Honeywell Cool On Blinking : How to Fix It?

Is your Honeywell thermostat blinking “cool” and causing temperature control issues? This common problem with air conditioning systems may indicate an underlying issue. Learn how to address it and regain control over your thermostat’s functionality.

Honeywell Cool On Blinking

Honeywell Cool on Blinking : What does it Mean?

When your Honeywell thermostat displays “Cool On,” it’s indicating that your air conditioner is working to circulate cool air in your home. However, if this message persists for an extended period without any cooling, there may be an issue.

Sometimes, “Cool On” may flash briefly and then stop after five minutes, with cooling resuming. This is a normal internal safety feature, allowing the compressor to initiate the system’s components. It’s important to note that power interruptions can also trigger this warning message.

Troubleshooting Measures:

If five minutes have elapsed without any cool air from your vents, it’s time to troubleshoot the issue. While we suggest trying these troubleshooting steps initially, you can also opt to enlist the services of an HVAC specialist for a professional resolution.

Turn the Honeywell Thermostat Down to the Lowest Setting:

Start by checking if your system is set to provide cooling. Lower the thermostat to its lowest temperature setting to verify this. Make sure the mode is set to “Cool,” and the fan setting is on “Auto.” After making these adjustments, wait for at least an hour to see if cold air starts coming through your vents. If you don’t feel any improvement, continue with further troubleshooting steps.

Check your Thermostat’s Mode:

Check your thermostat’s mode

Sometimes, a Honeywell thermostat may be incorrectly configured, resulting in issues like the blinking “Cool On” message. This can occur after a power loss, causing the thermostat to enter “Setup” mode, necessitating adjustments.

If you find your system in “Setup” mode, take the necessary steps to correct the settings. Also, ensure that the thermostat displays the correct time. By ensuring the proper configuration of your system, you can resolve the issue swiftly.

If Necessary, Replace the Batteries:

Maintaining your thermostat’s functionality depends on the condition of its batteries. Low battery levels can trigger the blinking “Cool On” indicator on your thermostat, preventing it from starting cooling or heating.

To check the battery status, look for the “Battery Low Indicator” on the thermostat display. Typically, you have around two months of battery life left once you receive this notification.

Ensure that your AC Unit is Powered:

After completing the previous troubleshooting steps, verify that the entire system has power. Before checking both the indoor and outdoor units, confirm that your thermostat’s batteries are in good condition. Additionally, inspect all connections, plugs, and power sources to ensure they are properly powered and connected.

It’s crucial to listen for any unusual noises that could signal a problem with the system. Be sure to check the circuit breaker and consider utilizing power switches if available. Another option is to inspect for blown fuses in the system.

Verify the Air Filter:

A dirty or clogged air filter can cause various system problems, leading to higher energy costs and a shorter lifespan for your air conditioning unit. It’s generally advised to replace your air filter every three months. If you have pets or allergies, you might need to replace it more frequently.

Check the AC Coils:

The “cool on” message on your Honeywell thermostat could be a sign of dirty air conditioner coils. Dirty coils, like air filters, can significantly impact your cooling system’s performance and comfort. However, coil issues are often overlooked because they are checked less frequently than filters.

Over time, coils can accumulate dirt, obstructing airflow and causing potential system problems. Regularly inspect and clean these coils as needed. Additionally, it’s advisable to remove any dirt or debris from your system’s fins for optimal performance.


We hope this article has been helpful in addressing the “cool on” flashing issue with your Honeywell thermostat. We conducted extensive research to provide you with the best solutions. Your feedback and comments are always welcome in the section below, as there’s room for further discussion. Please share which actions helped you resolve the “cool on” blinking problem with your Honeywell thermostat.

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