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Why Is My Central Air Conditioner Blowing Hot Air? [FAQ]

“Why the HECK is my air conditioner blowing warm/hot air?” I don’t think anyone could ask that question in a non-ticked off tone, considering Arizona’s “wonderful” summer weather and all.

Anyway, down to brass tacks. 

Your air conditioner blowing hot air out the vents could be caused by a variety of problems. 

Here’s an overview of a few common Issues:

  • Thermostat is on the wrong fan setting
  • Refrigerant leak
  • Dirty air filter
  • Dirty outside AC unit
  • Tripped breaker

Let’s go into each of these in more detail.

1) THERMOSTAT IS ON THE WRONG FAN SETTING

Your thermostat’s fan setting controls (you guessed it) the fan in the air handler, which is your AC’s inside unit.

Check the fan setting now.  What is it set on?? 

If it’s set to “On” you may have found the problem. “On” means the fan runs 24/7—even when the air isn’t being cooled. That’s why the air may feel warm or hot sometimes.

Solution: Turn your fan setting to “Auto,” making the fan automatically turn on only when you need cooling.  

2) REFRIGERANT LEAK

Refrigerant is a heat transfer liquid; it’s responsible for absorbing the heat from your air. So if you’re low on refrigerant, your AC can’t cool your air well—especially on hot days. 

The only way refrigerant gets low is if you have a leak (refrigerant isn’t used up like gas).

Signs you have a refrigerant leak:

  • Frozen refrigerant line (check your outside unit; you’ll quickly see it if it’s frozen)
  • AC blows hot air during the day, but cold air at night
  • You hear a hissing or bubbling noise near AC (this means the leak is significant)

Solution: If you see these signs, you need to schedule an air conditioner repair. The technician will need to find the leak, repair it (if possible), and add refrigerant.  

3) DIRTY AIR FILTER

When you leave your air filter in your AC system too long, it gets full of dirt (especially during the monsoon season) and becomes worse than useless—it can do real damage to your AC.

A dirty air filter blocks return airflow to your air conditioner, preventing your AC from cooling normally.

Solution: Check the filter at least once a month and change that sucker ASAP if it’s dirty. 

4) DIRTY OUTSIDE AC UNIT

Long story short: The outside unit’s job is to disperse heat from the refrigerant so it can absorb more heat from your air.

Anyway, if the outside unit gets too dirty, it has trouble dispersing the heat, and thus your AC struggles to cool your air.

Learn more in our article Dirty AC Condenser Coils: Why You Need Them Cleaned in Phoenix.

Solution 1: Clean the outside unit at LEAST once a year using a garden hose on a gentle setting. DON’T go full blast or you’ll bend the condenser coil fins and hinder airflow.

Solution 2: If you want to get your outside unit properly cleaned (and prevent AC breakdowns,) then you need air conditioner maintenance.

It’s just like getting maintenance for your car (except instead of every 3,000-6,000 miles, it’s once a year).

5) TRIPPED BREAKER 

Your air conditioning unit has two breakers: one for the outside unit, another for the inside.

If the outside unit’s breaker trips, then the inside unit will continue to blow air in your home, it just won’t be cooled off.

Solution: Check your breaker box and see if the inside unit’s breaker is tripped if so, reset the circuit breaker. If the breaker trips again, DON’T reset it. Doing so could damage your AC.

Learn why in our article “Why is My Air Conditioner Tripping the Circuit Breaker?”

You’ll need to schedule an air conditioner repair to solve this problem.   

JUST A FEW PROBLEMS OF MANY

The above 5 issues are just a handful of problems that could cause your A/C to blow hot air. To find the true problem, you need a professional A/C technician to check your system.

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