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Why Is My Central Air Conditioner Not Cooling My House?

We’ll start by saying this: If it’s hot enough to fry an egg on the concrete outside and your air conditioner isn’t cooling your home correctly, you’re in trouble.

So, what’s the deal?

There could be a variety of reasons your AC isn’t cooling your home. Some of the most common reasons include:

  • Incorrect thermostat settings
  • Clogged air filter
  • Dirty outdoor unit
  • Low refrigerant
  • Incorrectly sized system

Some of these issues you can fix on your own, while others you’ll need to schedule an air conditioning technician to diagnose your problem. Let’s start by looking at one of the issues you can fix on your own: your thermostat settings.

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Cooling Issue #1: Incorrect thermostat settings

If the air coming from your vents doesn't feel cool, it could just be your thermostat settings. Our first suggestion: Check your thermostat to make sure it’s on the right settings.

thermostat setting

You’ll want to make sure that your thermostat is set to COOL not HEAT. We know this sounds obvious, but it happens! If your thermostat is accidentally set to “heat” your AC is never going to come on.

In addition to the temperature settings, check the fan settings. There are three options here, ON, OFF and AUTO. You want to make sure the fan is set to AUTO.

fan thermostat setting

If you have it set to “ON” then the indoor blower will continually blow air into your home...even when that air hasn’t been cooled.

If you’ve checked your thermostat and fan settings and they are correct, then you may have a clogged air filter. We’ll dive into that issue, below.

Cooling Issue #2: Clogged air filter

Your air filter works as the barrier between your home’s air and your AC system. When your air filter is dirty or clogged, it blocks air from reaching your indoor AC unit, which makes it harder for your AC to circulate cooled air back into your home.

To see if this is your issue, go to your return vent and check the air filter. Does it look like the one on the right?

clean vs dirty air filter

If so, change it (it should be changed once a month).

To determine if this was your issue, you’ll have to allow your AC system to catch up for a few hours. However, if you’ve replaced your air filter (and waited for a few hours) and your system still isn’t cooling your home, you are likely facing another issue.

Cooling Issue #3: Dirty outdoor unit

When’s the last time you had your outdoor air conditioning unit cleaned? If the answer is never, you may have found your problem.

The outdoor unit of your AC system needs to be clean and clear of obstructions (grass, bushes, tree branches, fences) so it can release heat from your home’s air into the outdoor air. When it’s dirty, clogged or blocked, it’s unable to release this heat outside, which means the air circulating inside your home will not be as cold as you need it to be.

As a general rule of thumb, you need to clean your outdoor unit at least once a year.

While you can clean the outdoor unit yourself, doing it properly requires a professional touch (and most professionals will clean it as part of an AC maintenance visit).

dirty ac condenser

If your AC looks like the unit above and you live in the Phoenix area, contact us to clean your outdoor AC unit.

Cooling Issue #4: Low Refrigerant

Your AC system actually cools your home’s air by removing the heat from that air. It does this by absorbing that heat via a substance called refrigerant. If your AC system is low on refrigerant, it’s unable to absorb as much heat as it needs to, resulting in higher temperatures in your home.

If your system is low on refrigerant, there is likely a leak in the refrigerant line that a professional will need to repair or replace. To fix this, you’ll need to contact a professional. If you live in Phoenix, we can help you. Contact us!

Cooling Issue #5: Incorrectly sized system

If you’ve exhausted this entire list of potential issues, your AC system may simply be too small for your home.

We know this isn’t the answer you want to hear, but if your system is too small for your space, it will continue to struggle to cool your home when it’s hot outside, regardless of what you do.

When you had your AC system installed, an HVAC tech should have performed a series of calculations called a load calculation, which determines what size of AC system is right for your home. If they didn’t do this, or simply came up with the wrong numbers, you could have a system that is too small to support cooling your home.

Our suggestion would be to contact that contractor or company that installed your AC system and speak with them. If you recently purchased your AC system, a replacement may be covered in your warranty.

If not, you should consider hiring an experienced technician to help you determine what size AC IS right for your Phoenix home, so you aren’t left with a warm home (and increased energy bills) for the entire lifetime of your AC system.

Ready for cool air again? Call Phoenix’s best: George Brazil

We’ve been keeping Phoenix-area homes safe, comfortable and energy-efficient since 1955.

If you can’t figure out why your AC isn’t cooling your home, we’d be happy to come and check it out for you.