Why is my outside AC unit running when the thermostat is off?

Author: Denis Baumbach PhD  |  Last update: Friday, October 10, 2025

The Short Answer Is: When your air conditioning system keeps running and never seems to shut off, the problem could be linked to a number of malfunctioning components – frozen evaporator coils, a clogged air filter, a bad electrical relay switch that needs to be replaced, the fan blowing constantly, dirty condenser ...

Why is my outside AC unit running but the thermostat is off?

If your air conditioner keeps running when it's turned off this could be a sign of shorted thermostat wiring. A continuously running air conditioner could also be triggered based on the settings selected for the unit.

Why is my thermostat off but still running?

If your thermostat is off but heat is still on, you are probably experiencing some kind of "short" or connection issue. Most often with this problem is that a wire is touching something it should not be touching. Another possibility is that the gas valve is stuck open. This is rare, but it can happen. If.

Why is my outside AC unit not shutting off?

Malfunctions affecting different system components can prevent the conditioner unit from shutting down as expected, such as a clogged air filter, a frozen evaporator coil, a faulty electrical relay switch, a dirty condenser coil, a constantly blowing fan, a bad thermostat, low refrigerant, and other HVAC system repair ...

Why won t my AC turn off even when the thermostat is off?

Key Takeaways. If your AC won't turn off, it could be due to thermostat malfunctions, electrical component issues, dirty or clogged components, or an incorrectly sized system, which can increase energy bills and reduce system efficiency.

A/C Condensing Unit Runs Constantly T-stat is OFF

Why does my AC keep running after temperature is reached?

When the coils freeze, they can't efficiently transfer heat, causing your air conditioner to run continuously. This can be due to low refrigerant levels, poor circulation, dirty coils, power issues at the outdoor unit, setting the AC unit temperature too low at night, or power issues at the condenser.

Why is air blowing when the thermostat is off?

Then, when the air conditioning is off, the contactor prevents electricity from entering your AC unit. Over time, your contactor can collect dirt, attract insects, or get stuck in a certain position. As a result, it may stop working properly—which can force air out of your vents even when your AC is off.

Why is my AC unit running when off?

This can happen because your system is set to ON instead of AUTO, and a simple switch on the thermostat can do the trick. Another reason this can happen is because there is a delay between turning off the air conditioner unit and the actual system shutting down.

How do I reset my outside AC unit?

It's a small, red button usually located on or around the unit. The button should have a clear 'reset' label. Once you find the button, press it for around three seconds and observe the AC. Check whether the AC kicks on immediately and if it doesn't, press the button again for another three seconds.

Should the outside unit run when the AC is off?

Does The AC Fan Outside Always Run? The answer to this is no. The AC fan does not run non-stop. It's intended to cycle on and off, depending on the needs of the HVAC unit.

Why is my fan running when the thermostat is off?

Two problems that could cause your fan to run without stopping include: A bad fan limit switch that needs to be replaced. Bad thermostat wiring.

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.

Why is my thermostat not kicking off?

No power: If the thermostat isn't working at all, there could be a power issue. Try checking the circuit breaker box or replacing the batteries. Bad wiring: The thermostat may be unresponsive if the wiring has gone bad. Remove the cover and check inside for loose, detached, or corroded wires.

Why is my outside AC unit always running?

Your refrigerant needs to be replaced or refilled. The AC condenser is dirty. The evaporator coils are frozen. There's an issue with the AC fan itself.

Why is my AC fan running when AC is off?

If only the fan is running when the AC isn't, there may be a faulty relay switch stopping the settings you enter on the thermostat from being communicated to the fan. It's also possible there is another wiring issue or short circuit preventing the on and off commands from going to your fan.

Can the AC run without the outside unit running?

A central AC system consists of indoor and outdoor units. An indoor air handler can continue running when the outside unit has shut down. While air will blow from the vents, it won't be cooled; it may be as warm as the summer air outside.

Why won t my outside AC unit turn off?

Stuck Compressor Contactor

This is one of the most common reasons why condenser units won't shut off. The contacts of a contractor can become pitted over time and wear down. In many cases, the contacts stick together or weld shut in a closed position, preventing the outdoor unit from shutting off.

How long to leave AC unit off to reset?

Shut off your system by hitting the isolation switch, wait 30 to 60 minutes and then turn it back on. This manual reboot fully disconnects your AC unit from power, allowing all electrical components to reset.

Where is the reset button on a carrier outside AC unit?

FIND THE RESET BUTTON

In most cases, the small red reset button is inside the AC's compressor. If unsure, you can always refer to the user's manual to find the exact location.

Why does my outside AC unit run for a few minutes then shut off?

Air conditioning is meant to come on and stay on for at least 10 to 15 minutes, often much longer. If your AC continues to turn off after 15 minutes or less every single time, or even just minutes after it first kicks on, your unit is “short cycling.” This means you may need repairs to your air conditioning unit.

Why does my AC sound like it's running when it's off?

One possibility is that the contactor relay switch may not be working correctly. This component controls how the electricity gets to the compressor. If it's malfunctioning, power and amperage may be impacted, and you may hear the buzzing sound. The easiest fix is usually to replace the contactor relay switch.

How do I stop my air conditioner from running constantly?

What you can do:
  1. Turn your air conditioner off.
  2. Remove and inspect your HVAC filter. ...
  3. Ensure your filter isn't too restrictive and meets manufacturer recommendations.
  4. Clean/replace dirty or clogged filters as necessary.
  5. Install or reinstall new filter (ensure you install it to face the correct direction).

Why is AC running when thermostat is off?

Air conditioners have a number of electrical components. A stuck relay switch allows an electrical circuit to remain closed, constantly providing power to the air conditioner. The compressor contactor can fuse in a closed position, allowing the condenser unit to keep on running with constant power.

Why is fan running if thermostat is off?

Incorrect settings on your thermostat or fan limit switch can cause the fan to run continuously. Faulty wiring or a broken fan limit switch can also cause your fan to keep running. You can diagnose and fix some furnace fan issues on your own. Faulty wiring or a broken switch will require professional repair.

Why won't my AC stop running?

If your air conditioner will keep running no matter what repair you try, malfunctions or faulty components are to blame. You could have a dirty air filter, clogged condenser coils, frozen evaporator coils, a broken relay switch, or a bad thermostat, amongst other common air conditioner issues.

Previous article
Should I mist my snake plant?
Next article
Will roaches get in your bed?