Why Is My Thermostat Blinking?

Thermostat blinking but no air coming out

If you’re like most people, any time lights start blinking around you, you’re going to be a bit alarmed. It’s one thing when those lights are something you’re familiar with, such as your alarm clock or car hazard lights, but it’s another when it’s something unfamiliar like your thermostat is blinking.

Why Is My Thermostat Blinking "Cool On" But No Air is Coming Out?

If your thermostat is blinking, there is likely a problem with the battery. The blinking is used as an alert that it's time to replace it before the battery dies. If it continues to blink after you've changed out the battery, there may be a bigger problem with your thermostat.

Another reason your thermostat may be blinking is that you have a problem with your outdoor unit.

Problem with the Outdoor Unit

If you see a flashing light on your thermostat, that's a signal that there’s a problem with your outdoor unit. When this happens, your outdoor unit will shut off and send a signal to your thermostat, causing it to blink. Thing is, that signal doesn’t mean your indoor unit is made aware of the problem. Your indoor unit will probably continue running and the thermostat will keep blinking until the problem is fixed.


Most often, you’ll need to shut off your indoor unit for a minute, then turn it back on after 30 seconds, causing the light to turn off as well. Wait about 10 minutes, then check to see if your outdoor unit has turned back on.

  • If it has, the problem was probably with the circuit breaker.
  • If it hasn’t, there is probably a bigger problem, and you should call an HVAC professional to inspect your unit.

Pro Tip: Try to count how many flashes happen in one sequence — these are often codes that indicate what the problem is.

Why Is My Thermostat Blinking "Cool On?"

If your AC is not blowing any cool air but your thermostat is blinking "Cool On" it likely just means that the temperature inside your home matches what your thermostat is set at.

Because your AC no longer needs to push out cool air when the temperature matches what the thermostat is set for, it creates a time delay and your compressor shuts off.


To test that this is what is causing your thermostat to flash "cool on," you can lower the temperature on your thermostat by a few degrees. If the blinking message stops and your unit kicks back on, there's nothing more to do. However, if you notice that your AC has stopped cooling or that it is cycling frequently, it could be that your AC is short cycling and needs to be repaired

Call Now for Thermostat Service in Fairfax

Many HVAC issues are the result of a bad thermostat. If you have noticed that you are constantly having to adjust your thermostat or that it’s always blinking and your AC isn’t blowing cool air, chances are it should be serviced. At Air Treatment Company, we have the expertise needed to diagnose any and all problems you may have with your HVAC system and offer comprehensive thermostat repair and installation services. We install only quality brands so that you can enjoy reliable home comfort.

For more information or to schedule a thermostat or AC service appointment, give us a call at (703) 270-0881 or contact us online.

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