Fixing Cool On Blinking Light in Honeywell Thermostat

Last updated on April 12th, 2024

Did you find the Cool On light Blinking on your Honeywell thermostat? It’s normal if it’s blinking for a few minutes. It’s just the thermostat’s way of protecting the HVAC system from damage. But if the Cool On light is blinking for more than 5 minutes, then it could be a matter of concern. An underlying issue could be at play.

In this article, we will find out exactly why there is a blinking Cool On light on the Honeywell thermostat. And since there’s no off switch to stop it from blinking, how do you turn off the blinking Cool On light? We will cover all of this in great detail.

Reasons for blinking cool on light

The Cool On light blinks in the period when the compressor shuts off and turns back on again. To avoid short cycling, where the compressor turns on immediately and off again without completing the power cycle. This could damage the cooling system.

To prevent that the Honeywell thermostat Cool On light is on for a few minutes. When this light is on, the compressor doesn’t restart until the light stops blinking. This is kind of a safety measure for the thermostat. The light should turn off in 5 minutes.

If the Cool On light stays on for more than 5 minutes, the reason could be one of the following:

  • The power goes off, and the HVAC system is automatically turned off. Cooling won’t restart until the power is back on.
  • You just abruptly changed the Honeywell thermostat mode from heat to cool or vice versa. The system takes a while to adapt to the sudden switch and might have to shut off for a bit to cool down.
  • When your thermostat is low on battery, the Cool On could turn on.
  • The filters in your air conditioning unit are blocked, and that’s causing pressure on the system.

There are ways to tackle these issues or any other that could keep the Cool On light blinking on your Honeywell thermostat. In the next section, we will discuss them in detail.

Ways to stop the blinking cool on light

Ways to stop the blinking cool on light on Honeywell thermostat
Ways to stop the blinking cool on light on Honeywell thermostat

If the Honeywell thermostat Cool On light has been flashing for a long time, there must be some error with the system. There are a few troubleshooting methods you can try to get the Cool On light off. All of these methods might not be effective. So, you’ll have to try and see which one works the best for your thermostat.

Now, let’s see the different ways to stop the blinking Cool On light on your Honeywell thermostat.

1. Check the circuit breakers

Check the circuit breakers
Check the circuit breakers

Circuit breakers are located in the main electric box of your house. They tend to trip when a sudden change in electrical signal occurs. If the circuit breaker for your HVAC system has tripped, it will cut off the power supply for the system. The compressor thus turns off. This activates the Cool On light, and it will turn off only when the compressor is running again.

So go can check the circuit breaker of your HVAC system. If it has tripped, switch it to the on position. In a few minutes, when the compressor is running again, the Cool On light will turn off on your Honeywell thermostat.

Switching the circuit breakers can also solve other issues, like:

  • A blank screen on the thermostat
  • The HVAC system is not cooling
  • The thermostat is not connecting to Wi-Fi

2. Check the thermostat batteries

Check the thermostat batteries
Check the thermostat batteries

Several Honeywell thermostat models operate on batteries. When the batteries are low, they cause issues like a blank screen or a blinking Cool On light. What you can do is replace the old batteries in your thermostat with new ones. Replace all the batteries with new ones. Don’t pair old and new batteries. Use all the batteries from the same company to avoid any output fluctuations.

3. Select the lowest possible temperature

This is not the most recommended way of resolving this error, but it has worked for several people. You should choose the lowest temperature on your cooling system and let the system achieve that temperature.

In some time, you should feel the cool air coming out of the vent. After this happens, the Cool On light should automatically turn off in a few minutes. This doesn’t make much sense, but it has previously worked for several people. So it’s worth giving a try.

4. Restart the thermostat

If you find that the Cool On light is stubbornly blinking, you can just restart the Honeywell thermostat. Switch the button from the heat/cool mode to the off mode. Give a few minutes, and then select the desired mode or previously selected mode.

This will successfully restart your Honeywell thermostat. Some even remove and re-insert the thermostat batteries to restart it, but that isn’t really necessary. The off switch will do the job.

5. Restart the HVAC system

There are several ways to shut off and restart the HVAC system, but the most effective ones are the circuit breaker and the power switch. You can switch the circuit breaker off and give the system a few minutes to shut off completely. And then you can switch the breaker on.

This will restart the entire HVAC system. The same goes for the power switch. Hopefully, resetting the system will get the compressor running smoothly, and that should turn off the Cool On light.

6. Clean air and AC filter

Clean the air filter
Clean the air filter

The air conditioning unit has air and AC filters. These filters accumulate dust and debris. So they need to be cleaned from time to time. It is recommended to get professional help to clean these filters. But you can also do it yourself if you know how to.

Once these filters are cleared up, the airflow in the system will be restored to normal. This should remove the pressure caused by the system. The thermostat will detect normal operation and turn off the Cool On light.

7. Clean AC coils

AC coils should be cleaned at least once a year. If you let a layer of waste build up on the insides, it could block the refrigerant flow. Sometimes, it’s the reason your Cool On light won’t turn off. You need to maintain these coils annually. You should refer to your AC manual for the correct way to clean the coils on your unit.

8. Reset the thermostat

Resetting the thermostat
Resetting the thermostat

If none of the above solutions worked for you, there’s only one thing left to try – reset your Honeywell thermostat. It’s a long process, and the method varies from model to model. You will also lose all the custom settings, and everything will be back to default. That’s why we suggest this only as a last resort.

Make sure you have noted all your custom settings before you reset so you can get the device up and running quickly.

9. Contact the HVAC technician or Honeywell customer care

Even after resetting if the Cool On light is still blinking on your Honeywell thermostat, there’s not much you can do by yourself. It’s time to get professional help. Contact Honeywell customer care or an HVAC technician for support.

They will do a house visit and troubleshoot the system with advanced tools and pinpoint the exact error. If the thermostat is faulty, you will have to replace it with a new unit altogether.


Most of the time, the blinking Cool On light on the Honeywell thermostat turns off in a few minutes when the compressor is ready to power back on. But if the blinking continues for a long time, you should interfere to resolve the issue. Most of the above-mentioned solutions are easy to follow. Try them out until you pinpoint the error and resolve it.

There’s always the option to call for professional help if you don’t want to go through the hassle.


Why is my Honeywell thermostat blinking temporarily?

Your Honeywell thermostat blinks temporarily when the Cool On function is on.

Why is my Honeywell AC not cooling?

Your Honeywell AC is not cooling because the compressor isn’t working to pump the cool air through the system.

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Siddhi Gurav

She is the editor and content writer at Smart Home Bulls. Siddhi merges her passion for language with SEO expertise. With 4 years of experience as a creative writer and a passion for smart home technology, she fits in perfectly at Smart Home Bulls. Her wide experience in content marketing has been an excellent addition to our team.

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