Honeywell Thermostat Cool on Blinking (How to Fix)

Has the Cool On light on your Honeywell Thermostat begun to blink? Don’t be concerned. Read this tutorial to learn how to solve the Honeywell Thermostat Cool On flashing.

Worry not

Sometimes, in situations like this, users can get upset or frustrated at their devices failing to work properly. But this issue is a lot more prevalent than you would believe. 

In reality, in 90% of situations, it won’t be a significant issue. It’s only one of the Honeywell Thermostat’s ‘features.’ The only time you should be concerned is if it happens regularly. 

What is the purpose of the Honeywell Thermostat’ Cool On’ Blinking? 

Honeywell Thermostat "Cool On" flashing

As previously stated, in the great majority of circumstances, this will not be an issue. That indicator will most likely be blinking because your Honeywell Thermostat has momentarily lost electricity. 

The blinking light indicates that one of the unit’s safety measures is operational. It’s attempting to give the compressor in your system enough time to cycle before reactivating. 

This simply implies you won’t kill the AC compressor, which may be rather expensive to replace. It’s acceptable if this is a one-time occurrence and the light does not blink for more than five minutes. 

There’s nothing to be concerned about. And there isn’t anything that needs to be fixed. However, if the problem persists or if the indicator never blinks, you’ll need to conduct some troubleshooting. 


You should follow the steps as they are listed below. The reason why is because the first step is simpler and might fix your issue instead of moving on to a more complex step that might not resolve your issue.

Examine your circuit breakers. 

If there is a power outage, the Honeywell Thermostat will blink as stated. As a result, we recommend that you check your HVAC system’s circuit breakers. 

It would be best if you double-checked that nothing was triggered. If anything has happened and continues to do so, you should consult an HVAC specialist since this might signal that something is amiss with your system. Although luckily, it will be pretty unusual. 

Restart the system as a whole. 

If the light hasn’t ceased flashing after five minutes, we recommend that you switch off everything in your system. 

Turn it off for a couple of minutes before turning it back on. This can occasionally result in a complete system reset, which resolves the problem. 

The majority of individuals report that the issue has been appropriately resolved at this stage.

Check the Honeywell Thermostat’s Batteries 

The flashing light indicates that the thermostat is unable to deliver a cooling signal to the air conditioner in some instances. 

While there might be a variety of causes for this, it’ll likely be anything as simple as your thermostat’s batteries needing to be replaced. 

This will be a fast task. If you’re unsure how to change your thermostat’s battery, reference the handbook. 

This will lead you through the entire procedure. But keep in mind that every Honeywell Thermostat is unique. 

Certain Honeywell Thermostats only include a battery as a backup power source. The main source of electricity will be your main supply. If that’s the case, you can go forward to the next step. 

Drop the temperature

Reduce the temperature on the thermostat to the lowest setting possible. Some customers have claimed that simply setting their thermostat to the lowest attainable temperature was enough to activate the device. 

You may have to wait another five minutes for the light to turn off. However, you may ultimately notice a difference in temperature. 

At this point, the ‘Cool On’ light will cease flashing. Yet, if Honeywell Thermostat Cool On flashing does not stop, continue into the next step.


Much like your dirty clothes need to be washed every so often, your AC needs to be taken care of. Build up of dirt and other particles are likely since the AC pulls air from outside your home and is then filtered.

Clogged AC filters
Honeywell thermostat

If you haven’t had your air conditioner serviced in a while, you should clean the filters. The air conditioning cannot work correctly if the filter is clogged.

As a result, the Honeywell Thermostat will struggle to relay the cooling signal to the air conditioner. The light will continue to flicker as a result of this. 

Don’t panic if this is your first time cleaning your AC filters, as it’s a relatively straightforward task. Because the technique differs from one air conditioner to the next, you’ll need to reference the handbook. 

If you haven’t cleaned or replaced your AC filters in over a year, it is recommended to change them rather than clean them.

Clean the coils on your air conditioner. 

The same for the filters may be said for your air conditioner coils. These are a little more difficult to clean, but you should be able to handle them yourself. 

If you’re unsure how to clean your coils, see your AC’s instructions. This is a task that you must complete at least once a year! It should be included in your annual maintenance with an HVAC specialist. 

The Honeywell Thermostat should be reset. 

If the Honeywell Thermostat Cool On Flashing continues to flicker after completing the prior instructions, you can try resetting it. 

This is a long and winding procedure, which is why I put it towards the end. Because the method varies from the Thermostat to Thermostat, you should always reference the instruction manual for your particular model. 

Make a note of any settings before resetting the system to make the procedure go a little smoother. It will make getting things back up and running a lot easier for you. For instance, you might have to dim Honeywell T9 Thermostat once again after it is reset because it will return to a factory default state.

Seek the advice of an HVAC technician. 

If you’ve followed all of the procedures and the light is still flashing, there’s not much more you can do. Your only option is to contact an HVAC specialist to see if they can diagnose the issue. 

It might be a problem with the power supply, or it could be a problem with the air conditioner that you can’t fix yourself. 

In short 

As you can see, repairing a Honeywell thermostat that is flashing ‘cool on’ isn’t difficult. Most of the time, all you have to do is wait five minutes or so. 

If it doesn’t work, many troubleshooting options are available to you. The issue will be resolved at some point along the route. 

It’s quite unlikely that you’ll need to consult a professional to solve a problem. But if it gets to this point, you can contact Honeywell’s customer service to discuss what could be done regarding your device.

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