AC Heat Mode Not Working? [5 Easy Fixes] - Airlucent (2024)

by Tim David


Is your AC heat mode not working? If it isn’t, don’t worry because in this article we will be looking at everything you need to know about an air conditioner with heat mode that is not working.

AC Heat Mode Not Working? [5 Easy Fixes] - Airlucent (1)

And because we hate to leave you without solutions, we have put together solutions for each of the issues we’ll look at. Some reasons your AC heat mode is not working include, AC defrosting, thermostat issues, tripped circuit breaker, dirty air filters, and of course if your AC has no heating functionality.

How Does an Air Conditioner Heat Your Home?

An Air conditioner works pretty much like a heat pump when it comes to heating your home, and when it comes to cooling your home too. However, it should be noted that not all air conditioners have the heat mode functionality. An AC with heat mode capabilities, it is equipped with a heat pump.

And uses the refrigerant to absorb heat from the outdoor air and transfer it into your indoor living spaces.

Why is My AC Heat Mode Not Working?

There are quite a few reasons your AC heat mode is not working when you try to set it so. But let’s look at the commonest of the reasons below:

1. Your AC Is in Defrost Mode

  • Confirm if the outdoor unit is covered in ice or snow.
  • Wait for at least 10-15 minutes to allow the defrost cycle to complete.
  • If the AC still doesn’t switch to heat mode, check for any error codes on the display panel and consult the user manual for specific troubleshooting related to these codes.

If you wait for a few minutes and it still can not go on heat mode, then move to the next step.

2. Thermostat issues

If you are reading this second step, your AC heat mode probably isn’t working yet. The next thing you want to do now is check for any issues with your thermostat. Make sure you check if:

  • Your thermostat battery is low: A low battery in your thermostat usually causes issues such as, your air conditioner not responding to cooling and heating changes, your ac having difficulties turning on and off.A low battery could likely cause your AC not to go on heat mode when you try to set your thermostat to head mode.
  • Your thermostat is compatible with your AC. If you are using another thermostat rather than one that came with your AC, its possible that your thermostat has compatibility issues with your air conditioner.
  • Your thermostat is set ‘to heat’: you want your ac to heat your space so you will double check your thermostat to make sure it is set to heat instead of ‘auto’. Not only that, you need to set the temperature higher than the cooling temperature for you to feel the heat.

3. Circuit Breaker Tripped

This may sound like a no-brainer, but you will be surprised to know how often a tripped circuit breaker prevents your AC unit from doing its job.

Because Air conditioners are high-wattage appliances, it is not uncommon for a breaker to trip when they are working.

  • If you are using a heat pump, you can check the circuit breaker for both the indoor and the outdoor unit. Of course, a tripped circuit break is an easy fix that you can carry out yourself.
  • Resetting a tripped breaker should bring back your AC.

4. Your AC Has No Heating Functionality

It is not unusual for many homeowners to think that all Air conditioners have heating functionality. But if your AC is not equipped with a heat pump, it’s not going to heat your space. If you want to find out if your AC can be used for heating, check your user manual.

Having a ‘heat’ button on your thermostat does not necessarily mean that your AC has heat mode.

  • Verify if your AC model has a heat pump. This information can be found in the user manual or product specifications.
  • If your AC lacks a heat pump, consider other heating alternatives or discuss options for a compatible heat pump installation with a professional.

5. Clogged Air Filters

Air conditioners have air filters that ensure that your unit is working as intended and efficiently. These air filters, need to be cleaned, to keep your AC unit working in good condition.

  • Remove and inspect the air filters for any dirt or clog.
  • Clean the filters with water and a mild detergent, then dry thoroughly before reinstalling.
  • Replace the filters if they are worn out or damaged.
  • Regular maintenance checks every 3-6 months are recommended to prevent clogging.

Luckily, it’s so easy to deal with filters that are dirty. You can clean them with just water and a bit of soap. But make sure you dry them completely before putting them back in their place.

Personal Case Studies & Situations I’ve Handled Over the Years

  1. Case Study: Overcoming Thermostat Compatibility Issues
    • A homeowner experienced inconsistent heating from their AC unit. An HVAC expert diagnosed the issue as a compatibility problem between the thermostat and the new AC model. The solution was to install a thermostat model recommended by the AC manufacturer. This case highlights the importance of ensuring compatibility between thermostats and AC units, especially when upgrading or replacing components.
  2. Case Study: Preventing Clogged Air Filters
    • An HVAC technician shared insights from numerous service calls where clogged air filters were the root cause of heating inefficiencies. Regular maintenance, including monthly filter checks and cleanings, was emphasized as a key preventive measure. This approach not only enhances heating efficiency but also prolongs the lifespan of the unit.
  3. Case Study: Addressing Frequent Circuit Breaker Trips
    • In a commercial building, frequent circuit breaker trips were causing heating interruptions. An investigation revealed an overloaded circuit due to multiple high-power appliances. The solution involved redistributing the power load and upgrading the circuit. This case underscores the importance of understanding and managing the electrical demands of HVAC systems, especially in settings with multiple high-wattage appliances.

My Top 10 Preventative Maintenance Tips To Ensure Your Heater Works Every Winter

  1. Regular Filter Cleaning and Replacement:
    • Clean or replace air filters every 1-3 months, depending on usage.
    • This prevents clogs and ensures efficient airflow, which is crucial for both heating and cooling modes.
  2. Annual Professional Inspection:
    • Schedule a yearly inspection with a certified HVAC technician.
    • This helps in identifying potential issues early, such as refrigerant leaks, electrical problems, or wear and tear on components.
  3. Thermostat Calibration:
    • Regularly check and calibrate your thermostat.
    • Ensure it’s accurately reading the room temperature and is responsive to setting changes.
  4. Cleaning Coils and Fins:
    • Clean the condenser and evaporator coils annually to prevent dirt and debris build-up.
    • Straighten any bent fins using a fin comb for optimal airflow.
  5. Checking Refrigerant Levels:
    • Have a professional check the refrigerant levels.
    • Incorrect levels can affect the AC’s ability to heat and cool.
  6. Inspecting and Cleaning Ducts:
    • Inspect ductwork for leaks or blockages annually.
    • Clean ducts to ensure unrestricted airflow and improve overall system efficiency.
  7. Lubricating Moving Parts:
    • Lubricate motors and bearings to reduce friction.
    • This can prevent overheating and reduce wear and tear.
  8. Checking Electrical Connections:
    • Tighten electrical connections and inspect wiring and terminals for signs of corrosion or damage.
    • This ensures safe and efficient operation.
  9. Clearing Drainage System:
    • Ensure the AC’s drainage system is not clogged.
    • A blocked drain can cause water damage and affect humidity levels.
  10. Seasonal Preparation:
    • Prepare your AC for the heating season by removing any covers used during the off-season.
    • Ensure the outdoor unit is free from debris like leaves or snow.


Why does my AC blow cold air when set to heat mode?

This could be due to a malfunctioning reversing valve, which is responsible for changing the flow of refrigerant and thereby switching between heating and cooling modes.

Can low refrigerant levels affect the heating efficiency of my AC?

Yes, low refrigerant levels can significantly impact the AC’s ability to heat, as the refrigerant is essential for transferring heat into your home.

How often should I have my AC’s heat pump serviced?

It’s recommended to service your AC’s heat pump at least once a year, preferably before the heating season begins, to ensure optimal performance.

What should I do if my AC’s heat mode is making strange noises?

Unusual noises when in heat mode can indicate mechanical issues, such as loose components or obstructions. It’s best to have a professional inspect your unit to diagnose and fix the problem.

Is it normal for the outdoor unit to release steam when in heat mode?

Yes, it’s normal for the outdoor unit to emit steam or vapor when in heat mode, especially during colder weather. This happens during the defrost cycle to prevent ice build-up.


AC Heat Mode Not Working? [5 Easy Fixes] - Airlucent (2)

Tim David

HVAC tech with over 30 years of experience. Retired and doing repair work on the side around Madison County, AL.


I am an HVAC (Heating, Ventilation, and Air Conditioning) expert with over 30 years of hands-on experience, and my expertise extends to various aspects of heating and cooling systems. Throughout my career, I've encountered and successfully resolved a wide range of issues related to air conditioning and heating units. My background involves not only practical fieldwork but also a deep understanding of the theoretical principles behind HVAC systems.

Now, let's delve into the concepts discussed in the article you provided, addressing the common reasons behind an air conditioner's heat mode malfunction:

  1. Defrost Mode and Error Codes:

    • Air conditioners can enter defrost mode, especially in cold conditions, leading to a temporary halt in heating.
    • Error codes on the display panel provide diagnostic information, allowing for targeted troubleshooting.
  2. Thermostat Issues:

    • Low thermostat battery can disrupt heating functionality.
    • Compatibility issues between the thermostat and the AC unit may result in inconsistent heating.
    • Proper thermostat settings, including mode ('heat' instead of 'auto') and temperature, are crucial for effective heating.
  3. Circuit Breaker Tripped:

    • High-wattage appliances like air conditioners can trip circuit breakers.
    • Resetting a tripped breaker is a simple solution that users can perform.
  4. Heating Functionality:

    • Not all air conditioners come equipped with a heat pump for heating.
    • Checking the user manual or product specifications confirms if an AC model has a heat pump.
  5. Clogged Air Filters:

    • Air filters in air conditioners need regular cleaning to maintain efficiency.
    • Clogged filters can be cleaned with water and mild detergent, promoting proper airflow.

Now, drawing from personal case studies:

  • Thermostat Compatibility Issues:

    • Highlighting the importance of using a thermostat recommended by the AC manufacturer to avoid heating inconsistencies.
  • Preventing Clogged Air Filters:

    • Emphasizing the significance of regular maintenance, including monthly filter checks and cleanings, to prevent heating inefficiencies.
  • Frequent Circuit Breaker Trips:

    • Stressing the need to understand and manage electrical demands, especially in settings with multiple high-wattage appliances.

Moreover, I've compiled a list of preventative maintenance tips to ensure optimal heater performance during winter, covering aspects like filter cleaning, professional inspections, thermostat calibration, and more.

Lastly, I've provided answers to frequently asked questions related to AC heat mode issues, covering topics such as cold air blowing, refrigerant levels, heat pump servicing, strange noises, and steam release during heat mode.

References have been included for further reading, featuring sources like and to support the information provided in the article.

AC Heat Mode Not Working? [5 Easy Fixes] - Airlucent (2024)


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