34 Lennox Air Conditioner Error Codes + troubleshooting

Table of Contents

Lennox air conditioner error codes can be tricky for everyone. Especially when you do not know what the error code means and why it is caused, you won’t be able to solve it.

But don’t worry! We are here to help you out. In this guide, you will find all the error codes of Lennox air conditioners along with their causes and effective solutions.

Lennox AC error code F1 (Indoor ambient temperature sensor is short-circuited)

Status of AC:

In the case of error code F1, the unit stops operation once it reaches the temperature point.

During the drying and cooling operations, all other loads stop operating except the IDU fan motor.

During the heating operations, the entire system halts its operations.

Cause of error:

There are 4 reasons why this error occurs:

  1. If the main board is broken.
  2. If the wiring terminal between the main board and the indoor ambient temperature sensor is too loose or poorly connected.
  3. If the indoor ambient temperature sensor is damaged.
  4. If there is a short circuit caused by a trip-over of controller parts.

Solution advice:

If the wiring terminal between the main board and the temperature sensor is too loose or poorly connected, you should connect it properly.

If the error is not fixed, check if there is a short circuit due to a trip-over of the parts. If yes, fix it.

If the error remains, check if the temperature sensor is normal. If it is not, then replace the temperature sensor.

However, if no solution is working, then replace the main board with the same model.

Lennox AC error code F2 (Indoor evaporator temperature sensor is short-circuited)

Status of AC:

In error code F2, the unit stops operation once it reaches the temperature point.

During the drying and cooling operations, all other loads stop operating except the IDU fan motor.

During the heating operations, the entire system halts its operations.

Cause of error:

Here are 4 causes of this error:

  1. If the main board is broken.
  2. If the wiring terminal between the main board and the indoor evaporator temperature sensor is too loose or poorly connected.
  3. If the indoor evaporator temperature sensor is damaged.
  4. If there is a short circuit caused by a trip-over of controller parts.

Solution advice:

Check if the wiring terminal between the main board and the temperature sensor is connected properly.

If the error is not fixed, check if there is a short circuit due to a trip-over of the parts. If there is, fix it.

If the error remains, check if the temperature sensor is normal. If it is not, then replace the temperature sensor.

However, if no solution is working, then replace the main board with the same model.

Lennox AC error code H6 (IDU fan motor blocked protection)

Status of AC:

In error H6, the electric heat tube, ODU fan, IDU fan, and compressor stop operating. The horizontal louver also stops at the current position.

Cause of error:

Here are 5 causes of this error:

  1. The motor is malfunctioning.
  2. The main board is broken.
  3. The fan blades are not rotating smoothly.
  4. The feedback terminal of PG has a loose connection.
  5. The control terminal of the PG motor has a loose connection.

Solution advice:

Turn off the air conditioner and use a tool to stir the blades of the fan to check if they are rotating smoothly. If they are not, try reassembling the shaft and motor bearing rubber base and also the blades to ensure there are no foreign objects stuck in there.

If the fan blades are okay and the error does not go away, check the connection of the PG motor feedback terminal and make sure it is firm.

Check the connection of the control terminal of the PG motor and make sure it is firm.

Power ON the unit and check if the control terminal of the PG motor has a voltage above 50V within one minute after the opening of the louvers. If yes, check if the motor is started up. In case the motor has not started, you will have to replace the PG motor. But if the motor has started and the voltage is also above 50V it means there is no problem here.

Now the last option is to replace the main board with a similar model.

Lennox AC error code C5 (Protection of jumper cap malfunctioning)

Status of AC:

In this error, the unit does not act. However, the control panel and remote controller operations are available.

Cause of error:

  1. If the controller is damaged.
  2. If the jumper cap is damaged.
  3. If the jumper cap is inserted improperly.
  4. If the jumper cap is not present on the main board.

Solution advice:

First, you need to make sure you have a jumper cap on the main board. If there is none, get one and assemble it.

If you have a jumper cap, make sure it is properly connected.

If the error does not go away, replace the jumper cap with the same model. If the error appears again, replace the main board with the same model.

Lennox AC error code E5 (over-current protection)

Status of AC:

During the drying and cooling operations, all other loads stop operating except the IDU fan motor.

During the heating operations, the entire system halts its operations.

Cause of error:

  1. If the voltage supply is unstable.
  2. If the load is too high but the supplied voltage is too low.
  3. If the air inlets and outlets are blocked or the heat exchangers (indoor and outdoor) are very dirty.
  4. If the fan motor stops working. The speed of the fan is too slow or the fan doesn’t run at all.
  5. If the compressor is malfunctioning. The temperature of the shell is too high or there is oil leakage and abnormal sounds.

Solution advice:

Make sure the voltage supply is stable and within the normal range.

Clean the air inlets and outlets, outdoor and indoor heat exchangers, and remove any blockages in them.

If the fan does not move or its speed is too slow, check the motor and try reinstalling it to fix the problem.

Measure how much current is there in the live wire of the main board. If it does not exceed the over-current protection value, replace the main board with the same model.

If there are blockages in the system, use high-pressure nitrogen to flush the heat exchangers and open the blockages.

If the compressor is not functioning normally and there are abnormal sounds, oil leakages, or the shell temperature is too high, you should replace the compressor.

Otherwise, if no solution works, replace the main board with a similar model.

Lennox AC error code E8 (Overload malfunction)

Status of AC:

The error code E8 causes the entire unit to stop working.

Cause of error:

  1. If the indoor and outdoor heat exchanger is very dirty or if the air inlets and outlets are blocked.
  2. If the fan does not move at all or the fan speed is too slow.
  3. If the compressor does not work normally. There are abnormal sounds and oil leakages. The casing temperature is too high.
  4. If the system is blocked due to ice, dirt, or oil. The Y-valve might not be open completely.
  5. The temperature sensor on the main board is detecting things wrongly.

Solution advice:

Make sure that the outdoor ambient temperature is within the normal range.

Make sure the outdoor and indoor fans are working normally. If not, check their capacitor and connection and fix if there’s anything wrong with them.

Lennox AC error code U8 (Zero-crossing inspection circuit)

Status of AC:

The unit does not act. But the operations of the control panel and remote controller are available.

Cause of error:

  1. When the zero-crossing inspection circuit of the main board for the controller is abnormal.
  2. When the electric discharging of the capacitor is low and it causes wrong judgment by the controller. Quick energization and de-energization.

Solution advice:

Turn OFF the power and turn it ON after 1 minute.

If the error code U8 appears again, it means the zero-cross detection circuit of the main board is abnormal. Replace the main board with a similar model in such a case.

Lennox AC error code H3 (overload of compressor)

Status of AC:

Error code H3 causes the entire unit to stop.

Cause of error:

  1. If the indoor and outdoor heat exchanger is very dirty or if the air inlets and outlets are blocked.
  2. If the fan does not move at all or the fan speed is too slow.
  3. If the compressor does not work normally. There are abnormal sounds and oil leakages. The casing temperature is too high.
  4. If the system is blocked due to ice, dirt, or oil. The Y-valve might not be open completely.
  5. If the refrigerant is leaking and causing overheating protection to the compressor.
  6. If the high-pressure switch is abnormal.

Solution advice:

  1. Clean the indoor and outdoor heat exchangers and the air inlets and outlets.
  2. If the fan is not moving or is slow, check the motor and reinstall it to fix the problem.
  3. Fix the compressor if it is making abnormal noises or causing leakages or the temperature of the shell is too hot.
  4. If the system is blocked due to ice, oil, or dirt, then remove the blockages.
  5. If the high-pressure switch is abnormal, replace it.
  6. If the refrigerant is leaking, fix it.

If no solution works, replace the main board with the same model.

Lennox AC error code F0 (lack of refrigerant)

Status of AC:

Error code F0 causes the whole system to stop. It indicates a lack of refrigerant, overload protection compressor, or block protection for the system.

Cause of error:

  1. When there is a refrigerant leak.
  2. When the unit is plugged up somewhere.
  3. When the indoor evaporator temperature sensor does not work normally.
  4. When the outdoor working condition is too high but the power voltage is too low. So the compressor cannot be started normally.

Solution advice:

Find out why the refrigerator is leaking and fix the leakage. After that, charge the refrigerant to fix the problem.

If the problem remains, clean the indoor & outdoor heat exchangers and air inlets and outlets. Remove any blockages.

Make sure the compressor works normally.

Lennox AC error code E1 (high-pressure protection)

Status of AC:

During the drying and cooling operation, all the loads stop operating except the indoor fan.

During heating operation, the inverter unit stops completely, whereas, the floor-standing unit also stops completely but the operations of the remote controller and control panel are available.

Cause of error:

  1. The main board and display panel are not connected properly.
  2. The HPP terminal on the main board is not connected properly to the high-pressure switch on the main board.
  3. The wiring of the high-pressure switch is too loose.
  4. If the refrigerant is superabundant.
  5. When there is poor heat exchange due to a bad radiating environment and blocked heat exchangers.
  6. When the ambient temperature is too high and the high-pressure protection is caused by over-current protection.
  7. When the supply voltage is not normal.
  8. If the air cycle is short-circuited and the air intake and discharge at the outdoor/indoor heat exchangers are not smooth.
  9. When the heat exchange and filters of outdoor/indoor units are blocked.
  10. If the system pipeline is blocked.
  11. If the liquid valve and gas valve for the outdoor unit is not completely opened.
  12. If the HPP input is at a high level.

Solution advice:

Make sure the main board and display panel are connected properly.

Make sure the HPP terminal on the main board is properly connected to the high-pressure switch.

If the wiring of the high-pressure switch is loose, connect it properly as per the circuit diagram. But if the high-pressure switch is broken, replace it.

If the refrigerator is superabundant, adjust its volume as per the requirements of the system.

If the heat exchange is poor, adjust and improve the performance of the heat exchange.

If the ambient temperature is too high, decrease it.

Make sure the voltage supply is normal. Under normal conditions, the fluctuation should be within 10% of the rated voltage.

Make sure there are no blockages in the pipeline, heat exchanger, and filter of the unit.

Make sure the liquid valve and outdoor gas valve are open completely.

If no solution works, replace the controller to solve the problem.

Lennox AC error code EE (EEPROM failure)

Cause of error:

Error code EE means the EEPROM of your air conditioner has failed.

Solution:

Replace the outdoor control to solve the problem.

Lennox AC error code E2 (Indoor coil freeze protection)

Status of AC:

In error E2, all the functions of the system are terminated excluding the indoor fan.

The RT2, indoor coil sensor monitors the temperature of the coil continuously. When the coil temperature goes below 30.2°F or (-1°C), the outdoor fan and compressor are switched off after 30 seconds.

When the compressor is OFF for at least three minutes and the indoor coil temperature goes above 42.8°F (6°C), the condition is cleared.

Solution:

Check if the indoor airflow is restricted.

Replace the filter if necessary.

Check if the flow of refrigerant is restricted.

Check if the indoor system load or the outdoor ambient temperature is low.

Lennox AC error code E3 (outdoor coil blockage)

Status of AC:

In error E3, all the system functions stop except the indoor fan.

It occurs when the outdoor coil is blocked or when there is low refrigerant due to a leak.

 Solution:

Make sure there are proper clearances around the outdoor unit.

Check the outdoor coil and clean it properly.

Lennox AC error code E4 (discharge line temperature protection)

Status of AC:

The RT5 sensor monitors the discharge line temperature of the compressor and then communicates with the microprocessor of the outdoor unit.

Now the compressor will either continue to run at the current rate or its speed will be increased depending on the measured temperature.

The compressor will be de-energized if the temperature is too high. Once the discharge temperature of the compressor drops below 90°C or 1&4°F, the unit resumes its normal operations.

Solution:

Check if there is a low refrigerant charge.

Check if the refrigerant flow is restricted due to blocked capillaries.

Lennox AC error code E6 (Communication failure between indoor and outdoor unit)

Status of AC:

After 3 minutes of delay, all the system functions stop except the indoor fan.

Solution:

If you see the error code on the outdoor unit, check the communication wires of the outdoor and indoor units and make sure their connection is firm.

Lennox AC error code FH (Anti-freezing lower and upper limit range)

Status of AC:

The compressor runs at a lower speed until the temperature rises.

Solution:

Wait till the temperature goes above 42.8°F (6°C) and then recheck the operation status.

Lennox AC error code FO (Indoor coil is gathering refrigerant)

Status of AC:

All the functions of the system except the indoor fan are terminated.

Solution:

First, you need to pump the refrigerator into the outdoor unit.

Now check the 2-way shut-off valve and see if its flow is restricted or if it is closed. Correct it accordingly.

Lennox AC error code F3 (Outdoor ambient sensor RT4 short circuit or open)

Status of AC:

All the functions of the system except the indoor fan are terminated.

Solution:

Check the sensor and make sure it is in the acceptable range.

Check the proper resistance of the sensor.

If the sensor is open, out of calibration, or sorted, replace it.

Lennox AC error code F4

Cause of error:

When the outdoor coil sensor is short-circuited, open, or out of calibration, the error code F4 occurs.

Lennox AC error code F5 (discharge line sensor error)

Status of AC:

The indoor fan continues running whereas all other system functions run for 3 minutes and then terminate.

Solution:

Check the sensor and make sure it is in the acceptable range.

Check the sensor for proper resistance.

If the sensor is open, out of calibration, or sorted, replace it.

Lennox AC error code F6 (compressor overload limit issue)

Status of AC:

The system continues to run, however, its compressor speed remains reduced until you fix the issue.

Solution:

The outdoor ambient air temperature might be too high so please check it.

Check if the compressor rotor is locked.

Check if the refrigeration circuit is blocked, for example, the capillary tubes.

Check if the outdoor airflow is blocked or restricted. Make sure to remove any blockages.

Check if the refrigerant charge is low.

Lennox AC error code F8 (High current limit issue)

Status of AC:

The system continues to work but at a lower compressor speed until you fix the issue.

Solution:

Check if the input voltage is too high or too low and fix it if necessary.

Lennox AC error code F9

Cause of error:

The error code F9 appears when the discharge line temperature is too high.

Solution:

Check the discharge line temperature and correct it if too high.

Lennox AC error code HC (Power factor correction protection)

Status of AC:

In this error, the system works at a lower compressor speed until you fix the underlying problem.

Lennox AC error code H1 (defrosting)

Status of AC:

The system continues to work normally.

Solution:

Normal defrost operation can solve the problem.

Lennox AC error code H3 (Malfunction of compressor overload protection sensor)

Status of AC:

The indoor fan continues to work while the rest of the system functions are terminated.

Solution:

Check the wiring and connections of the outdoor control input plug (CT1, 2) and make sure everything is properly connected.

Check the overload protection sensor terminals mounted at the top of the compressor and look for continuity across it.

Lennox AC error code H4 (Compressor high-temperature protection)

Status of AC:

The indoor fan continues to work while the rest of the system functions are terminated.

Solution:

Check the wiring and connections of the outdoor control input plug (CT1, 2) and make sure everything is properly connected.

Check for continuity across the overload protection sensor terminals located at the top of the compressor.

Lennox AC error code H5 (Intelligent power module protection)

Cause of error:

The problem can be caused due to the following reasons:

  1. If the voltage is low.
  2. If the ambient temperature is high.
  3. Due to loss of cooling to the heat sink.
  4. When the outdoor control is fastened to the heat sink because of loose screws.

Lennox AC error code H6 (Indoor fan stops communicating)

Status of AC:

This error leads to the termination of all the system functions.

Solution:

The error might be caused due to indoor motor failure or indoor control failure.

Check the wiring between the terminal mark of the fan and the fan motor and ensure that it is properly connected.

Check the wiring between the indoor control and the fan motor to make sure it is not too loose and properly connected.

Replace the wiring if damaged

Lennox AC error code LP (Outdoor and indoor unit mismatched)

Cause of error:

This problem occurs when two components of the system are mismatched.

Solution:

Check and make sure that the red jumper on the indoor control board is in the right place.

Lennox AC error code L3 (Malfunction of outdoor DC fan motor)

Cause of error:

If the outdoor DC fan motor of your air conditioner is not working due to any reason, it leads to error code L3.

Solution:

Check the wiring between the outdoor control terminal and the fan motor. Make sure all the wiring connections are connected properly and there is nothing damaged or too loose.

If there is nothing wrong with the wiring, replace the DC fan motor to solve the problem.

Lennox AC error code L9 (Power factor protection)

Cause of error:

This error occurs when there is a low or high input voltage condition in the indoor unit.

Solution:

Make sure the input voltage at terminals N1 and 3 is proper and normal.

Lennox AC error code PH (High voltage protection)

Status of AC:

This error causes the termination of all the functions of the system.

Solution:

Check the input voltage on the N and L terminals and the outdoor unit terminal strip. Make sure it is stable and normal.

If the voltage is above 265VAC, remove the power supply and fix the input voltage problem before powering ON the unit again.

If the voltage is lower than 265VAC, check the capacitor when the unit is powered OFF. If the voltage is between 200V to 208V, it means that the capacitor is working properly. But if it is not, replace the capacitor.

If the capacitor and input voltage are fine, replace the outdoor control to fix the problem.

Lennox AC error code PL (Low voltage protection)

Status of AC:

This error causes the termination of all the functions of the system.

Solution:

Check the input voltage on the N and L terminals and the outdoor unit terminal strip. Make sure it is stable and normal.

If the voltage is lower than 150VAC, restart the unit and check the power again. For 208 to 230 VAC systems (9-12 kBtu), check the choke (reactor line) connection on the outdoor control terminal AC-L2.

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