Dealing with a Honeywell thermostat flashing “cool on” but not cooling your home? We get how annoying that blinking light can be.
But don’t call the repair guy just yet – a flashing “cool on” is a common issue that you can often resolve yourself with some simple DIY troubleshooting.
In this guide, we’ll walk you through the likely causes, from low thermostat batteries to AC malfunctions. We’ll also provide tips to get your Honeywell thermostat back to properly controlling your home’s temperature again.
No technical skills are needed -just follow our handy hacking guide to get that stubborn blinking “cool on” light sorted out in no time!
Why is my Honeywell Thermostat Blinking Cool On?
Seeing the “Cool On” light blinking on your Honeywell thermostat? Don’t stress, this is a common issue that usually has a quick fix.
A flashing or blinking “cool on” light typically means one of the following:
Five-Minute Compressor Delay
The most common reason for a Honeywell thermostat “cool on” blinking light is that the AC compressor needs 5 minutes to restart safely after a power interruption.
This delay allows the pressure inside the AC system to equalize before the compressor turns back on, preventing damage.
It is perfectly normal for the “cool on” light to flash for up to 5 minutes during this process. Once the delay period ends, the light will stop flashing and your AC will resume cooling.
Low Thermostat Batteries
If the batteries powering your Honeywell thermostat are running low, this can cause operational issues like the Honeywell thermostat “cool on” flashing light.
The weakened batteries struggle to maintain a consistent power supply to your thermostat. This prevents it from communicating properly with your AC unit.
Replacing old or dying batteries with a fresh set typically stops the blinking issue.
A recent power outage in your area can force your AC compressor and Honeywell thermostat to reset.
The restart process initiates the 5-minute compressor delay, causing the “cool on” light to flash temporarily. If the light flashes longer than 5 minutes, you may need to reset the furnace circuit breaker.
AC Unit Malfunction
An underlying issue with your AC system itself can manifest as a flashing “cool on” light on your Honeywell thermostat.
Problems like a faulty capacitor, bad blower motor, clogged air filter, blocked condenser coils, refrigerant leaks, electrical faults, and more can interfere with the thermostat’s operation.
Incorrect Thermostat Settings
If your thermostat temperature, mode, or other settings are incorrectly configured, this could cause a falsely flashing “cool on” light. Always double check the thermostat is set properly.
Loose Wire Connections
Electrical wiring that has come loose from the thermostat terminals can cause connectivity issues that result in a blinking “cool on” light. Check wires are securely attached.
Rapidly switching your HVAC system from heating to cooling mode puts a strain on the compressor. A flashing “cool on” light indicates the 5-minute restart delay kicking in.
Faulty Thermostat Wiring
Incorrect or loose wiring between the thermostat and AC unit can cause intermittent communication issues that make the “cool on” light flash.
A blown fuse cutting power to your AC compressor can make the thermostat blink “cool on” as it tries to call for cooling.
Not enough refrigerant pressure in the AC system prevents cooling, leading to a flashing “cool on” light.
How to Fix Honeywell Thermostat Cool On Blinking Light
Determined to get your Honeywell thermostat to stop blinking “cool on”? Don’t call the repairman just yet. In most cases, you can easily troubleshoot and fix this issue yourself with the following DIY tips:
1. Lower Thermostat Temperature
To test if your thermostat and AC are functioning properly, lower the temperature as low as it will go.
Ensure the thermostat is set to “cool” and the fan to “auto”. Let it run for 1 hour and feel if cool air starts blowing. If not, continue troubleshooting.
2. Check Thermostat Batteries
Weak batteries can’t power the thermostat properly leading to operational issues like flashing “cool on”.
Replace old batteries immediately when you see the low battery warning. Insert fresh AA alkaline batteries in the correct orientation.
3. Inspect Electrical Wiring
Loose wire connections from the thermostat to the AC control board can interfere with communication.
Detach wires one at a time and reconnect them firmly to ensure a tight fit. Refer to your model’s wiring diagram.
4. Reset AC Circuit Breaker
If you’ve had a recent power outage, resetting the air conditioner circuit breaker may be required to restore power.
Switch the breaker off and on again. Wait 30 minutes before resetting it again if needed.
5. Replace AC Filter
A clogged, dirty air filter blocks airflow and strains your AC system. This manifests as thermostat errors.
Replace filters monthly or clean with a vinegar/water solution.
6. Clean AC Condenser Coils
Outdoor condenser coils blocked with dirt, leaves, and debris lead to reduced cooling capacity.
Carefully clean the fins and coils annually for maximum airflow.
7. Verify Thermostat Settings
Ensure the thermostat mode, temperature, and fan settings match your preferences. Incorrect settings cause the thermostat to function improperly.
8. Reset Thermostat
If all else fails, reset your Honeywell thermostat. Press and hold the “Menu” button for 10 seconds, then select “Factory Reset.” You’ll need to reconfigure it after this.
9. Check Refrigerant Charge
Using a gauge, check if the AC refrigerant level is in the normal range. If it’s low, top it up. Low refrigerant can disrupt cooling.
10. Clean Blower Assembly
Remove and clean the blower motor, fan blades, and housing to optimize airflow. Dirt buildup inhibits cooling efficiency.
11. Verify Jumper Settings
Check if the thermostat jumpers match your HVAC system type. Incorrect configuration can cause heating/cooling issues.
12. Tighten Wiring Connections
Inspect wiring terminals on the thermostat and AC control board for looseness. Tighten all loose connections.
13. Cycle AC Unit Power
Turn off the power to the AC unit for 30 seconds, then turn it back on to reset the system and see if the “cool on” flashing light stops.
14. Call A HVAC Technician
For recurring flashing “cool on” light issues that you cannot resolve, contact a professional HVAC technician to troubleshoot and fix the problem.
How to Prevent Honeywell Thermostat “Cool On”
Tired of dealing with that pesky flashing “cool on” light on your Honeywell thermostat? The best solution is to prevent the problem in the first place.
Follow these proactive maintenance tips to stop the blinking before it starts:
Replace Batteries Regularly
For battery-powered models, replace thermostat batteries at least once annually to prevent low battery conditions that can cause blinking “cool on”. Buy high-quality alkaline batteries to maximize lifespan.
Tighten Wire Connections
Open the thermostat cover annually and check wiring terminals for loose connections that may degrade over time from vibrations, corrosion, etc. Tighten any loose wires.
Clean AC Filter Frequently
Clogged, dirty filters lead to HVAC airflow obstruction that manifests as thermostat errors and blinking lights. Replace filters every 1-3 months for optimal performance.
Clean AC Condensate Drain
Drain line obstructions from algae, slime, dirt, etc. can cause water overflow faults that disrupt AC operation and create thermostat issues. Keep drains clear.
Inspect AC Coils
Clean external AC condenser coils before dirt and debris accumulation leads to restricted airflow and reduced cooling capacity which stresses the thermostat.
Verify Refrigerant Charge
Check refrigerant levels annually and recharge your AC system as needed to prevent low pressures that lead to cooling problems and thermostat malfunctions.
Check Air Ducts
Ensure supply and return duct work is clear of obstructions like dirt, nests, closed vents, etc. that can hamper airflow and create AC system strain, manifesting as thermostat errors.
Lubricate Fan Motor
Annual motor lubrication maintains optimum blower fan efficiency. Reduced airflow from a strained fan motor affects HVAC performance and thermostat function.
Proactively test and replace the AC capacitor as needed to prevent failure that can interfere with the compressor starting and cause a flashing “cool on” display.
The flashing “cool on” light on your Honeywell thermostat means that there is a problem with your HVAC system that is preventing proper cooling.
The blinking indicator could be something as simple as low batteries or a tripped circuit breaker. But it can also indicate more serious problems like refrigerant leaks, electrical faults, or unit malfunctions that require professional repair.
If left unchecked, a persisting flashing “cool on” light can lead to system strain, higher energy bills, and costly HVAC component failures.
In order to prevent these risks, you need to follow the troubleshooting instructions outlined in this guide to help you diagnose the root cause.
With some diligent DIY maintenance and repairs, you can fix the blinking light problem and restore smooth, efficient cooling.
By taking action to properly maintain your Honeywell thermostat and HVAC system, you can prevent frustrating “cool on” blinking episodes this summer and keep your home comfortable.
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