Why is my A/C blowing hot air? A Kansas City tech explains!

On a hot day, there’s nothing more frustrating than getting warm air when you’re expecting cool air.

We’ll explain what could be causing this common (and annoying) issue.

If your AC is blowing hot air, it’s usually one of the following problems:

  1. Incorrect thermostat setting
  2. Tripped breaker
  3. Dirty air filter
  4. Dirty outdoor unit
  5. Low refrigerant

Let’s look at each of these issues in more detail…

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Problem #1: Incorrect thermostat setting

We know it may sound silly, but the first thing you should check is your thermostat setting. Make sure your thermostat is set to COOL not HEAT.

COOL vs HEAT setting on a thermostatWe know this sounds obvious, but you never know—someone (your child, your child’s friend or a resentful house guest) may have changed it.You’ll also want to verify the thermostat fan is set to AUTO, not ON. If the thermostat fan is set to ON, the AC blower will run constantly—even if the air isn’t being cooled. That means it will blow cool air sometimes and warm air other times.
Make sure your thermostat is set to AUTO and not ON

Problem #2: Tripped breaker

One explanation for warm air coming from your AC could be a tripped outside breaker.

Your AC system has two breakers: one for the inside unit, another for the outdoor unit.

If the outdoor unit trips, the inside unit will continue to run, but will only blow warm air into your home.


If this is your issue, you can try resetting the circuit breaker. If the outdoor unit keeps tripping, contact a professional for assistance.

Problem #3: Dirty air filter

Another reason your AC could be blowing hot air is because of a dirty air filter.

The purpose of your air filter is to catch particles so that they don’t circulate in your home’s air-stream. Over time, the filter can become clogged with dirt and debris, which limits the airflow coming into your system.

Low airflow prevents your system from cooling air properly, which could lead to warmer air coming from your vents.


Check your air filter. If it is dirty, replace it with a new one.


Problem #4: Dirty outdoor unit

If your outdoor unit (also called the condenser unit) is dirty, then your AC system might be delivering warm air to your home.

In order to understand why, let’s look at how the cooling process works in your AC system, step-by-step:

  1. Your indoor unit sucks warm air from your home and blows it over cool evaporator coils.
  2. The heat is absorbed by refrigerant, a liquid/gas that travels between the indoor and outdoor units of your AC system.
  3. Refrigerant carries this heat out of your home and dumps the heat outside via the outdoor unit.
  4. After dumping the heat outside, the refrigerant returns to the indoor unit and the process repeats itself.

That’s how the cooling process is supposed to work.

However, if your outside unit is covered in dirt, leaves, grass, sticks, etc., then it creates a barrier that makes it harder for the refrigerant to dump heat outside. This could explain why your AC is blowing hot air.


Clear the outdoor unit of any debris (leaves, sticks, etc.). If that doesn’t fix the problem, contact a professional to clean the condenser coils.

Note: We recommend having a trained technician clean the coils because if you aren’t careful, you can easily damage them and make the problem worse.

Problem #5: Low refrigerant

Like we mentioned before, refrigerant is the liquid/gas that absorbs the heat from your air and transfers it outside.

If you don’t have enough refrigerant, then your air conditioner can’t absorb enough heat to properly cool your air.


If you have low refrigerant levels, it most likely means you have a refrigerant leak somewhere in your system. A professional will need to repair the leak and refill your system with the appropriate amount of refrigerant.

WARNING: Don’t have a professional add more refrigerant without finding and repairing the leak FIRST, or you’ll be wasting money. Imagine you have a gas leak in your car. You wouldn’t add more gas without fixing the leak first, right? The same idea applies to fixing refrigerant leaks in your air conditioning system.

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