8 Common Reasons Why Your AC Won’t Turn On

Why Your AC Won't Turn On Blog
June 7, 2021

There are few things more frustrating than your air conditioning system not working when you need it to. Most modern air conditioners are designed to offer from 10 up to 20 years of reliable use. However, even the most reliable of air conditioners may stop cooling or suffer from problems from time to time.

One of the best ways to prevent unexpected air conditioner problems is to have regular maintenance performed on your unit.  You can hire a professional HVAC contractor like Fred F. Collis & Sons to ensure the safety and integrity of your cooling system. But what do you do if your AC won’t turn on?

Here are eight of the most common reasons why your air conditioning unit won’t work.

Common Causes of Air Conditioner Problems

Power Problems

Although this first one might sound self-explanatory, homeowners sometimes forget to check the most common cause for your air conditioners not turning on – power issues!


To fix this, check if your air conditioner is set to the “cool” setting. Lower the temperature by five degrees. If it’s still not working, check if the circuit breaker is the culprit. You can do this at your electrical box to see if any of the switches have tripped. If the issue is recurring,  give the professionals a call.

Faulty Control Board

Most air conditioners these days have something called a control board or PCB assembly. This effectively controls all the different elements of your air conditioning unit.


Check to see if the compressor or fan circuits aren’t turning on. If they aren’t, the control board is more than likely the culprit. Always check your user manual carefully before attempting to fix the problem. When in doubt, it’s always a good idea to call in the pros.

Temperature Control Issues

If the temperature in your home isn’t lowering, then the air conditioner’s temperature control unit might be to blame. Your air conditioner is usually controlled by a sensor that scans the room to monitor the temperature. If this connection from the sensor to the electrical unit is faulty, the temperature will never lower.


Check that your unit is getting power or that the fan is functioning by switching on the ‘Fan Only’ option if your air conditioner has one. Listen carefully while you adjust the temperature so you can hear if the sensor and the electrical unit are connecting with a ‘click’.

Thermostat Is Defective

If your air conditioner isn’t turning on, the thermostat could be defective. Without a working thermostat, your air conditioner won’t be able to tell when it should turn on and off.


Check to make sure the thermostat is switched on. If not, it could’ve been turned off. This is easy to fix by simply switching it back on. If this isn’t the issue, try replacing the batteries to see if anything changes. If all else fails, it might be time to call in the professionals for advice and/or for them to install a brand-new thermostat for you to cool things down.

Clogged Drain Line

Just like the heating oil line, the condensate drain line can get clogged, causing damage. As they operate, air conditioning units create condensation, which goes through a drain line. Naturally, if this line is clogged, your air conditioner won’t turn on, as a safety switch will trip to prevent serious damage or hazards.


Unclog the line. You could potentially use a shop vac or some other means of suction to open it back up again. Alternatively, if your air conditioning unit has a condensate drain pump to perform this function, it could be faulty and what’s causing the safety switch to trip.

Air Filter is Clogged

An old or clogged filter can cause your air conditioner to turn off or perhaps even freeze up.


Ensure that you’re regularly cleaning or replacing the air filter in your air conditioning unit.

Drain Pan is Flooded

If the pan under your indoor air conditioning unit is full of water, your air conditioner won’t turn on for safety reasons.


Empty it out and the issue should be resolved. If not, some other element could be causing the issue.

Dirty Air Conditioner

If your air conditioner isn’t turning on, the problem could be something as simple as the fact that it’s dirty. If your evaporator coils or condenser lines are dirty, they may refuse to switch on.


Schedule a regular air conditioner service to ensure everything is and remains in tip-top shape.

We know this all can be overwhelming – that’s why we are here to help! When you need air conditioning products and services, trust Fred F. Collis & Sons to take care of you. We provide heating, cooling and air quality solutions. We also deliver fuel oil for your oil furnaces. Call us today at (315) 737-4143 or complete our online form to experience the Collis difference.

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