Home-How » 7 Reasons Why Honeywell Thermostat Cool on Flashing (Solved!!!)

7 Reasons Why Honeywell Thermostat Cool on Flashing (Solved!!!)

We all know how frustrating it can be to turn on our air conditioners and not get enough cool air. It is even more annoying when the problem is not with the cooling system but the thermostat. Do you have a problem with your Honeywell thermostat ‘Cool On’ flashing? You are not alone.

It is not unusual to find the Cool On flashing on your thermostat, although it tends to happen at the wrong times. Fortunately, there are some troubleshooting steps for checking the source of the problem and repair steps you can take. This article explains the possible causes of the thermostat malfunction and how to fix it.

Why Does The Cool On Indicator Flash?

Typically, the Cool On indicator flashing on your Honeywell thermostat should not be alarming. Sometimes, the indicator flashes when the air conditioner prepares to turn on the cooling function and release cool air.

The indicator flashes for about five minutes or less before it stops and cooling resumes. The timing is crucial because it indicates that the compressor and other internal components are cycling to prevent possible damage. It is a delay mode to get the system up and running.

Power Interruption

It usually happens with a power outage or a minor system malfunction. In other words, it is designed to protect the air conditioning system. However, it becomes a problem when the flashing icon continues beyond five minutes.

It means there is a more serious issue than the system trying to protect itself. Therefore, you must troubleshoot and find the source. Only then can to fix it to prevent a total system shutdown.

Troubleshooting and Fixing a Honeywell Thermostat Cool On Flashing

Troubleshooting and Fixing a Honeywell Thermostat Cool On Flashing

Before taking any complex step to fix this problem or hiring a technician, try fixing it yourself. There are simple steps to try, and they usually work, especially if the thermostat is in good working order. Start from the simplest ones and move to more complex issues.

1. Check the Power Supply

As mundane as it may sound, checking the power supply to the AC unit is a priority. You may assume there is power, but the air conditioner may malfunction if the power supply is inadequate or fluctuating.

An air conditioner requires a lot of energy to function, so it usually runs on a dedicated outlet and circuit. Inspect the circuit breaker outside the house controlling the unit; it must be on, and there must be no blown fuse. Check the disconnect switch next to the outdoor condensing unit to ensure it is on, and the unit is running.

You may find another switch next to the indoor unit depending on your brand. Ensure the switch is on; toggle it to see if the unit responds. Additionally, listen for odd sounds that may indicate an internal problem and trace it. Then, you can hire an HVAC system professional for further assistance.

2. Ensure the Mode Setting Is Correct

The next thing to check is the mode of operation. If you want your air conditioner to produce cool, you must set the mode to Cool, adjust the fan speed, and set the correct temperature. There are different modes of operation for every air conditioning unit, and you must select the right one for the system to run optimally.

If the thermostat display has a blinking indicator and time, the device may be in Setup Mode. The mode is usually triggered when there is a power interruption, and the thermostat needs to reboot. It causes the device to flash, and correcting the mode and time should fix it.

Therefore, follow the instructions on the user manual or check the screen for prompts to stop the flashing issue and get cooling back. Turn off the thermostat for a few minutes and turn it on again if you are unsure how to get it back to the regular cooling mode.

3. Adjust the Settings

The next step is to adjust other settings on the thermostat. If you have corrected the mode of operation and set it to Cool, you must ensure the fan setting is on Auto and the speed matches the cooling mode. Setting the fan to On makes it run constantly, which affects the system’s optimal performance.

Next, set the temperature. If you want the best cooling, the temperature should be a few degrees lower than the current room temperature. However, set it to the lowest point for troubleshooting purposes. Afterward, wait for the air conditioner to run and check how well it cools.

If there are no internal issues with the thermostat and air conditioner, the AC system should resume its normal cooling function at this point. Place one hand before the supply vents and see if there is a draft of cold air. If there is none or it takes too long to come, and the thermostat continues flashing, continue to the next step.

4. Test the Batteries

Test the Batteries

Now is the best time to check the status of the Honeywell thermostat batteries. It may be time to replace them, especially if you have used the thermostat for more than one year. In other words, the thermostat may malfunction in more ways than one if the batteries are old or worn out.

Therefore, turn the device off and open the battery compartment to check the batteries. You may have to remove them from the thermostat. Try rubbing them gently between your hands or inserting them into another device. But the best step is to replace them with the correct battery type for the thermostat.

Not all Honeywell thermostats use batteries; some are 24-VAC powered, which means they run on electricity. If you have one like that, the problem may be with the internal wiring or low battery malfunction. Unless you have the training and skills to check the wiring, it is best to hire a technician to check and fix it if necessary.

5. Inspect the Air Filter

While we do not usually think of the air filter in our air conditioners, it is one of the most vital parts of the system. The filter can improve the system’s performance or cause extensive damage when clogged with a significant amount of dirt.

If the Cool On indicator flashes on your Honeywell thermostat, turn the air conditioner off and inspect the filter. A clogged air filter restricts the airflow into and out of the system, causing a malfunction. When there is an air supply reduction, the cooling function fails. Then, the thermostat alerts you to the system malfunction.

Some AC filters are reusable; if your air conditioner uses this type, you can clean and reuse them. Others are disposable, and you must change them every month. However, all air conditioner filters must be replaced every two to three months for optimum system performance. Changing the filter may fix the Cool On flashing issue.

6. Clean the Condenser Coil

The coil, typically outside the house in the condensing unit, comprises fragile fins. They condense the refrigerant and transfer excess heat out of the system. In other words, it ensures the air conditioner does not overheat and cause cooling issues.

However, the coil’s location outside the house makes it easy to get dirty. Over time, dust, leaves, dead grass, and other debris clog it and compromises its capacity to remove it. Consequently, the heat remains trapped and affects the cooling system. That may be the cause of the Cooling On flashing.

Therefore, inspect the AC coil and clean it if necessary. You may need professional assistance to clean it because of the fins’ fragility. Consider hiring an expert HVAC technician for the job and checking other components in the condensing unit.

7. Perform a Reset

Perform a Reset

When all else fails, consider resetting the Honeywell thermostat. A reset should restore it to its factory settings, wiping all your configurations. If you choose this route, you must note special settings and add them again when you reboot the thermostat. Note that Honeywell has different thermostat models, so the reset methods may differ.

If your thermostat has a menu button, press it and hold it for seconds. You should see options for resetting the device; Select Factory Reset and tap Factory or Reset when the prompt shows on the screen. But if the thermostat is connected by a C-wire, turn it off and follow the instructions to reset and restart it.

Consult the user manual for the thermostat if none of these reset methods works for your thermostat. And if the manual is not readily available, look for online manuals or other resources for resetting the specific Honeywell thermostat model you own.


Your Honeywell thermostat acts as your air conditioner’s control panel. You can change the system’s function and manage other features without touching the remote. So, it can be frustrating if it develops a problem, even if it is the Cool On flashing on the screen.

Fortunately, troubleshooting the air conditioner can point you to the problem so you can fix it. This article is helpful for checking different parts, especially the air filter and condenser coil. You may opt for a professional technician to service the thermostat and air conditioner and fix any errors.

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