5 Reasons Why A Thermostat Clicks But AC Does Not Turn On

You know that something is wrong when the thermostat clicks but ac does not turn on but do now worry as in this post I am going to give you steps that you can follow and fix this issue.

5 reasons why thermostat clicks but AC does not turn on

There are many reasons that can explain why your thermostat clicks but ac does not turn on, but the main ones can be that the thermostat can be bad, or there is a problem is the wiring or electric component in your system, let me examine one by one and share with you the steps you can use to troubleshoot those problems.

Reason #1: You have a bad thermostat

A thermostat is the center of your HVAC system, so if there is anything wrong, this is the first place you should look. If do you want to understand more about signs of a bad thermostat please click here.

How to troubleshoot a bad thermostat?

The easiest way to figure out if you have a bad thermostat is by bypassing it, what we are going to do here is to try to turn on the AC without a thermostat.

To bypass the thermostat just take the thermostat cover off, then take the red, and yellow wire and connect the two. You do not need to turn the power off, it is only 24volts and will not harm you.

Did the system start? if yes, then replace your Thermostat. If not, then connect the wires back as they were, then proceed with the following.

Reason #2: Check your system settings

If your thermostat clicks but AC does not turn on could be due to the settings on the system, let me explain.

If the room temperature is the same as the temperature setting on your thermostat, the AC will not turn on, this is because most modern systems are designed to save energy and if the temperatures are the same there is no need to turn on the AC or heat.

The easy way to troubleshoot this is to turn is to adjust your settings and see how the system responds, also remember to change your thermostat to Heat or Cool settings according to the season you’re in.

Reason #3: You have dirty air filters

If you have dirty air filters the AC system will not turn on. The air filter is responsible for cleaning the air that goes out of the system.

When you use them for a while the air particles will start to clog in the filter and with time they will accumulate inside and prevent your system from working.

This is very easy to troubleshoot, just check them if you see dust or a change in color that is the indication of a dirty filter, you can clean them with a dry clean cloth or you can just replace them, it is recommended to replace the air filter every 90 days.

Reason #4: A bad capacitor

A capacitor is an essential part of your AC system. The capacitor looks like a drum about six inches high with three or more small connectors at the top to which electrical wires are attached. 

It acts like a battery that stores an electrical charge and releases the energy your compressor needs to start running. Without a working capacitor, your AC cannot start its fan motors and cool your home.

How to troubleshoot a bad capacitor?


The first thing I would say is that if you are not comfortable with electricity it is better to call an electrician or HVAC technician, if you feel conformable then you can continue.

The first thing you need to do is to turn off the power that goes to the outside unit. Then, open the panel and look for the capacitor.

It is swollen on the top? If the answer is yes, then it is a back capacitor, you can not fix this you will need to replace it.

If it is not swollen, you can take a multimeter ( again if you are comfortable using it) and check the voltage to the contactor on terminals L1 and L2, the voltage between these two terminals should be 240 V, is below that it is a bad capacitor.

Reason #5: A failing contactor

A contactor is basically a big switch that turns your compressor and condenser fan on and off whenever it gets the signal from your thermostat. Some people call it an electromagnetic switch.

The function of a contactor

In order for your AC system to function properly, it needs a signal from the contactor. The signal comes from the large switch that tells the AC compressor and fan to start normal operation. If the contactor is malfunctioning, damaged, or old, your AC won’t start.

How to troubleshoot a bad contactor?

Again this should be done with someone who is comfortable with electricity. In order to troubleshoot if the contactor is the problem, take an insulated screwdriver and wear heavy rubber gloves, and press down on the contacts for a second and see if it all starts up. If it does then it is a bad coil not pulling the contacts down on its own. 


We discussed 5 reasons why the thermostat clicks but AC does not turn on and the steps you can follow to figure out what is the real reason for the AC not turning on.

Again these steps involve dealing with electricity and can be dangerous if someone without training does this, my recommendation is that if you are not comfortable please can an electrician or a certified HVAC technician.



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