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Why Won’t My Central AC Turn On?

March 29, 2023

We’ve all been there. It’s h-o-t, and the AC blower fan won’t start up, the thermostat completely ignores you, and nothing works! If your AC won’t turn on, it’s a problem you need resolved quickly to survive Arizona’s heat.

Many central air conditioners fail to turn for these reasons:

  • Thermostat issues
  • A tripped circuit breaker
  • A dirty air filter
  • A clogged condensate line

Your Patrick Riley | Isley's experts have seen it all here in Phoenix, but sometimes it doesn’t take a professional to find out what might be wrong with your system. We’ll walk you through a few things you can try to get your AC up and running before you have to call the professionals.

AC Won’t Turn On: What to Do

Step 1: Check Your Thermostat

If you have a hybrid heating and cooling system, did you make sure the thermostat was set to “COOL” and not “HEAT”? If the thermostat is set to COOL, try turning the temperature at least five degrees below the room temperature.

If the thermostat isn’t working at all, you may have to replace the batteries. If the thermostat still does not work after changing the batteries, there may be a wiring issue that you’ll need to have a Patrick Riley | Isley's professional solve.

Head over to Step 2 if your thermostat isn’t the issue.

Step 2: Check Your AC Circuit Breaker

Find your electric panel and check the AC’s circuit breaker. It should look like this:

If the air conditioner’s breaker is tripped, then you’ve easily solved the mystery behind why your AC unit won’t turn on.

Here's How to Reset the Circuit Breaker:

  • Power your air conditioner down from the thermostat’s control panel.
  • Switch the breaker to the “OFF” position.
  • Switch the breaker to the “ON” position.
  • Turn your thermostat on and ensure the temperature setting is five degrees below the room temperature.

Your AC will (hopefully) turn on at this point.

If the breaker doesn’t “click” when you flip it or if the breaker trips immediately after you turn the AC back on, you need to have an expert look at your AC. The breaker trips to prevent a more serious problem from happening with your AC, so you’ll need a professional to address this before your unit can run normally again.

What Causes the AC Circuit Breaker to Trip?

Many different things will cause an AC circuit breaker to trip. The worst-case scenario would be a short circuit somewhere in the wiring. Or it could be that the breaker itself has gone bad. Replacing circuit breakers is relatively inexpensive, but you’ll need a professional to help you with this.

Sometimes the circuit breaker trips because the AC is drawing too much electrical current, causing it to overheat.

What Would Cause the AC to Overheat?

  • The outdoor unit is dirty.
  • The outdoor unit is covered by a surrounding bush.
  • The air filter is dirty. (We cover this in detail in the next section.)

Why a Clean and Clear Outdoor Unit is Important

In order for your AC system to cool your home, all that heat has to go somewhere. An indoor unit absorbs heat from your indoor air and then “dumps” that heat outside via the outdoor unit.


If the outdoor unit is dirty or covered by a bush, it makes sense that it would struggle to release that heat, causing your unit to overheat, the breaker to trip, and the AC unit not to turn on.

So, after you flip the breaker back to “ON,” check the outside unit and make sure that it’s clean and clear of any shrubbery.

A dirty air filter could cause your unit’s breaker to trip or, in some cases, cause your unit to stop running altogether. So, whether you successfully reset your breaker or the breaker wasn’t the issue, your next step is to check your air filter.

Step 3: Check Your Air Filter

Changing the air filter is a necessary maintenance task that helps keep your air conditioner running and your family breathing fresh clean air. Most air filters last for around three months before they get full of dust and need to be replaced.

Why a Dirty Filter Can Shut Down an Air Conditioner

A dirty air filter reduces airflow into the AC’s return vent. This reduced airflow can cause several issues:

  • Outdoor unit overheats — Since the AC can’t circulate enough air, the AC struggles to cool your home, meaning it runs constantly. This constant running can cause the outdoor unit to overheat and trip the breaker.
  • Indoor unit freezes — Your AC’s indoor unit has a cold copper coil (evaporator coil) that cools your indoor air. However, when airflow is reduced over this coil, it gets too cold, freezes, and eventually trips a safety switch, which shuts down the AC.

If you have not changed the filter before, it’s rather simple:

1. Turn off your AC at the thermostat.

2. Find the return vent in your home.

This return vent is in a stairway. Your vent may be elsewhere.

3. Change the filter if it’s dirty.

4. Reset the AC thermostat.

5. Turn on the AC at the thermostat.

If the filter isn’t dirty, go to Step 4 below.

Step 4: Check for a Clogged Condensate Line

Your AC unit not only cools your home, it dehumidifies it, too. As your AC dehumidifies the air, water gathers on the cold copper coils and drops down into a condensate line, which makes its way outside the home.

Unfortunately, over time, this condensate line can get clogged with dust, mold, and other substances. When this happens, water backs up into the AC and trips a safety switch that shuts down the AC.

Here's How to Clean the Condensate Line:

  • Get a shop vac and some duct tape.
  • Take both items to the outdoor condensate line. It may be near your AC outdoor unit.
  • Connect the vacuum to the condensate pipe and wrap the connection around using the duct tape.
  • Turn on the vacuum and let it run for 3–5 minutes.
  • Turn off the vacuum and check for any gunk in the vacuum.
  • Repeat if necessary.

Following these steps may fix the problem, allowing the AC to turn back on. If your AC won’t turn on after flipping the breaker, call 602-286-0027.

Need Help with Your AC System?

If you’ve exhausted all of your DIY options, you’ll need a professional to come and fix it. Schedule a repair with Patrick Riley | Isley's today! We know our way around all kinds of cooling machines and will determine why your AC won’t turn on. Homeowners in Phoenix, Mesa, Chandler, and surrounding Arizona cities trust the quality of our work, whether it’s for furnace, HVAC, or plumbing repairs.

Why Choose Patrick Riley | Isley's

Patrick Riley | Isley's has friendly technicians all across Maricopa County to ensure we can get your HVAC repair done quickly and painlessly and to your complete satisfaction. Sign up for a flexible payment plan, check our Coupons page for this month’s savings opportunities, or consider a VIP maintenance plan for scheduled maintenance and exclusive discounts. We help alleviate the most anticipated problems that come with repairing the inside of an AC unit.

Originally published: October 3, 2016

Written by: Patrick Riley | Isley's

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By Ty Lindsay

Ty Lindsay is the Director of Field Operations at Patrick Riley | Isley’s and a 15-year veteran of the plumbing and HVAC trades. In 2010, Ty earned his Journeyman’s plumbing license. He became a Master Plumber five years later and earned his Journeyman HVAC technician’s license that same year. Ty’s breadth of knowledge in plumbing and HVAC includes both residential and commercial work. He’s been a loyal member of the Patrick Riley | Isley’s team since 2016.