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Why Is My AC Blowing Warm Air? What to Check

Why Isn't My AC Blowing Cold Air? What to Check, How to Prevent It

Possible reasons why your AC blows warm air are:

  1. Thermostat is damaged
  2. Thermostat is set incorrectly
  3. Clogged air filter
  4. Clogged drain
  5. Dirty Compressor
  6. Low Refrigerant

Why Is My AC Blowing Cold Air? What to Check, How to Prevent It.

My System Isn’t Blowing Cool Air
Call Us About Your AC System

It gets hot enough in Elgin, East Dundee, and throughout the Fox River Valley in the summer. The last thing you need is warm air blowing out of your air conditioner.

It’s a problem people call us about fairly often during the summer. You may notice it the first time you turn it on. Or, the problem may start later in the season.

Either way, Compass Heating & Air has you covered.

In this blog, we’ll go over the possible causes. You can fix some of these yourself. We’ll also give you some tips on how to prevent it from happening.

That way, you can prepare your system before you need it.

Thermostats and Central Air Problems

The first thing to check is your thermostat. Sometimes, the problem is as simple as having it set for winter.

Make sure the display reads “Cool” rather than “Heat.” Also, set the fan to “Auto.”

This way, your system knows to bring the temperature down, not up. And, it runs whenever the indoor temperature is hotter than the setting.

Try changing the battery as well. Sometimes these units malfunction on low power.

Your thermostat is your first stop when diagnosing this problem. With any luck, you’ll feel the difference a few minutes after making that change.

If not, check your air filter next. We’ll go into that in a bit. If neither of those solves the problem, it’s time to call a professional.

Along with the system, they’ll likely check the thermostat, too. Occasionally, there’s a calibration or sensor issue.

Dirty or Clogged Components

Various parts of your central air system can become dirty or clogged over time. When this happens, one of the symptoms is often the unit producing hot air instead of cooling. Three common culprits are the:

  1. Air Filter
  2. Drain
  3. Compressor

Air Filter

Changing your air filter is simple, but can go a long way.

A dirty or clogged air filter is a simple problem. It’s also one you can — and should — fix yourself.

The filter is in place to block dust and other small contaminants from circulating through your home and HVAC system. But, you’re supposed to change it at least every three months.

When you don’t, it becomes clogged. That’s when the problems begin.

When the filter’s blocked up, it prevents air from flowing through the system properly. That means it may not be removing heat as it should.

Or, it’s so clogged that it trips a failsafe that some units have. If there’s a problem with circulation, the AC shuts down to prevent damage.

In that case, you may still have some air coming through the vents. But, the system didn’t cool it first.

The solution is simple: Change out that air filter like clockwork every three months. And, make sure you have a new one before summer begins.


Your AC uses a drain line to get rid of all the moisture it removes from the air. The water vapor in your home will condense back into liquid when it cools, and the drain gets rid of it.

But, it’s possible for that line to get clogged with dust or other contaminants.

When that happens, you may get an algae buildup in there. Once that crucial part of the system gets blocked up, it causes problems elsewhere.

And, often, that results in warm air coming through your vents.

You can look up DIY ways to clean it out. But, we recommend professional service. You don’t want to damage anything or cause more contaminants to flow through your system.

Schedule A Service For Your AC
How to Choose The Right Air Filter


Finally, there’s the dirty compressor. This problem can occur if there’s a lot of lawn debris or trash near your unit.

It’s a common problem because most people don’t think much about their AC during the off-season. But, that’s when leaves, grass, dirt, or litter can build up around the outdoor compressor.

At this point, a few things may go wrong.

Things could be as simple as those items building up around the compressor. When that happens, air can’t get through the fins to do the job.

In that case, it’s as simple as clearing things away before the season.

However, they can also make their way into the system. It happens either by clogging the fins you can see from the outside. Or, trash can fall in from the top around the fan.

Those spots are tricky to clean without damaging something. You also want to look out for mold or other growths from organic materials.

Low Refrigerant

If your air conditioner is low on refrigerant, then it can’t cool the air passing through it. This can happen if there’s a leak somewhere in the line. And, if you’ve had your air conditioner for less than ten years, it’s a fairly straightforward fix.

We’d find the leak, repair it, and recharge the system.

However, systems built before 2010 use R22 Freon. And, the EPA has banned the production of it. So, there’s not a lot left, and what’s out there is getting expensive.

We covered this topic in-depth here. But, the summary is that we usually recommend replacement if there’s a significant refrigerant loss on an older unit.

Adding coolant to your system can become very expensive.

Cooling Hot Problem Rooms in the Summer
Will A Service Plan Save You Money?

How To Prevent Your AC From Blowing Cold Air

There are a few things you can do to prevent your AC from blowing cold air:

  • Check Your Thermostat
  • Change Your Air Filter
  • Get Your Air Conditioner Tuned Up

We’ve gone over those first few items already. So, let’s talk about preventative maintenance.

Air Conditioner Tune-Ups

An air conditioner tune-up is a professional inspection and cleaning of your system. It’s the best way to make sure your cooling system is ready for the hard work ahead of it.

A technician will check dozens of points along the way to make sure every component is optimized. If there’s a problem with the fan, the compressor, the drain, or anything else, they’ll spot it during the inspection.

This process heads off all those problems you can’t fix or locate yourself. And, overall, it makes sure your AC works great and uses as little energy as possible to do the job.

If you’re having trouble with your air conditioner, or you want to take some simple steps to ensure a cool, comfortable summer, call or email us here at Compass Heating & Air.

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  1051 E. Main St., Suite 106  •  East Dundee, IL 60118  | 
  (630) 504-8688  |    630-445-4033
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