Why Is My Honeywell Thermostat Flashing Cool On?

When you have thermostats in your house, you will come across terms like COOL ON or HEAT ON blinking. But do not panic when you see these indications blinking. Today’s article talks about the reasons behind the blinking of COOL ON. 

When COOL ON blinks, it usually indicates a cooling system delay. But when it flashes for over 5 minutes, the primary reasons are power outage, sensor issues, wrong thermostat settings, low batteries, dirty filters and coils, wire problems, and wrong mode selections.

If you have ever faced a problem and are searching for solutions, this is the right place. We have covered all the possible reasons behind the blinking of COOL ON and provided some easy solutions. So stick till the end. 

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What is the COOL ON indicator in the Honeywell thermostat?

Usually, the COOL ON indicator in the Honeywell thermostats should not be alarming. 

It is expected when the air conditioner delays providing cool air into the room. It will blink for only 4 to 5 minutes. 

The delay gets triggered to protect the HVAC system from short cycling

When it blinks the COOL ON, you will see a SNOWFLAKE icon on the thermostat’s screen. 

When the indicator stops signaling after 5 minutes, it indicates that the cool air is restored and the HVAC will function normally now. 

How long the indicator should blink is a crucial factor here. 

It is alarming when the indicator blinks for more than 5 minutes.

Some common reasons behind the problem include:

  • Wrong mode setting
  • Wrong thermostat setting
  • Low batteries
  • Power outage
  • Faulty sensor 
  • Clogged filters and coils 
  • Switching from cool mode to hot mode 

Let’s learn how these issues make the COOL ON indicator of the Honeywell thermostat blink for more than 5 minutes.

Thermostat Mode settings

Wrong thermostat mode settings can make the COOL ON blink.

When there is a power outage in the HVAC system, it will turn the thermostat settings automatically to SET UP MODE, and the device requires a reboot.

When this happens, the thermostat will automatically start blinking the COOL ON indicator for more cool air. 

Fix the SETUP MODE and the clock settings with the user manual’s help to fix the problem. 

Turn off the device for some time and turn it back on again if you don’t know how to get to the regular cooling mode.

Set the thermostat to the COOL MODE and the fan to the AUTO MODE. 

Thermostat settings 

Another problem is the temperature setting. 

When the COOL ON blinks, the device cannot control the cooling. 

To fix this, set the temperature to the lowest and set it to COOL. 

Also, keep the fan setting to AUTO.

Wait for at least 45 to 60 minutes to see if the cool air gets pumped out of your air conditioner. 

Low batteries 

The status of the battery in the thermostat plays a significant part in the blinking of the COOL ON indicator. 

If the batteries have low power, the thermostat won’t be able to detect the surrounding temperature. 

As a result, the heating or cooling systems won’t work correctly, leading to COOL ON blinking.

Look for a BATTERY LOW indicator on the thermostat’s screen. 

Change the Honeywell thermostat’s batteries once a year or every 10 months.

Open the battery compartment and replace both batteries with AA or AAA alkaline batteries. 

You will also see the COOL ON mode after you change the batteries. 

But that will be for a few minutes. 

After the thermostat settles down, it should disappear.

But, if you have a 24 VAC-powered battery, it won’t have any batteries. In that case, you will need to check the wire connections. 

Also read: 9 Reasons Your Honeywell Thermostat Not Turning On

Wiring issues 

Incorrect or loose wiring is one of the common mistakes made by beginners. 

So, when your thermostat is blinking the COOL ON, check the wiring.

Loose or incorrect wiring leads to malfunctioning of the thermostat, COOL ON being one of them. 

The device cannot detect the temperature correctly and shows the COOL ON indicating a delay in the cool air. 

So, start investigating the wire issues in your thermostat:

  1. Turn off the thermostat’s power and also the breaker.
  2. Remove the cover plate and check the wire connections.
  3. If they feel loose, tighten them.
  4. Along with that, check the terminals. 
  5. Please put them in the correct terminals for adequate functionality. 

Also read: What Happens If You Wire A Thermostat Wrong?

Bad blower motors

The cooling system’s blower motor is responsible for your house’s airflow. 

It negatively affects the cooling unit when it goes wrong.

The blower lasts for only 12 years. 

So, the blower motor is the culprit when your Honeywell thermostat is malfunctioning. 

When the thermostat tries to turn the blowers on but fails, it blinks the COOL ON. 

Here, you need professional help. 

Working with these delicate HVAC components is risky. 

Experts can handle them professionally and fix them quickly. 

The cost will be an average of around $450, which is expensive. 

But it is better than doing it yourself and increasing the damage and cost. 

Dirty air filters

Here the air filters of the HVAC system are the problem. 

When the air filters become dirty, the air gets trapped inside. 

As a result, your house does not receive enough air at the desired level.

Therefore, there is a delay in the cool air arrival in the house.

As a result, when the thermostat detects the room temperature, it blinks the COOL ON for more cool air.

So, you must keep your unit’s air filters clean to avoid this problem:

  1. Open the HVAC system and remove the air filter.
  2. Try to see through it. 
  3. If you cannot see through it, replace the filter with a new one.
  4. If the filter is reusable, wash, dry, and reinstall the filter
  5. While installing, make sure to adjust it towards the arrow’s direction.

Change the air filters every 3 to 4 months to prevent the problem. 

Ignoring the problem can lead to expensive issues.

It is better to spend $10 every 3-4 months than call a professional when the problem increases and spend $40 to $50.

Dirty coils

Dirty coils of the HVAC system are also responsible for the thermostat’s blinking of the COOL ON. 

It also restricts the cool air and does not make your house comfortable enough in the summer. 

As a result, the thermostat will constantly blink the indicator for the delay of the cool air. 

When the condenser is outside, it gets dirty faster due to the twigs, dirt, debris, and dry leaves. 

To fix the problem, clean the air coils from time to time. Since the coils are fragile, it is better to call a professional to clean them. 

Electrical or power supply issues

Power outage is the primary electrical issue when the thermostat blinks the COOL ON indicator. 

You need to check the unit’s power supply for the HVAC systems to work correctly. 

Without enough power supply, the unit will malfunction and fluctuate.

The HVAC systems will need enough power to function well. 

It cannot provide enough air to the room with insufficient or unstable power.

The system gets interrupted. It triggers the thermostat’s compressor to restart and activates the COOL ON when the cool air gets delayed. 

To fix the problem, you must look over a few things:

  1. Check the power connection of the unit. 
  2. Check the switches, sockets, power suppliers, and connectors. 
  3. Check the internal and external components of the unit and see whether they are appropriately connected and receiving enough power.
  4. Examine the breakers and restart them by turning them off and on again.
  5. If there are any blown fuses, call an expert to replace them. For tripped breakers, flip the switch back to the on position.
  6. Call a professional for further assistance. 

Also read: 11 Reasons Why Your Honeywell Thermostat Is Blank

Dirty or faulty sensors

The sensor inside the thermostat is what detects the surrounding temperature. 

So, if the sensor is at fault or dirty, the device cannot detect the correct temperature of the room. It can lead to wrong readings.

Furthermore, the thermostat sends the wrong signals to the HVAC systems. 

You may not receive enough cool air. 

So, the thermostat will blink the COOL ON indicator, indicating insufficient cool air. 

So, if your thermostat sensor is dirty, clean it with a cloth or brush. 

If it is faulty, replace it with a new one with a professional’s help. 

Switched from COOL MODE to HEAT MODE and vice-versa

Many Honeywell thermostats have auto-adjustable heating and cooling features where the thermostat automatically shifts from one mode to another based on the room temperature. 

If your surroundings are cold, the thermostat’s mode will change to HEAT, and when the surroundings are hot, it changes to COOL.

At such conditions, sometimes the thermostat will blink the COOL ON mode for the delay in the cool air when you suddenly switch to the COOL MODE. 

The HVAC will need time to settle down and provide enough cool air. 

So, fix the setting:

  1. Go to the thermostat. 
  2. Access the touch screen and set the temperature mode.
  3. Adjust the desired cooling or heating.
  4. Wait for a few seconds. Once your room receives cool air, the blinking should turn off.

Should I reset my thermostat?

When no troubleshooting step works, resetting the Honeywell thermostat is the best method to fix the problem. 

It restarts all the features, and the device generally starts working as before. 

To reset your Honeywell thermostat:

  1. Go to the touch screen.
  2. Go to the MENU or HOME SCREEN. 
  3. Press the side arrow until you find the RESET option.
  4. Press the option and click on FACTORY RESET. 
  5. Confirm and wait for a few minutes for the device to come back.

Remember that once you FACTORY RESET the device, you must set all the previous set features again.

When should I call a professional?

Calling a professional should be your last resort when nothing fixes the COOL ON blinking problem. 

The problems mentioned above behind a COOL ON blinking for more than 5 minutes are the possible problems. 

So, you can solve them with the solutions I have explained with each problem. 

But if you fail to solve them despite following the proper steps, there is some serious issue.

Therefore, I suggest you call a professional. 

Your device might have complex technical issues, such as an open switch on the outside unit, excessive defrosting, or compressor or condenser failure. 

So, these problems need a professional’s attention. 

Along with these, problems like faulty sensors or damaged wires also require a professional. 

Final thoughts 

The Honeywell thermostat in your house will act as the HVAC system’s control panel. It detects the surrounding temperature and sends signals to the HVAC system to give you the desired temperature when you set it.

The COOL ON indicator blinking is usual if that is only for 4-5 minutes. But more than 5 minutes is abnormal. Common issues include power outages, dirty coils and filters, faulty or dirty sensors, wrong thermostat settings and mode selections, low batteries, and wire issues.

Each can be fixed individually, but if you can’t, factory reset your thermostat. It works best when nothing works. But if the problem persists, call a professional for help because the thermostat or the HVAC might be dealing with some complicated issues which only an expert will know and fix.

Why does the Auxiliary pump display the COOL ON blinking?

When the HVAC blows hot air, but your thermostat is set to low temperatures, the problem is in the wiring, or the AUX heat is connected to the heat pump. It confuses the heater and activates the COOL MODE. Ensure the heating wire is connected to the W1 and W2 terminals.

Should I reset my Honeywell thermostat during a power outage?

Honeywell thermostats contain in-built memory storage to store schedules, programs, and customizations. So you do not have to reset the thermostat after a power outage. It will automatically restore the old settings when the power comes back.

Reference: Thermostat Wikipedia

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Arthur Smith

Howdy! I am Arthur Smith, an electrical engineer who is extremely passionate about electronics. I have lived in different parts of the US and currently reside in Wisconsin. I am one of those rare children who knew what he wanted to study and do in life right from the start. I was a curious child who wanted to know how switches work and how the AC works, and I would always observe my dad whenever he would handle the wires and fix things around the house. I currently work as an electrical engineer at a reputed company and write for this blog. And I read loads of books or play video games in my free time.

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