Carrier Air Conditioner: P4, E4, E1 And Other Error Messages

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Is your Carrier air conditioner acting up and is displaying an error message? And you're wondering, what does it mean? How to fix it? We researched some common error codes of a Carrier air conditioner, and here is what we found. 

Each error message has a meaning that helps users comprehend the issue. Here are some common error codes you can see on a Carrier air conditioner and their meaning: 

  • P4-  Inverter compressor drive error.
  • E4- Open or short circuit indoor room temperature sensor T1.
  • E1-  Communication problem between indoor/outdoor units.

Continue reading to learn more about Carrier air conditioner error codes, what they mean, and how to troubleshoot them.

AC Outside the building with an carrier brand heavy duty, Carrier Air Conditioner: P4, E4, E1 and other Error Messages

What Are Other Common Carrier Air Conditioner Error Messages?

There is a long list of Carrier AC error codes, but here are some that you might encounter: 

Indoor unit:

  • E0- Indoor unit EEPROM parameter error.
  • EC- Refrigerant leakage detection.
  • P6- Voltage protection for the compressor.
  • F4- Error in outdoor unit EEPROM parameter.

Outdoor unit:

  • E3- Problem with communication between IPM board and outdoor mainboard.
  • E8- Outdoor fan speed malfunction.
  • P5- Condenser high-temperature protection.
  • P6- IPM module protection.

Carrier Air conditioner unit at office

What Causes A P4 Error Code In Carrier ACs?

technician repairing and diagnosing air conditioners

As mentioned, if your Carrier air conditioner displays a P4 error code, it means that there is an error in the inverter compressor drive. This error is can either be caused by:

  • outdoor unit board failure;
  • outdoor unit fan motor failure; or
  • compressor failure. 

How To Fix E4 Error Code In Carrier ACs?

Technically, the E4 error isn't even an error. It indeed informs you that your unit is about to defrost. However, this indicates that something has caused your unit to become excessively chilly. A damaged temperature sensor can potentially cause defrost mode.

There is nothing to do when the unit goes into defrost mode. Your system will operate in protected mode until it is safe to use as an air conditioner.

When your air conditioner no longer detects ice on the evaporator coil, it will resume normal operation.

When your air conditioner has an E4 problem, you may do several maintenance tasks to keep it running. These are:

  • Change your AC air filters regularly
  • Ensure you have a sufficient supply of power
  • Clean your AC unit
  • Let a professional HVAC technician check your AC's refrigerant level

What Does E1 Error Code In Carrier Air Conditioner Indicate?

Air conditioning outside the building

For Carrier AC units, the E1 error code indicates something wrong with your indoor/outdoor units' communication. 

Other possible explanations for an E1 error code include:

  • reminder to change the air filter;
  • perform a reset;
  • loose internal connections; and
  • malfunctioning control panel.

How To Fix E1 Error Code?

Wiring mistakes are the root of most communication problems. The communications part of the control circuitry could be damaged if the connection wires are not correctly connected.

To troubleshoot this error, you need to: 

  1. Confirm that the indoor and outdoor units have the same model numbers.
  2. Check the type and gauge of the communication wires that connect the indoor and outside units.
  3. Make sure there aren't any additional parts connecting the interior and outdoor units.
  4. Before turning on the power, double-check the wire connections.
  5. Check that the indoor unit terminals do not have any condensate pumps connected to them.

If all of the aforementioned are in working order, the problem is most likely caused by one or both of the control boards. There is no way to tell which board is faulty on most models. Replacing the control boards one at a time is the best method.

The outdoor board is usually easier to replace, but the indoor board is typically the one that fails. Brownouts, blackouts, voltage spikes, and lightning strikes can all cause damage to these circuit boards.

It is recommended that a surge protector be installed on the circuit that supplies power to this machine.

What Are The Common Problems A Carrier Air Conditioner Encounters?

installation of the air conditioner and connecting electric wires

Here are some  problems you might encounter with your Carrier AC:

  • The unit/system isn't working.
  • Unit not cooling properly.
  • During an operation, the unit comes to a stop.

Now, you may wonder, what causes such problems? And how to solve them? Listed are possible causes as to why your AC unit is having that kind of problem and their solutions:

The Unit/System Isn't Working

Possible Causes:

  • Blown fuse or tripped circuit breaker.
  • Power outage.
  • Too low voltage.
  • An indoor or outdoor unit issue could be indicated by a green or orange LED flashing on and off.


  • Replace the fuse or reset the circuit breaker using the recommended replacement fuse.
  • Restart the operation once the power has been restored.
  • Call a professional HVAC technician.

Unit Not Cooling Properly

Dirty Filter of Air conditioner which causes no air or cool going out from ac

Possible Causes:

  • Clogged filter.
  • Wrongly set the thermostat.
  • There is an open door or window.
  • Outdoor unit is blocked.
  • The fan is turned down to a low setting.
  • Instead of Cool, the operation mode is Fan or Auto.


  • Remove the air filter and clean it.
  • Check the temperature and, if required, reset it.
  • Close any opening.
  • Remove the blockage.
  • Select a higher fan speed.
  • Set the unit's operating mode to Cool or reset it.

During An Operation, The Unit Comes To A Stop

Possible Causes:

  • The Off timer isn't working properly.
  • An indoor or outdoor unit issue could be indicated by a green or orange LED flashing on and off.


  • Restart the mode of operation.
  • Call a professional HVAC technician.

How To Troubleshoot An Air Conditioner?

process of clean and wash the air condition with the high pressure electric pump in the bedroom during hot su

When troubleshooting an AC unit, you must check these things first before calling an HVAC technician:

  1. Thermostat setting;
  2. Air filter;
  3. Refrigerant level;
  4. Electrical panel;
  5. Evaporator coil; and
  6. Condenser unit.

You may ask, what are the things you need to check from the above-mentioned things to help you troubleshoot? And how do you troubleshoot these problems? Here is what you need to know. 

1. Thermostat Setting

When it comes to troubleshooting an air conditioner, the primary control – the thermostat – is frequently the first place to go. Thermostats come in several types, with the most basic types controlling heating and cooling temperatures as well as fan activity.

You'll know that your thermostat is damaged when you notice these symptoms:

  • At times, lukewarm air blows from the registers/vents, while at other times, frigid air blows.
  • Thermostat readings that were higher than predicted.
  • There is no air coming out of the registers or vents.

Before hiring an HVAC technician to repair the problem, check your thermostat if you notice any of the above symptoms in your home.

  • Set the thermostat to cool or auto to switch between cooling and heating as the temperature changes automatically.
  • Change the fan setting to auto so the blower will turn off when the temperature drops below a certain level.
  • Check the temperature setting to ensure it hasn't been changed to a higher setting by someone else.
  • If you have a programmable thermostat, check your "comfort schedule" for any problems and make sure your preset settings still correspond to the times and temperatures you expect.

If the problem is still not solved, contact an HVAC professional for help.

2. Air Filter

Checking for a dirty air filter is the next most common step in AC troubleshooting. Your air conditioning system is more than simply the outside unit on the exterior of your house. An indoor air handler device, commonly a furnace or fan coil, is also included in most systems.

A clogged filter and obstructed airflow might result from a lack of maintenance. These can result in inefficiency, discomfort, or, in the worst-case scenario, system failure.

Make sure the thermostat is set to cool, and the temperature is proper before examining your air filter.

3. Refrigerant Level

Contact your trusted HVAC professional if you suspect low refrigerant levels. A skilled HVAC technician will have the tools and know-how to troubleshoot refrigerant-related issues in an air conditioner. Do not attempt to diagnose refrigerant problems on your own.

4. Electrical Panel

If you have a blown fuse or a tripped circuit breaker, be sure you are comfortable and capable of properly replacing the fuse or resetting the breaker - if not, seek expert help. Keep in mind that electricity can be extremely harmful, even fatal. Do not try to troubleshoot electrical problems on your own.

5. Evaporator Coil

Continuing to run the system with a frozen evaporator coil can result in catastrophic damage and a possibly expensive repair.

When you have a frozen evaporator coil, it is recommended to shut down the system and contact your trusted HVAC professional because the evaporator coil is often not easily accessible. An experienced contractor should do an air conditioner's refrigerant levels troubleshooting.

6. Condenser Unit

Like the evaporator coil, a condensing unit could have an overly filthy coil or refrigerant leakage. A defective compressor, a malfunctioning condenser fan motor, or a faulty run capacitor are all possible problems with the outdoor condensing unit.

The majority of these air conditioner issues necessitate the assistance of a specialist.

Final Thoughts

AC Outside the building with an carrier brand heavy duty


Although there are manuals that come with your air conditioner when you purchase one, it is still best to consult a professional HVAC technician in dealing with error codes. Especially if you are not confident in troubleshooting your air conditioner's issue. 

Before leaving, you can check these articles: 

Air Conditioner Turns Off After 30 Seconds – What's Wrong?

How To Reset A Carrier Furnace

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