What To Look For When Your AC Is Not Working

When the consistent dull hum of your air conditioner is replaced with sudden silence, it’s time to spring into action. Time is of the essence when it comes to troubleshooting (and fixing) an air conditioner that won’t turn on. As indoor temperatures rise, your home can go from cool and comfortable to hot and stuffy in a matter of minutes. But, if you stay calm and know what to check, what to fix, and when to call a professional, you can minimize the amount of time you go without reliable air conditioning. Plus, if the problem ends up being a simple one, you can save yourself the cost of a service call.

First things first: Thermostat batteries

It’s best to get the easiest troubleshooting out of the way first. Make sure your thermostat is on and that it’s set to “cool” and not “heat”. It sounds simple, but it’s a common mistake. If everything looks right, the next thing to check is the batteries. Wall thermostats typically take AA or AAA alkaline batteries, or 3V lithium batteries. You’ll usually need to change your batteries about once a year. A low battery indicator appears on the display when it’s time to replace, but this can be overlooked.

If you’re unsure of how to replace your thermostat batteries, consult your owner’s manual for instructions specifically tailored to your model. In general, to replace your thermostat batteries in a thermostat that does not have an external battery compartment, you’ll follow these steps:

  1. Pull the thermostat box off its wall mounted plate
  2. Turn the box over and use a small screwdriver to open the battery slot
  3. Discard the old batteries and replace them with new ones, then close the battery slot
  4. Put the thermostat box back onto the wall mount and slide it down until you hear it snap or click back in place.


If your thermostat has an external battery compartment, press down on the top right corner of the thermostat to reveal the compartment. Then, remove the compartment to replace the batteries before snapping it back into place.

If your thermostat springs back to life, and your air conditioner turns on with it, then the problem is solved. If not, try another one of the tips below to diagnose why your air conditioner won’t turn on.

Circuit breaker

If the problem isn’t with your thermostat, a blown fuse or tripped circuit breaker could be the culprit. Power surges, storms, and sweltering temperatures can overload the circuit, turning off the power to your air conditioner.

There are two places you may need to check to see if a circuit breaker was tripped.

Electrical service panel or fuse box

An electrical service panel serves as the switchboard operating center for all the electricity in your home. When it receives incoming power, it distributes it to each circuit that controls things like light switches, power outlets, and, most importantly in this case, your air conditioner. In an older home built before 1960, you’ll find a fuse box that serves the same purpose.

Your home’s electrical service panel may be located in the garage, a utility closet, or another generally out of the way spot. Once you’ve located it, all you need to do is open the cover and locate the tripped breaker. This is easy to spot—while the other breakers will be switched to the “on” position, a tripped one will be switched to “off”. Wait 30 minutes before turning your air conditioner back on after switching the break back on. If the breaker immediately trips again, you’ll need to work with a professional to determine the cause. The problem could be:

  • Fan motor malfunctions
  • Refrigerant leaks
  • Compressor problems
  • Frozen evaporator coil
  • Loose wiring or electrical component failure

A/C disconnect

Also known as a switch box or fuse box, an A/C disconnect can be found outside your home, close to the outdoor A/C unit. The same conditions that cause indoor circuit breakers to trip can cause the switches in the A/C disconnect to trip as well. While it’s safe to flip the switches in your home’s electrical service panel, attempting to do the same for an A/C disconnect is dangerous. You’ll need to work with an HVAC technician or an electrician if you suspect your A/C disconnect has been tripped.

Switches in and around the unit

Did you know your air conditioner actually has an on/off switch? Around the indoor unit, you’ll find several switches, including one that looks very similar to a light switch. Inside the blower door, you’ll find a small light switch that resembles the one in your refrigerator. Flick these switches to ensure that they’re set to “on” and see if that restores your air conditioner’s power. These switches can be found in units installed both on the ground and on the roof, so if getting to your outdoor unit isn’t possible for you, you can always call a professional.

Condensate overflow tray

A condensate overflow tray, or drain pan, is installed to collect water that drips off the evaporator coils during the cooling process. The condensate drain line then moves this water out of the home. You’ll find a white PVC or copper pipe located near your outdoor unit—this is where the drain line ends. Near your indoor unit, you’ll find a vertical PVC pipe with a cap on it, which acts as the access point for the condensate drain. This pipe is attached to the condensate overflow tray.

When the overflow tray is full of water, a sensor is tripped that shuts down the unit altogether to avoid water damage. The easiest way to remove the water is by using a wet/dry shop vac, available for rent or purchase at any local hardware store. Once the water is gone, your air conditioner should start back up.

In many cases, an overflow tray that’s filled with standing water is a clear sign of a clogged drain line. Drain lines are humid, damp, and ideal conditions for mold and algae, which can clog the line. There are several methods you can use to unclog the drain line. Of course, it’s also always an option to contact an HVAC or plumbing professional and have them clear the clog and clean the drain for you if you’re not comfortable doing it yourself.

Get back to cool air with Chas Roberts

If the tips in this article aren’t enough to get your air conditioner back up and running, there’s no need to worry. Our skilled HVAC technicians are trained to get to the bottom of air conditioning problems both big and small. And, with our Emergency A/C services, help is always one call away, no matter when a system breakdown strikes.