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  • Writer's picture338 Aircon

Why Your Aircon Unit Is Blowing Warm Air

An aircon unit blowing warm air is not all that uncommon aircon issue. Unlike most fairly innocent issues, an aircon unit blowing warm air is quite alarming.

Essentially, the aircon unit should be blowing cold air. That’s pretty much its main job. When a unit starts blowing warm air, you have to shut it off and fix it immediately. That means that you first have to diagnose why your aircon unit is blowing warm or even hot air.

The air that comes out of an aircon unit or indoor air handler is cold because it passes through cooling coils or refrigerant coils. If your home aircon unit is blowing warm it when on cold setting, it basically comes to this reasons:

When the cooling system’s filter is clogged, the aircon unit cannot properly move air through the system. This aircon issue strains your aircon unit and can cause warm air to blow.

Pro 338 Reminder: One thing that can restrict airflow severely enough are clogged air filters. If air filters are clogged, the airflow will be reduced drastically, and every part of your aircon unit will try to overcompensate for the lack of airflow mainly because its goal is to achieve a low temperature, as set by the thermostat.

When determining what’s wrong when your aircon unit isn’t properly cooling your home, first check your aircon unit filters to ensure it is clean. If the existing air filter is dirty, replace it with a new, clean filter to see if the warm aircon issue resolves.

Your aircon unit’s evaporator coils extract heat from the home’s air to start the cooling process. A bi-product of this process is condensation, which is why aircon units have a drip pan and condensate drain to catch the extracted moisture and move it out of the system. When moisture collects on the evaporator coils, they may freeze. Frozen coils prevent heat transfer, so you’ll feel warm air blowing from your aircon unit if this problem is present.

Check for this aircon issue by shutting off power to your aircon unit and opening the access door to interior system components, which allows you to assess the evaporator coils. If you see frost or ice on the coils, the best option is to give the coils time to thaw as this can take up to 24 hours depending on the severity of the freeze. Leave your aircon unit off and do not run it again until the coils have thawed.

Pro 338 Tip: A heat gun or hairdryer can also be used to thaw coils that have iced over. Carefully pass the heat over the ice to thaw the coils. Make sure the system’s drip pan and condensate drain are not clogged so they are able to effectively remove this moisture. If you’re uncomfortable performing these tasks, a professional aircon servicing company will be happy to make any necessary repairs.

Frozen evaporator coils can be caused by poor airflow, refrigerant leaks, system damage, or other issues. The root of the issue must be resolved to prevent a recurring aircon issue.

Sometimes, a simple mistake at the thermostat can lead to an aircon unit not providing enough cold air. If the blower fan is set to ON instead of AUTO, it runs all the time, not just during a cooling cycle. In between cooling cycles, the air you feel from the vents can be warm.

Check your thermostat’s settings if you have an aircon unit that’s blowing hot air. Ensure the fan is set to AUTO and the COOL setting is selected.

Pro 338 Tip: The bigger issue is with new thermostats. If your new aircon unit is blowing warm air, there is a chance that the thermostat is not wired properly. The improperly wired thermostat is quite a mess; a mess which may lead to some unusual things like warm air coming from your aircon unit.

However, this is only applicable to new or newly wired air conditioners. If your aircon unit was working normally before, it should work normally now. The chance of a wire slipping from the thermostat socket, for example, is minuscule.

Electric aircon issues can also cause your aircon unit to blow warm air. The first thing to do is quite basic; check all the outlets and cables. That’s usually fine.

One thing we might forget and may lead to warm air coming from your aircon unit is blown fuses and tripped amp breakers.

Both fuses and amp breakers are used to protect our aircon unit from electrical surges. In case there is anything wrong with them, blown fuse or tripped amp breaker, then you might be seeing some weird consequence. Warm air blowing from your aircon unit is one of them.

Pro 338 Reminder: Do check if your aircon unit fuse was blown or if the amp breaker is tripped. Both are quite easily fixable.

Refrigerant leaks are also a reason why your aircon unit might be blowing warm air. When refrigerant escapes the system via a leak, the aircon unit doesn’t have the proper charge to complete its cooling cycles. Thus, the air you feel indoors is warmer than it should be.

Unfortunately, refrigerant leaks must be corrected by a professional aircon servicing company with the proper certifications for refrigerant handling. Other signs that point to a refrigerant leak include:

  1. Frozen evaporator coils

  2. Hissing noises from air conditioner components

  3. Higher electric bills without explanation

Pro 338 Reminder: When an aircon unit is blowing warm air, the most common cause is low freon levels. Due to the lack of freon, the freon expansion (turning it from liquid to gas) is not sufficient. That means the cooling coil will not be adequately cooled and in fact, it might start to become warmer the longer we run the aircon unit.

Why are refrigerant levels too low? There is only one reason for freon levels being too low; a leak in your refrigerant lines. And since refrigerant lines are a closed system, therefore no freon goes in or out if your aircon unit is operating normally. Leaks in refrigerant lines are not all that uncommon. Unfortunately, in many cases, you will need to contact a professional aircon servicing company to fix the leak and refill the refrigerant.


It’s always a good time to talk about the common issues that aircon units have. This way, you’ll be able to spot if there are problems with your unit or not and prepare for its replacement accordingly. If you require our aircon servicing services, Whatsapp us at +65 9222 4141 for a fast and transparent quote.

338 Aircon Servicing Singapore provides an extensive range of Aircon Services including Aircon Servicing, Aircon Repairs, Aircon Installation of the best aircon brands, Chemical Overhaul, Gas Top-up, Aircon Leaking Water, and Aircon Not Cold Fix, and more. We have a team of professional technicians who are equipped with vast knowledge and experience in the Aircon industry.

We have over 15 years of experience in dealing with aircon works and have completed thousands of aircon works for both residential (Landed, Condo, and HDB) and commercial. We are a highly recommended Aircon Company in Singapore, with many delighted customers and reviews over the years on Google and Facebook.

WhatsApp us at +65 9222 4141 for a transparent quotation and honest pricing for all your aircon needs or Call us at +65 9222 4141. We offer a fast and efficient service to serve any of your aircon needs!


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