How to fix a thermostat in AC?

Author: Mrs. Briana Krajcik MD  |  Last update: Wednesday, July 30, 2025

DIY Thermostat Repair Guide
  1. Check the Circuit Breaker or Thermostat Setting. A lack of heating or cooling can be due to a tripped circuit breaker. ...
  2. Turn the Temperature Up or Down. ...
  3. Replace the Battery. ...
  4. Fix Loose or Disconnected Wires. ...
  5. Clean the Thermostat. ...
  6. Level the Unit. ...
  7. Test the Terminals. ...
  8. Perform a Transformer Test.

How to fix air conditioner thermostat?

DIY Thermostat Fixes
  1. Step 1: Change Batteries. ...
  2. Step 2: Check Circuit Breaker.
  3. Step 3: Check Thermostat Programming. ...
  4. Step 4: Ensure The Furnace Switch Is Providing Power To The HVAC System. ...
  5. Step 5: Facilitate Air Flow.

Can I replace AC thermostat myself?

No! If you have the tools required, you should be able to replace a thermostat yourself. There are instructions with the new thermostat that will tell you exactly how to do it but if you don't feel comfortable doing it yourself, you can hire a local handyman, HVAC tech or electrician.

How do I tell if my AC thermostat is bad?

Signs of Thermostat Failure
  1. The Heater or AC Unit Won't Start. Wiring can shift and come loose over time. ...
  2. Air Conditioner/Furnace Run Continuously. ...
  3. The Thermostat Is Unresponsive. ...
  4. Different Temperatures Throughout the Home. ...
  5. The Interface Won't Respond.

How much does it cost to replace an AC thermostat?

The cost to install a thermostat is $182 on average, but you could pay between $113 and $264. Thermostats play an important role in our daily lives, cooling us down during the sweltering summer heat and keeping us warm and cozy during winter. While the average cost to install a thermostat is $182, pricing can vary.

How to Reset an AC Thermostat

Will AC run if thermostat is bad?

So, can a bad thermostat cause your AC not to cool? Absolutely. While it may seem like a small part of your HVAC system, the thermostat plays a crucial role in ensuring your home stays cool and comfortable.

How do I know if I need a new AC thermostat?

A malfunctioning thermostat has a harder time maintaining a setting, and may quickly shift temperature settings with no warning. If your central air has a difficult time maintaining the set temperature, even after lowering a setting for a test trial, it could be the thermostat.

How do I reset the thermostat on my AC?

Switch the thermostat to the off position. Locate the breaker that powers your HVAC system and turn it off. Wait 30 seconds and turn the breaker back on. Turn your thermostat back on and confirm it has reset properly.

Is it hard to replace a thermostat?

Your thermostat instruction manual can tell you exactly how to change a thermostat. Installing the thermostat yourself is an easy task that will typically take about an hour from start to finish.

Why is my AC not turning on?

There are a number of reasons why your AC unit may stop working unexpectedly, including electrical problems, blockages, thermostat issues, and more. Troubleshooting includes checking your circuit breakers, thermostat settings, and replacing your air filters.

Can an AC work without a thermostat?

Your thermostat reads the temperature of the room, then sends an on or off signal to the air conditioner. The AC itself isn't detecting the temperature in your home, so it has to rely on the thermostat.

Can I just buy a new thermostat?

You can typically just replace the outdated thermostat with a new thermostat – assuming the latter is compatible with your HVAC system. There are a few things you should know, however, when upgrading your thermostat.

Will a new thermostat fix my AC?

Replacing your thermostat when you install a new AC system is a great idea. The connection between the thermostat and AC is important to the function of the system. Problems with the thermostat can cause the AC to run more often than it should or not as often as it should.

Who do I call if my thermostat isn't working?

If your wires are connected but your thermostat still isn't working properly, that means it's time to hire a professional. They'll open the thermostat and test the wires individually to see which one is faulty. Since messing with wires is dangerous, you'll want to contact a certified HVAC technician.

Do I need an electrician to replace a thermostat?

Yes, many smart thermostats are designed for DIY installation, and manufacturers typically provide step-by-step guides and videos. However, if your HVAC system is older or lacks proper wiring (like a C-wire), the installation might become more complex, and you may need professional help.

Why is my AC set to 72 but reads 78?

Clean the Thermostat

Sometimes, when the room temperature doesn't match the thermostat setting, the problem could be dirt buildup on its interior parts. A dirt coating around the inner components may create excess heat and cause the thermostat to give the wrong readings.

How much is a new AC thermostat?

The average cost of a new thermostat, including installation, ranges in price from $50 to $500 or more based on several factors including the type of thermostat, labor costs, the complexity of the installation, and more.

How to tell if a thermostat is bad?

A bad thermostat can be detected when your AC or furnace is not turning on, your HVAC systems are not turning off, the thermostat not responding, your HVAC system is short-cycling, the room temperature not matching the temperature displayed on the thermostat, and the programmed setting resetting themselves.

Can I install a new thermostat myself?

In most cases, installing a new thermostat is a relatively simple do-it-yourself project that can result in improved comfort and convenience and one that can help you save energy.

Will AC stop working if thermostat is bad?

The heating, ventilation, and air conditioning (HVAC) system in your home is controlled by your thermostat. If your thermostat isn't working, your furnace, whole-house fan, and AC unit are probably not functioning correctly, either.

Why is AC not blowing cold air?

First, check your filters and coils for dirt and debris that may be impeding airflow. Once you've cleaned the filters and coils, run the air conditioner with just the fan so that the ice accumulation can melt off. If the AC still doesn't blow cold air, it could be that refrigerant levels are too low.

Where is the AC reset button?

In AC systems, the air conditioner reset button is on the outside unit's lower edge, typically close to the ground. Some models have the reset button located behind the service panel, which may require tools to remove. Reset buttons are usually red or yellow with a clear “reset” label.

Will resetting my thermostat fix my AC?

Any time you are having an issue with heating and cooling units, such as after a sudden power failure or after your children have had 'control' of the system while you've been away, resetting the thermostat should be the first thing you try when attempting to rectify HVAC system issues.

How do I test my thermostat?

Methods for Testing Your Thermostat
  1. Just Turn it On and Let it Work. One way to test your thermostat is to simply turn it on and see if it cools the room down. ...
  2. Get an Indoor Thermometer. Another way to test your thermostat is to use a thermometer. ...
  3. Use a Multimeter. ...
  4. What to Do if You Notice an Issue.

Who can install a new thermostat?

HVAC repair pros are a good option if you're looking for someone to replace a thermostat. In fact, you may find that many thermostat installers work with an HVAC company. Plus, by hiring an HVAC expert to replace your thermostat, you can also book an HVAC inspection at the same time.

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