Thermostat clicks but A/C does not turn on (What Should You Do)

We’ve all been there. You go to turn on your A/C on a hot day and it clicks but doesn’t turn on. Our minds wander to the worst possible situation: having to call someone to come out and tell you it’s going to be quite expensive to fix. Fortunately, you can do a few things before you have to come to that point.

A thermostat is the control system for your A/C. It turns it on and off, along with controlling the temperature of your home. When your thermostat clicks but the A/C does not turn on you’ll want to start checking, troubleshooting, or cleaning parts of the unit before having to replace anything.

Know How an A/C System Works

Before you get started on trying to fix the problem you should have an understanding of how an A/C system works. This will ensure that you won’t accidentally cause harm to it, making your A/C problem even bigger.

Many believe that an A/C creates cold air but that is not the case. An A/C works by pulling in air from the outside and running it through a filter and an evaporator coil. The evaporator coil is filled with a refrigerant. This refrigerant is a chemical that absorbs warm air and leaves cold air to run through it. The cold air is then pushed through a filter and into your vent system. The air runs through your vent system and blows into the house. 

A/C System

It may seem like a complicated system but when you take a closer look at the system it becomes a lot easier to understand.

If your A/C is not turning on when the thermostat clicks there may be a problem with any of those systems or even the thermostat itself. However, the fix may be as simple as some troubleshooting. 

Do a Simple Check

The first thing you should do when your thermostat clicks but the A/C does not turn on is to do some simple maintenance checks. Checking out your A/C system may save you a lot of time and money. A lot of times, the reason why an A/C system doesn’t turn on is that the system needs to be reset or certain parts need to be cleaned. 

Check your thermostat and its settings 

Check that the temperature of your A/C on the thermostat is lower than the temperature that is displayed by the thermostat. Check to make sure the thermostat is set to cool instead of heat. Then check to see if the fan is on auto or on. 

Check your thermostat and its settings 

If your thermostat is at a proper temperature, it’s set to cool, and the fan is set to on then you may need to check if your thermostat has gone bad which we will go over in a later section.

Check your indoor/outdoor unit 

If you realize the clicking sound is inside when you turn on your A/C but it is not coming from the thermostat then there is an issue with your indoor unit. 

The clicking that may be coming from your indoor unit would be coming from the control board. This board sends the signals from the thermostat to the unit.

Check your indoor/outdoor unit 

In case you are not hearing any clicking from the thermostat or control board then check your outdoor unit. The two issues that could be coming from the outdoor unit are a failed contractor or failed capacitor. 

Check the relay

The relay is what opens or closes an A/C when you turn either turn the thermostat on or off. To check if it is the relay listen to see if the clicking noise is unusually loud or if the clicking lasts for a couple of seconds. If so, the issue may be the relay. 

Check the relay

Some thermostats allow you to check the relay on your own by seeing if the LED of the relay flashes on. If you turn on the A/C and the LED does not flash on then you may have found the reason why your A/C will not turn on.

Ensure the capacitor isn’t defective

The capacitor is part of the outdoor unit and is what powers up the A/C compressor. A capacitor is part of older A/C units so if you do have an older A/C unit this could be the issue. Over time the capacitor loses charge.

Check your capacitor if working

If the capacitor is the issue you will hear a clicking noise and a low buzzing sound. You can also go to your outdoor unit and see if there is any discharge on the unit or bulging anywhere on it.

Check your furnace to make sure that’s not the problem

To check to see if your furnace is not the problem you will need to check the air filters. Dust and other residues may build up on the air filters. This means that there is not enough space for the air to properly flow through the filters. 

This does not mean your furnace is the issue but the air filter is the issue which is a lot less costly to fix. It is unlikely that your furnace would be the main problem. It is just the furnace has been disrupted by the clogged filters.

Fixing the Problem

Now that you have gone through a checklist of what may be the issues you’ll want to find the best solutions. If the issue isn’t as simple as changing the settings on the thermostat, you’ll want to hire a professional. Although it is possible to fix some of the issues yourself, hire a professional to come out and do the work for you so you don’t damage your A/C unit.

Replace the Control Board 

The control board should be by the furnace system. To replace the control board you’ll want to start by disconnecting the power cord so there is no possibility of being shocked. The furnace should have a lower panel where the control board is. You’ll want to unscrew or open that.

Change the Control Board if needed

Once you see the control board you’ll want to unscrew the screws holding in the wires so that you can take those wires out. Once the wires are disconnected you’ll want to unscrew the control board from the furnace.

After the control board is out you should add in the new one to reconnect it to all of the proper wires and screw it back into the furnace.

Replace the Air Filters 

To replace the air filter you should turn the power of the system for safety. Then you’ll want to open the vent up revealing the old air filter and take that out. Put in the new air filter. Make sure the air filter’s arrows are pointing toward the A/C unit. Close the vent back up and you’ve successfully installed a new air filter.

Change the Air Filters if needed

Change Your Thermostat 

In order to change your thermostat you’ll want to go out and make sure you buy the correct one. When you are ready to change it go ahead and turn off the power to the system. After that, you’ll want to unscrew the old thermostat and disconnect any wires until it is completely separated from the system.

You should label the wires so that you know which ones to connect the new thermostat too. Then go ahead and reconnect all the wires to the new thermostat and screw it back into the wall. It should turn after you turn the power r to the system back on.

Change the defective capacitor

Changing a defective capacitor is no easy job. This is because the system is a lot more complicated and potentially dangerous. If you realize that the capacitor is bloated or there is discage coming from it you are best off calling a professional to change it for you.

If the capacitor is defective replace it

If you plan to give yourself a challenge and want to put in the time and effort to change a capacitor it would be best to watch multiple videos on how to change it along with getting familiar with your A/C unit to ensure you do not harm yourself or cause any damage to your new capacitor.

Replace the contractor

The contractor of an A/C controls the flow of electricity. The contractor is connected to the condenser and is a part of the control panel. When you open up the control panel you will see a vertical black rectangular box. There will be colorful wires connected to it.

You should take a picture of the wiring so you will know where to reconnect the wires when you put in the new contractor. After you remove the screws and wires of the only contractor you just need to reconnect the new one to look like the picture you took.

What Do I Need to Fix?


  • Adjustable wrench or multiple wrenches
  • Screwdriver
  • Multimeter
  • Pliers
  • Nut driver
  • Socket set


  • Control board
  • Air filter
  • Thermostat
  • Contractor


There are a number of issues that you can check when your thermostat clicks but the A/C doesn’t turn on. Some of those issues may be small and some may be a sign to call a professional for help. After checking those issues determining what you want to do is the next step. 

Replacing parts of an A/C unit may be less costly but could result in causing the A/C unit more damage. Calling an expert on A/C units may be the best option to get your A/C unit up and running again.

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