment.

Lennox Air Conditioning Codes:



RESULT: EEPROM parameter error

RESULT: Indoor/outdoor units communication protection

RESULT: Zero-crossing signal error

RESULT: Indoor fan speed out of control

RESULT: Open or short circuit of outdoor temperature sensor or outdoor unit EEPROM parameter error

RESULT: Open or short circuit of room or evaporator temperature sensor

RESULT: Outdoor fan speed out of control

RESULT: IBM malfunction or IGBT over-strong current protection

RESULT: Over voltage or too low voltage protection

RESULT: Temperature protection of compressor top

RESULT: Inverter compressor drive error



F1: Return air temperature sensor open/ short-circuited

P6: Drive board communication error

F2: Evaporator temperature sensor open/ short-circuited

H3: Compressor overheating protection

b5: Indoor unit liquid valve temperature sensor open/short circuited

LP: Indoor and outdoor units unmatched

b7: Indoor gas valve temperature sensor open/ short-circuited

dn: Communication line misconnected or expansion valve error

P7: IPM temperature sensor open/short circuited

E7: Running mode conflict

F3: Outdoor ambient temperature sensor open/ short-circuited

Fo: Pump-down

F4: Outdoor unit condenser mid-tube temperature sensor open/short circuited

C5: Jumper error

F5: Discharge temperature sensor open/ short-circuited

H1: Forced defrosting

E6: Indoor and outdoor communication error

Lc: Compressor start-up failure

PL: DC bus under-voltage protection

E4: High discharge temperature protection

PH: DC bus over-voltage protection

E8: Overload protection

U1: Compressor phase current sensing circuit error

E5: Whole unit over-current protection

HE: Compressor demagnetization protection

P5: Over phase current protection

Hc: PFC protection

H7: Compressor desynchronizing

P8: IPM Temperature Protection

H5: IPM Current protection

L9: Over-power protection

Ld: Compressor phase loss/reversal protection

F0: System charge shortage or blockage protection

F8: Frequency restricted/reduced with whole unit current protection

PU: Capacitor charging error

IPM: Frequency restricted/reduced with

En: Current protection

E1: High pressure protection

F9: Frequency restricted/reduced with high discharge temperature

E3: Low pressure protection

FH: Frequency restricted/reduced with anti-freezing protection

LE: Compressor stalling

F6: Frequency restricted/reduced with overload protection

LF: Over-speeding

EU: Frequency restricted/reduced with IPM temperature protection

PF: Drive board temperature sensor error

E9: Indoor unit full water error

P9: AC contactor protection

E2: Anti-freezing protection

PE: Temperature drift protection

PP: AC input voltage abnormal

Pd: Sensor connection protection

U5: Whole unit current sensing circuit error

U3: DC bus voltage drop error

U7: 4-way valve reversing error

L3: Outdoor fan 1 error protection

H6: Motor stalling

LA: Outdoor fan 2 error protection

U8: PG motor zero-crossing protection



Lennox MS8 SERIES AC Error Codes

C5: Indoor control jumper is missing

E0: EEPROM failure

EE: EEPROM failure

E1: Communication failure between indoor unit and outdoor unit

E2: Indoor coil freeze protection – All system functions are terminated except indoor fan

E3: Outdoor coil blockage or low refrigerant due to leak

E4: Discharge line temperature protection

E5: Compressor overcurrent protection

E6: Communication failure between indoor unit and outdoor unit

FH: Anti-freezing upper and lower limit range

FO: Indoor coil is gathering refrigerant

F1: Indoor ambient sensor (RT1) open or short-circuited

F2: Indoor coil sensor (RT2) open or short-circuited

F3: Outdoor ambient sensor (RT4)open or short circuit

F4: Outdoor coil sensor (RT3) open or short circuit

F5: Discharge line sensor (RT5) error

F6: Compressor overload limit issue

F8: High current limit issue

F9: Discharge line temperature too high

HC: Power factor correction protection

H1: Defrosting (heat pump only)

H3: Compressor overload protection sensor (CT1.2) malfunction

H4: Compressor high temperature protection

H5: Intelligent Power Module (IPM) module protection

H6: Indoor fan not communicating

LP: Indoor and outdoor unit mismatch

L3: Outdoor DC fan motor malfunction

L9: Power factor protection

PH: High voltage protection

PL: Low voltage protection


Lennox MPA012S4S-1L AC Error Codes

EO: Outdoor EEPROM error

E2: Communication error between outdoor unit and all indoor units

E3: Communication error between outdoor unit main control and IPM control

E4: Temp sensor error

E5: High or Low voltage protection

E8: Outdoor DC fan speed error

F1: Indoor unit #1 coil outlet temp, sensor error

F2: Indoor unit #2 coil outlet temp, sensor error

F3: Indoor unit #3 coil outlet temp, sensor error

F4: Indoor unit #4 coil outlet temp, sensor error

F5: Indoor unit #5 coil outlet temp, sensor error

F6: Indoor unit #6 coil outlet temp, sensor error

P1: High pressure switch open

P2: Low pressure switch open

P3: Outdoor Compressor current overload sensed

P4: High temperature sensed at compressor discharge line

P5: High temperature sensed at outdoor coil

Lpe: Inverter module (IPM) error


Lennox Universal Mini-Split Error Codes

E0: Indoor unit EEPROM error

E1: Communication error between indoor unit and outdoor units

E3: Indoor fan speed error

E4: Indoor Return air temperature sensor error

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