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Why Is My Air Conditioner Blowing Hot Air? A Michigan Tech Explains

Nothing is worse than feeling warm air coming from your vents on a hot day.

Don’t worry—we’ll help you troubleshoot this frustrating problem.

If your AC is blowing hot air, it’s likely because of:

  1. An incorrect thermostat setting
  2. Low refrigerant levels
  3. Dirty components
  4. Leaky ducts

We’ll go into more detail about each of these problems in more detail.

Need an A/C repair ASAP? Call (248) 644-7810 or contact us today.

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Problem #1: An incorrect thermostat setting

This might be kind of obvious, but before calling a pro, you should check your thermostat to make sure it’s set correctly.

First, make sure your thermostat is set to COOL instead of HEAT. Maybe someone accidentally switched the thermostat to heat mode (or they are playing a mean practical joke), which would explain why you’re feeling hot air.

Make sure your thermostat is set to AUTO instead

Second, verify your fan is set to AUTO instead of ON. When your AC fan is set to AUTO, it will only run while your AC is actively cooling your home’s air. If your AC fan is set to ON, it will run constantly—even when your AC isn’t cooling your home’s air—which could explain why you’re feeling hot air.

Problem #2: Low refrigerant levels

Your air conditioner circulates a substance called refrigerant, which is a liquid/gas designed to remove heat from your home. Refrigerant moves from your indoor AC unit, where it absorbs heat, to the outdoor unit, where it dumps the heat into the outdoor air. The cycle repeats continuously until your home reaches your desired temperature.

So, if your AC system is low on refrigerant, you might notice warm air coming from your vents because less heat is being absorbed and discarded from your home.

Wondering how your AC could be low on refrigerant?

Refrigerant isn’t like gas in a car: your AC system doesn’t use it up over time. The only way to have low refrigerant is if you have a leak somewhere in your system.

Common places for refrigerant leaks include:

  1. The compressor (located inside the outdoor unit)
  2. The evaporator coil (located in the indoor unit)
  3. Refrigerant lines that connect the indoor and outdoor units

Signs you have a refrigerant leak

In addition to the warm air coming from your vents, you’ll also notice signs such as:

  1. Hissing sounds coming from your AC
  2. Water pooled around your indoor unit (frozen evaporator coil)
  3. Higher electric bills

If you notice any of the symptoms above, you’ll need to contact an HVAC professional to visit your home and inspect your air conditioner. If they find a leak, they’ll need to repair it and then add the proper amount of refrigerant to your system again.

Problem #3: Dirty components

Several components in your AC system are regularly exposed to dust and grime. Over time, these components can get so dirty that they restrict how much heat your air conditioner can absorb and dump outside. This issue could explain why you’re feeling hot air.

Three components in your air conditioner are especially prone to get dirty and cause this problem:

  1. The air filter
  2. The condenser (outdoor) unit
  3. The evaporator coil

Let’s look at each of these components in more detail.

Problem #1: Dirty air filter

If your air filter is dirty (like the one in the image below), it blocks air from entering your system to be cooled, which could be contributing to the hot-air issue you’re experiencing.

Clean filter (left) versus dirty filter (right)

What to do: Check your air filter. If it is dirty, replace it with a new one.

Problem #2: Dirty condenser unit

The condenser (outdoor) unit is responsible for releasing all of the heat the refrigerant absorbs from your home’s warm air. If your condenser is dirty, your AC can’t get rid of the heat as well, which leads to warmer indoor temperatures.

What to do: Go outside and look at your outdoor unit. Is anything blocking it, such as shrubbery, sticks or debris? If so, remove those objects. If your outdoor unit looks like it’s covered in a thick layer of dust, contact a professional to clean the condenser coils.

Problem #3: Dirty evaporator coil

The evaporator coil (located in the indoor unit) absorbs the warmth from your home’s air. If it is dirty and moldy, the refrigerant can’t absorb the heat, which leads to higher air temperatures inside.

What to do: Since the evaporator coils are delicate, you should contact a professional to clean them for you.

Problem #4: Leaky ducts

Your air ducts are usually located in unconditioned spaces that get really hot, like an attic.

If you have leaky ducts, this hot air can enter the ductwork and come out of your vents.

Unfortunately, duct leaks are not uncommon. The average house loses up to 30% of its conditioned air to leaks or poorly connected ducts.

Sometimes it is hard to tell if your ducts have leaks because they are not easily visible. However, you might have a duct leak issue if you notice the following signs:

  • High energy bills
  • Dusty rooms and air
  • Rooms with uneven temperatures or a “stuffy” feeling

If you think you have leaky ducts, you’ll need a professional to inspect your ductwork. They will have special equipment that allows them to easily find and repair leaks.

Want a Michigan HVAC pro to fix your AC?

Schedule a repair today

No matter which of these problems you have, we can fix your AC in no time. (Tip: We offer a $15 discount on repairs when you schedule online.)