Armstrong Air
Armstrong Air Air Conditioners Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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E0
Outdoor unit will not run, thermostat calling for cooling, indoor blower may run but condenser is completely off
Communication Fault Between Indoor and Outdoor Control Boards
E1
Outdoor unit runs briefly then shuts down, status LED on control board flashes E1, cooling is intermittent
High Pressure Switch Open
E2
Outdoor unit will not start, control board shows E2, compressor and fan remain off even though thermostat is calling
Low Pressure Switch Open
E3
Outdoor unit attempts to start, then shuts down with E3 indication, compressor is hot to the touch
Compressor Overload / High Discharge Temperature
E4
Outdoor unit runs but indoor temperature does not drop, control board shows E4, suction line may be very cold or frosted
Evaporator Coil Temperature Sensor Fault / Freeze Protection Trip
E5
Outdoor unit does not start, control board indicates E5, indoor blower may run normally
Outdoor Ambient Temperature Sensor Fault
E6
Outdoor unit starts and stops repeatedly, E6 code logged, compressor may not start reliably
Compressor Start Failure / Locked Rotor Protection
E7
Outdoor unit runs but indoor blower does not, or blower runs at incorrect speed, E7 logged on communicating systems
Indoor Blower Motor Communication / ECM Fault
E8
System shuts down during operation with E8 indicated, may coincide with very low indoor airflow and coil icing
Indoor Coil Airflow Fault / Blower Overcurrent
E9
System will not run in cooling, E9 code present on communicating thermostat or board, other functions may be locked out
Configuration / Setup Error in Communicating System
F1
Indoor unit control board flashes F1, blower may not start or runs erratically in cooling mode
Indoor Control Board Fault / EEPROM Error
F2
Indoor unit flashes F2, cooling may be locked out, thermostat may show indoor temperature error
Indoor Temperature Sensor / Thermistor Fault
F3
Indoor unit flashes F3, blower may shut down during cooling, coil may be very cold
Evaporator Coil Sensor Fault / Freeze Protection
F4
Indoor unit flashes F4, blower may run but cooling is disabled, thermostat may show system fault
High Temperature Limit / Supply Air Overheat in Cooling
F5
Indoor unit flashes F5, system may short-cycle or lock out, thermostat may show communication error
Thermostat Communication Fault (Communicating Systems)
H0
Outdoor unit does not enter defrost in heat pump mode (for Armstrong Air heat pump models), H0 code or similar displayed
Defrost Control Fault
H1
Heat pump frequently enters defrost or stays in defrost too long, H1 or similar code logged
Defrost Sensor Out of Calibration / Shorted
L1
Outdoor unit completely dead, L1 or line-voltage fault indicated on control board, no LED activity
Line Voltage Loss or Phase Fault (for 3‑phase commercial Armstrong Air units)
L2
Outdoor unit intermittently shuts down, L2 or low-voltage fault indicated, thermostat may go blank
Low Voltage (24 VAC) Supply Fault
Symptom
Burning or electrical smell from indoor or outdoor unit during cooling
Overheating Electrical Component
Symptom
Indoor blower does not run in cooling, outdoor unit runs normally
Indoor Blower Motor Not Operating
Symptom
Indoor blower runs but outdoor fan does not, compressor may or may not run, unit hums
Condenser Fan Motor Failure
Symptom
Indoor coil repeatedly freezes into a block of ice during cooling
Evaporator Coil Freeze-Up
Symptom
Indoor temperature varies widely between rooms during cooling
Uneven Cooling / Air Distribution Problem
Symptom
Indoor unit produces a musty or moldy odor when cooling starts
Biological Growth on Evaporator Coil or Drain Pan
Symptom
Indoor unit runs but water leaks from around the air handler or furnace during cooling
Condensate Drain Backup / Pan Overflow
Symptom
Loud buzzing or chattering noise from outdoor unit contactor area
Contactor Chatter / Coil Voltage Instability
Symptom
Outdoor unit hums loudly but compressor does not start, then shuts off on overload
Compressor Hard Start / Locked Rotor
Symptom
Outdoor unit makes loud grinding or squealing noises during operation
Mechanical Noise from Condenser Fan or Compressor
Symptom
Outdoor unit runs but air from indoor vents is warm or only slightly cool
Loss of Cooling Capacity
Symptom
Outdoor unit runs continuously and does not shut off even when thermostat is satisfied
Stuck Contactor or Control Signal
Symptom
Outdoor unit vibrates excessively and is very noisy during operation
Excessive Vibration / Mounting Issues
Symptom
Outdoor unit will not start at all, indoor blower runs and thermostat appears normal
Outdoor Unit No-Start
Symptom
System frequently trips the main breaker when starting or during operation
Overcurrent / Electrical Overload
Symptom
System short-cycles, turning on and off frequently without reaching set temperature
Short Cycling
Symptom
System will not start after a power outage, even though power has been restored
Post-Outage Lockout / Brownout Protection
Symptom
Thermostat display is blank and system does not respond
Thermostat Power Loss
Symptom
Water dripping from supply registers or sweating on ductwork during cooling
Ductwork Condensation
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| E0 |
Outdoor unit will not run, thermostat calling for cooling, indoor blower may run but condenser is completely off
|
Communication Fault Between Indoor and Outdoor Control Boards | View Details |
| E1 |
Outdoor unit runs briefly then shuts down, status LED on control board flashes E1, cooling is intermittent
|
High Pressure Switch Open | View Details |
| E2 |
Outdoor unit will not start, control board shows E2, compressor and fan remain off even though thermostat is calling
|
Low Pressure Switch Open | View Details |
| E3 |
Outdoor unit attempts to start, then shuts down with E3 indication, compressor is hot to the touch
|
Compressor Overload / High Discharge Temperature | View Details |
| E4 |
Outdoor unit runs but indoor temperature does not drop, control board shows E4, suction line may be very cold or frosted
|
Evaporator Coil Temperature Sensor Fault / Freeze Protection Trip | View Details |
| E5 |
Outdoor unit does not start, control board indicates E5, indoor blower may run normally
|
Outdoor Ambient Temperature Sensor Fault | View Details |
| E6 |
Outdoor unit starts and stops repeatedly, E6 code logged, compressor may not start reliably
|
Compressor Start Failure / Locked Rotor Protection | View Details |
| E7 |
Outdoor unit runs but indoor blower does not, or blower runs at incorrect speed, E7 logged on communicating systems
|
Indoor Blower Motor Communication / ECM Fault | View Details |
| E8 |
System shuts down during operation with E8 indicated, may coincide with very low indoor airflow and coil icing
|
Indoor Coil Airflow Fault / Blower Overcurrent | View Details |
| E9 |
System will not run in cooling, E9 code present on communicating thermostat or board, other functions may be locked out
|
Configuration / Setup Error in Communicating System | View Details |
| F1 |
Indoor unit control board flashes F1, blower may not start or runs erratically in cooling mode
|
Indoor Control Board Fault / EEPROM Error | View Details |
| F2 |
Indoor unit flashes F2, cooling may be locked out, thermostat may show indoor temperature error
|
Indoor Temperature Sensor / Thermistor Fault | View Details |
| F3 |
Indoor unit flashes F3, blower may shut down during cooling, coil may be very cold
|
Evaporator Coil Sensor Fault / Freeze Protection | View Details |
| F4 |
Indoor unit flashes F4, blower may run but cooling is disabled, thermostat may show system fault
|
High Temperature Limit / Supply Air Overheat in Cooling | View Details |
| F5 |
Indoor unit flashes F5, system may short-cycle or lock out, thermostat may show communication error
|
Thermostat Communication Fault (Communicating Systems) | View Details |
| H0 |
Outdoor unit does not enter defrost in heat pump mode (for Armstrong Air heat pump models), H0 code or similar displayed
|
Defrost Control Fault | View Details |
| H1 |
Heat pump frequently enters defrost or stays in defrost too long, H1 or similar code logged
|
Defrost Sensor Out of Calibration / Shorted | View Details |
| L1 |
Outdoor unit completely dead, L1 or line-voltage fault indicated on control board, no LED activity
|
Line Voltage Loss or Phase Fault (for 3‑phase commercial Armstrong Air units) | View Details |
| L2 |
Outdoor unit intermittently shuts down, L2 or low-voltage fault indicated, thermostat may go blank
|
Low Voltage (24 VAC) Supply Fault | View Details |
| – |
Burning or electrical smell from indoor or outdoor unit during cooling
|
Overheating Electrical Component | View Details |
| – |
Indoor blower does not run in cooling, outdoor unit runs normally
|
Indoor Blower Motor Not Operating | View Details |
| – |
Indoor blower runs but outdoor fan does not, compressor may or may not run, unit hums
|
Condenser Fan Motor Failure | View Details |
| – |
Indoor coil repeatedly freezes into a block of ice during cooling
|
Evaporator Coil Freeze-Up | View Details |
| – |
Indoor temperature varies widely between rooms during cooling
|
Uneven Cooling / Air Distribution Problem | View Details |
| – |
Indoor unit produces a musty or moldy odor when cooling starts
|
Biological Growth on Evaporator Coil or Drain Pan | View Details |
| – |
Indoor unit runs but water leaks from around the air handler or furnace during cooling
|
Condensate Drain Backup / Pan Overflow | View Details |
| – |
Loud buzzing or chattering noise from outdoor unit contactor area
|
Contactor Chatter / Coil Voltage Instability | View Details |
| – |
Outdoor unit hums loudly but compressor does not start, then shuts off on overload
|
Compressor Hard Start / Locked Rotor | View Details |
| – |
Outdoor unit makes loud grinding or squealing noises during operation
|
Mechanical Noise from Condenser Fan or Compressor | View Details |
| – |
Outdoor unit runs but air from indoor vents is warm or only slightly cool
|
Loss of Cooling Capacity | View Details |
| – |
Outdoor unit runs continuously and does not shut off even when thermostat is satisfied
|
Stuck Contactor or Control Signal | View Details |
| – |
Outdoor unit vibrates excessively and is very noisy during operation
|
Excessive Vibration / Mounting Issues | View Details |
| – |
Outdoor unit will not start at all, indoor blower runs and thermostat appears normal
|
Outdoor Unit No-Start | View Details |
| – |
System frequently trips the main breaker when starting or during operation
|
Overcurrent / Electrical Overload | View Details |
| – |
System short-cycles, turning on and off frequently without reaching set temperature
|
Short Cycling | View Details |
| – |
System will not start after a power outage, even though power has been restored
|
Post-Outage Lockout / Brownout Protection | View Details |
| – |
Thermostat display is blank and system does not respond
|
Thermostat Power Loss | View Details |
| – |
Water dripping from supply registers or sweating on ductwork during cooling
|
Ductwork Condensation | View Details |
No matching codes found
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