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Central AC Won't Turn On? A Phoenix Tech Explains Why

September 23, 2016

If your central air conditioner won’t turn on, there could be a cornucopia of issues causing it. (Trust us, we’ve seen it all).

However, you don’t need a professional AC technician to solve all the problems you might be facing.

Many central air conditioners refuse to turn on because of:

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

So, before contacting an AC repair tech for help, do these 4 things:

Step 1) Check the thermostat

Simple digital thermostat

OK, bear with us here. Did you make sure the thermostat was set to “COOL” and not “HEAT”? Even if it is set to COOL, try turning the temperature at least 5 degrees below the room temperature.

If the thermostat isn’t working at all then you may have to change the batteries. If the thermostat still does not work after changing the batteries, there may be a wiring issue that a professional needs to solve.

If the thermostat does not seem to be the issue, then...

If the thermostat isn’t the issue, then...

Step 2) Check the AC circuit breaker

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

Circuit breaker at an Arizona home

If the air conditioner’s breaker is tripped, then that explains why the AC won’t turn on.

Do this:

  • Turn your air conditioner off at the thermostat
  • Turn the breaker to the “OFF” position
  • Turn the breaker to the “ON” position
  • Turn your thermostat on at the thermostat and ensure the temperature setting is 5 degree below the room temperature

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

If the breaker does not “click” when you flip it or if the breaker trips immediately after you turn the AC back on, you have a bigger problem and should contact a technician.

What causes the AC’s breaker to trip?

Tons of things. Worst case scenario is that you have a short circuit somewhere in the wiring. Or it could be that the breaker itself has gone bad. Which isn’t a big deal, as replacing circuit breakers is relatively inexpensive.

Bad circuit breaker

But, sometimes, the circuit breaker trips because the AC is pulling too much electrical current because it’s overheating.

What would cause the AC to overheat? Common causes include:

  • 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)

Dirty outdoor AC unit in Mesa, AZ

This bush is getting too close for comfort to this AC unit

Let’s talk about why a clean and clear outdoor unit is so important.

You see, in order for your AC system to cool your home, an indoor unit has to absorb heat from your indoor air and then “dump” that heat outside via the outdoor unit.

However, if the outdoor unit is dirty or smothered by a bush, it struggles to release that heat, causing the unit to overheat and trip the breaker.


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.

You’ll also want to check one more thing: the air filter.

Step 3) Check air filter

Do this:

1. Turn off your AC at the thermostat.
2. Find the return vent in your home.

Return vent in the stairway. Your vent may be elsewhere.

3. Change the filter if it’s dirty

Left: Clean filter, Right: Dirty filter

4. Turn on the AC at the thermostat.

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

Why a dirty filter can shut down an air conditioner

A dirty air filter reduces airflow into the the air conditioner 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.

Step 4) Check for a clogged condensate line

Your air conditioner 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 exits outdoors.

Condensate line exit

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

Do this:

  • Get a shop vac and some duct tape.
  • Take both items out to the outdoor condensate line. It may be near your AC outdoor unit.
  • Connect the vacuum to the condensate pipe and ensure you have tight seal 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.

Doing the above may fix the problem, allowing the AC to turn back on.

Need an AC repair in AZ? Call us!

If you’ve exhausted all your DIY options, you’ll need a professional to find and fix the root problem. If you live in the Phoenix metro area in AZ, schedule an AC repair with Patrick Riley Services.

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