What to Do When Thermostat Clicks but AC Does Not Turn On? Troubleshooting Guide [2023]

Whether the sun is raging with extreme heat or the snow is showering the earth with its cold, white flakes, we always rely on the thermostat to keep a comfortable environment inside our home.

So it can be a real bummer if you get back home from outside and find out the AC system is not working.

As you proceed to check the thermostat, you realize that the thermostat clicks but AC does not turn on.

And now you’re scared as installing a new HVAC system can break your bank account.

But let me comfort you by informing you that there can be several technical reasons why your thermostat clicks but the AC isn’t turning on.

In this blog post, we will discuss the 7 most common reasons for your AC not turning on and how to solve them.

Thermostat Clicks but AC Does Not Turn On – 7 Possible Reasons & Their Solutions

Let’s delve into the reasons and their solutions for your AC not turning on even if the thermostat clicks.

Reason 1: Dirty Air Filter

Air filters are usually installed in the return air duct or at the air handler/furnace unit. They are made of fibrous materials that are designed to trap pollen, dust, and other air particles.

An air filter’s main function is to improve indoor air quality. It also protects the AC system by preventing dust and debris from going in.

When an air filter becomes dirty or clogged, it starts to block the airflow to the AC unit. This reduced airflow results in freezing up the evaporator coil, making your AC unable to produce cool or hot air.

If not taken care of for long, this can trigger the AC’s safety mechanism to prevent any damage.

As a result, the thermostat may click, but the AC won’t turn on because the safety mechanism will stop it to avoid further complications.


To solve this issue, you should clean your air filters every month and replace them every 2-3 months.

Consider investing in a higher-quality air filter that can screen out even smaller particulates.

Reason 2: Wrong Thermostat Settings

If you can’t find any abnormalities in the AC’s air filter, It’s time to check the most basic issue there can be, the thermostat settings.

The thermostat is a control device that communicates between you and the HVAC system. Setting a specific temperature on it sends a signal to the AC to turn it on or off to maintain that specific temperature in the room.

Like if you are trying to cool down the temperature inside your house, you will set it to a lower temperature. Alternatively, you will set it to a higher temperature if you are trying to warm up.

If you do not maintain the right settings, the thermostat will click, but the AC won’t turn on.

It means if you are trying to cool down the room, but you have set a temperature that is higher than the room temperature, the AC won’t turn on.

Similarly, the AC won’t turn on if the thermostat temperature is set to the same temperature as the room.


First, check if the thermostat is ‘On’ and is set to ‘Cool,’ Warm,’ or ‘Auto’ mode. Then check the fan to make sure it is in ‘On’ and ‘Auto’ mode.

Once you are sure the thermostat modes are set perfectly, start checking the temperature settings.

Make sure the thermostat temperature isn’t set to the exact room temperature. Set the thermostat to a higher temperature for warm air and a lower temperature for cool air.

Reason 3: Wrong AC Settings

If your thermostat is set to the right settings and it’s still not turning on the AC, you should check the AC settings.

It may sound silly, but we often forget to turn on our AC or plug in the power chord after returning home.

If this is the case, then the thermostat will click but the AC won’t turn on.


Check the circuit breaker and fuses in your home’s electrical panel if the AC isn’t turning on due to no power.

You should also check your AC system’s wiring for any damaged wires.

Reset the circuit breaker and replace any burnt fuses, then ensure the AC unit is properly plugged into an electrical outlet.

Reason 4: Faulty Capacitor

Capacitors work as batteries for your HVAC system. You can expect two single capacitors or one dual capacitor in your AC unit.

Capacitors store an electrical charge, which is used to start the compressor when the thermostat signals the AC for cool or hot air.

If the capacitor is damaged, it won’t be able to send the necessary electrical charge to the compressor to start its functions.

And if the compressor doesn’t start, the AC won’t turn on either, but you will still hear the thermostat clicking.


Listen closely for any buzzing noise coming out of the AC. If you hear one after the thermostat clicks, it means the compressor is trying to start without the required electrical charge.

This proves that you have a faulty capacitor at hand. But since it’s an electrical component, it’s always best to hire a professional technician to replace the capacitor for you.

Reason 5: Faulty Relay Circuit

The clicking sound of a thermostat is basically the relay circuit being completed. A relay circuit controls the electricity flow within the AC system.

It allows the thermostat to send signals to the compressor and the blower motors to start them.

A single break in the whole relay circuit can stop the electrical signal from passing on and triggering the AC.

As a result, the thermostat will click, but the AC won’t respond because of not getting the signal.


Perform a continuity test using a multimeter to confirm if the relay circuit is faulty. If there’s no continuity when the relay is clicked, it strongly indicates that the relay needs replacement.

You should also examine the relay connection for any damaged or loose wiring and repair it if you find any.

If there is no damage to the connections, try resetting the thermostat breaker in your home’s breaker panel.

Turn the breaker off for 1-2 minutes, then flip it on again. If the thermostat is still clicking but the AC isn’t turning on, it is a sign that your thermostat has a faulty relay circuit.

Another way to check if your relay circuit is faulty is to listen to the thermostat once you turn it on. If the clicking noise is louder than usual, there’s a high chance that its relay circuit is malfunctioning.

In any such cases, you should consult an electrician to help you repair or replace the faulty relay circuit.

Reason 6: Faulty Control Board

Apart from faulty capacitors and relay circuits, a faulty control board can also be the reason for your AC not turning on.

The control board is the central control unit of the AC system, which receives signals from the thermostat and sends them to the different components like the capacitor, compressor, and fans to trigger the AC to turn on.

If your control board malfunctions, it won’t be able to convey the electrical signal from the thermostat to the AC, compromising the timing and operation of the AC system components.

As a result, when you turn the thermostat on, you will hear the clicking but the AC won’t turn on.


If your AC behaves erratically, like failing to maintain the temperature or turning off unexpectedly, it’s a sign that you have a faulty control board.

If your AC has turned off by itself while operating, and you are hearing a clicking noise coming out of your AC system, it’s high time that you bring in an HVAC expert to replace the control board.

The latest control boards come with a reset button, so you can also try resetting the control board before you proceed with replacing it.

Reason 7: Faulty Contactor

If all the issues mentioned above are checked out, it’s time to check the contactor. It’s an electrical switch that is generally installed in the outdoor unit of the AC system.

A contactor is responsible for engaging and disengaging the electrical connections to the compressor and the condenser fan motors.

A faulty contactor will disrupt the electrical signals between the thermostat and the AC system components.

This will cause the thermostat to click without the AC responding because although the thermostat is sending the necessary signals, the AC system isn’t receiving them.


If your thermostat clicks but the AC is making unusually loud noises without getting turned on, a faulty contactor is often the main reason for it.

A contactor has sensitive electrical connections; if damaged, they require a complete replacement.

Contact your local technician so they can come and take care of the job for you.

Bottom Line

Air conditioning is one of the most necessary appliances for our daily life, and with proper maintenance, it can serve our home year after year.

But like any electrical appliance, AC systems can also malfunction occasionally, and the reasons have been discussed thoroughly.

If you notice any of the issues mentioned in this article, you should immediately address them and seek professional help before the problem gets more serious and damages your whole AC system.


Is thermostat working if it clicks?

Yes. There are two mechanical relays inside the HVAC system that move when the internal circuit of the thermostat sends signals to the AC system to turn on or off.

These mechanical relays produce a clicking sound, which indicates that the thermostat is working.

Can thermostat damage AC?

If your thermostat has faulty wiring, it can cause the AC fan to spin without stopping. It poses a heavy strain on the fan motor and ultimately damages the AC.

When should thermostat click?

The thermostat clicks one time when it starts the heating or cooling cycle, then clicks once again once it signals the end of one cycle.