Troubleshooting a thermostat can be tricky between all of the messages and error codes that they display. Many homeowners have scratched their heads the words “cool on” flash on the display yet the thermostat won’t work. So, what does this message mean, and what can you do to fix it?
A thermostat can flash “cool on” without blowing air due to electrical surges and dying batteries. A “cool on” message can also appear if the thermostat logs out or times out on its own. Wait 5 minutes, restart your thermostat, and identify and replace fuse or wire damage to make it return to normal.
Thermostats can also flash a “cool on” message if it is working hard to produce cool air. This can happen even if there isn’t an event such as a power outage or electrical surge. Follow along as we explore the possible causes and solutions for a thermostat that flashes “cool on” but isn’t working.
Do You Need Your Thermostat Repaired or Reprogrammed?
Get free, zero-commitment quotes from pro contractors near you.
FIND LOCAL CONTRACTORS
Possible Causes
Every thermostat is different, but you can generally count on the same primary causing for a flashing “cool on” message. With that said, it is important to understand the problem because it will help determine your solution. Let’s take a look at the three main reasons your thermostat is flashing “cool on” but isn’t working.
Dying Batteries
You can often tell that a thermostat’s batteries are dying when they start acting strangely. A flashing “cool on” message is a great example of such strange behavior, and it is often at the root of the problem. Thermostat batteries last up to 12 months, but they can die before then.
Dying batteries can cause thermostats to malfunction and display icons, error messages, and inaccurate numbers. The same can happen if you use the wrong type of battery for your thermostat. A thermostat can only work without batteries if it is wired to your home’s power, and even then they still require internal batteries.
Power Outage
Power outages are bad news for any appliance that runs on electricity, and it renders them useless. This is a big deal when it comes to HVAC systems and thermostats. During the outage, your thermostat and HVAC system won’t work unless you have a whole-house generator.
However, thermostats are known to operate poorly in the aftermath of a power outage. An outage can cause a thermostat to display incorrect messages over and over, and it can be frustrating. “Cool on” messages may flash and your AC or furnace won’t run properly in many cases.
Delay Mode
Thermostats enter a delay mode when they are underpowered or after an electrical surge. Delay modes generally last for 5 minutes, but it varies between manufacturers. It can be frustrating if you want your thermostat to work and it continually displays “cool on” messages or other notifications.
However, this process is necessary and is built into thermostats to prevent compressor damage. It can be harmful to restart your thermostat when it is in cooling mode. Compressors exert pressure, and restarting a thermostat while it’s in delay mode can cause a harmful change in pressure.
Luckily, many thermostats have built-in features that prevent users from restarting during the delay period. Whether your thermostat displays a “cool on” or “delayed” message, you should leave it alone for at least 5 minutes.
Faulty Wiring
Installation can be tricky, and it is all too easy to make a simple mistake when it comes to wiring a thermostat. Faulty wiring sometimes waits to rear its head, and it causes a thermostat to malfunction. This includes flashing messages such as “cool on” or “delay” without the thermostat working otherwise.
Licensed electricians and HVAC professionals are best suited to wire thermostats. However, if you installed your own thermostat, you may want to double-check your wiring. Even the most experienced DIYers can make a wiring mistake, and it can hinder your thermostat’s performance.
Solution
Your solution varies based on why your thermostat is flashing “cool on” without working. If your “cool on” message began flashing right after a power outage, you can narrow down your solutions. Let’s take a look at the quickest and most reliable fixes when your thermostat flashes “cool on” but just won’t work.
1. Wait
Delay mode is the most common reason for a thermostat to flash “cool on” without working. This mode indicates that something is wrong and that your thermostat is protecting the compressor. Time is the first solution in this scenario, and you need to wait it out.
The delay period allows enough time for the pressure to balance out within the compressor. Delay periods prevent expensive repairs and irreversible damage that can happen when there is too much pressure in a compressor. After 5 minutes, the pressure generally returns to normal and the thermostat will allow you to reset.
Many thermostats automatically reset, but some may make you do it manually. If the flashing doesn’t stop and it won’t you reset, it can indicate that you need to troubleshoot in other ways.
2. Inspect Fuses
Power surges and outages can blow fuses, and that can throw your HVAC system out of whack. If your thermostat started flashing “cool on” after a power surge, you need to inspect the fuses. Blown fuses are easy to identify, and you will need to replace them.
Hire a professional electrician if you are inexperienced with electrical work. It only costs $30 or less to replace fuses on your own, but it is much safer to hire an HVAC professional.
3. Replace Batteries
Dead batteries are the easiest solution besides simply waiting out the delay period. Thermostat batteries last up to one year, but they can die before then. Monitor your battery life if your thermostat displays low battery warnings.
Not all thermostats warn you when your batteries run low, and you may have to replace them when it’s too late. Thermostats typically take AA or AAA batteries, and most of them have compartments meant for two. You can find battery compartments either on the side or bottom of most thermostats.
Some thermostats require that you remove the cover to replace the batteries. Either way, it takes 1-2 minutes to replace thermostat batteries. Replace your batteries and your flashing “cool on” message will disappear in many cases.
4. Rewire Thermostat
You may need to rewire your thermostat if there is visible damage or nothing else works. It is a great idea to hire an HVAC professional or electrician to rewire your thermostat for safety purposes. However, you can rewire a thermostat safely if you pay attention to the color-coded wires.
Related Questions
Why is my Nest thermostat blinking red?
A Nest thermostat blinks red when the battery is charging. It generally takes 1 hour for a Nest thermostat to charge the battery. Nest thermostats typically automatically charge the battery when it gets low before it drains completely.
What does “error” mean on a thermostat?
“Error” appears on a thermostat followed by a code to indicate a specific problem. The code that follows the word “error” refers to specific problems such as power surges, clogged air filters, and power outages. Thermostats typically come with a manual that lists and explains what each error code means.
Are smart thermostats worth it?
Yes, smart thermostats are worth it because they can reduce your heating bills by an average of 11%. Your cooling bills can decrease by 15%, and you can program them for maximum energy savings. They can keep help regulate your temperature without using too much energy.
Can a thermostat cause short cycling?
Yes, a thermostat can cause short cycling and it can increase energy bills. Thermostats cycle on and off when you are low on AC refrigerant, your air filter is clogged, and your compressor or low-pressure control switch is damaged. Replace these parts and replenish your refrigerant so that it cycles on and off in normal intervals.
Do You Need Your Thermostat Repaired or Reprogrammed?
Get free, zero-commitment quotes from pro contractors near you.
FIND LOCAL CONTRACTORS
Summing It Up
Thermostats display the message “cool on” and cease working after power surges and outages. The message generally means that the thermostat entered a 5 minute delay period to alleviate and balance the pressure in the compressor. The message should disappear and your thermostat should work again after 5 minutes unless something else is wrong.
A thermostat can flash “cool on” when the batteries are dead or dying. In this case, the thermostat will return to normal when you replace the dead batteries with fresh AAs or AAAs. Check to make sure that your fuses aren’t blown and wires aren’t damaged after a power surge.
Replace blown fuses and rewire your thermostat so that it will work properly. A thermostat that flashes “cool on” and briefly stops working generally isn’t broken, and you can quickly return it to normal.
Related Articles
- The 8 Most Common Problems With Thermostats
- Why Does My Thermostat Change By Itself? (Find Out Now!)
- Honeywell Thermostat Is Blinking A Snowflake? (We Have A Fix)
Nick Durante
Nick Durante is a professional writer with a primary focus on home improvement. When he is not writing about home improvement or taking on projects around the house, he likes to read and create art. He is always looking towards the newest trends in home improvement.
Recently Published
What Kind Of Caulk Is Best For The Kitchen Sink?
There is no reason to skimp on materials when it comes to plumbing fixtures. This is especially true for kitchen sinks because they are essential to everyday life and every component is important....
Continue Reading
What Kind Of Tile Is Best For Shower Walls?
Choosing the right tile for your shower can be quite difficult. The tile that you choose ultimately determines how your shower will look and how easy it will be to clean and maintain. So, what kind...
Continue Reading
FAQs
Thermostat Flashing “Cool On” But Not Working? (Possible Causes & Fixes) | Upgraded Home? ›
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.
Why is my thermostat blinking cool on but not running? ›Check the thermostat display for cooling, usually indicated by the words “cool on” or a snowflake icon. If these icons are flashing, the thermostat is in delay mode, which can last up to 5 minutes. This delay protects your equipment from short cycling.
Why does my thermostat say cool on but nothing is happening? ›Clogged air filters are one of the most common reasons a thermostat clicks but AC does not turn on. A filter cleans the air before it circulates throughout your home, trapping dirt particles, dust, and pollen. Over time, these contaminants will clog the filter, limiting airflow to the HVAC system or furnace.
Why won t my AC turn on thermostat flashing cool on? ›If the batteries are dying, your thermostat could be blinking the “Cool On” message. When your thermostat doesn't have enough power, it won't be able to start the cooling or heating process. To properly check your batteries, look for the “Battery Low Indicator” message on the thermostat display.
Why is my AC light blinking but not working? ›One of the most common reasons that AC units show a blinking light is that there are electrical problems. This could be because there is irregular power drawing or loading, and the printed circuit board or electrical wiring is experiencing some issues.
How do I know if my thermostat is malfunctioning? ›- Thermostat Has No Power. ...
- AC or Furnace Won't Turn On. ...
- Heater or AC Won't Turn Off. ...
- Thermostat Doesn't Match Room Temperature. ...
- Thermostat Doesn't Respond. ...
- Short Cycling. ...
- Thermostat Forgets Programmed Settings.
If the thermostat is still unresponsive, make sure the breaker is shut off and remove the cover. If it looks dirty inside, use canned air or a soft artist brush to clean away accumulated grime that may be affecting its functionality. Then look for issues like loose wiring or terminal screws and tighten them up.
Why does my Honeywell say cool on but not working? ›Inspect the Air Filter
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.
If your thermostat has a recessed reset button, press it with a paperclip for 5 seconds and then release. If you have a battery-operated thermostat and reset mode didn't help, try taking out the batteries for 5 seconds and then putting them back in.
Why is my AC cool symbol blinking? ›If the Cool LED indicator light is flashing on the control panel of your window air conditioner, this can be an indication that the evaporator coils are frosting up or are too cold.
Why is my AC light blinking on my thermostat? ›
Why it Happens. If your thermostat keeps blinking during the normal operation of your AC, that usually means there's an issue with the outdoor portion of the system. It's basically been locked out, meaning that it has shut itself down and sent a signal to the thermostat letting it know there's an issue.
Can a bad thermostat cause AC not to cool? ›When your thermostat is working correctly, you can keep it as cool or warm as you need. A bad thermostat can cause your AC to not cool or heat the room to the desired temperature. Air conditioning concerns are more apparent: Your thermostat is one of the best indicators of your air conditioning system's health.
How do you reset the blinking AC light? ›If the unit has developed a fault, as indicated by the indoor green operation light blinking, you'll need to switch off the isolator, leaving it off for 20 seconds or more before turning it back on. This will allow the system to reboot and reset, which should resolve the issue.
Why does my AC have power but won't turn on? ›If your thermostat is off or your thermostat is showing a blank display, try to switch it on. If the thermostat does not turn on, it could also be a case of dead batteries. Be sure to replace the batteries in the thermostat. If your thermostat still won't switch on, it could be a sign that you need a new thermostat.
How do you troubleshoot an AC that won't turn on? ›- 1) Check the Thermostat. ...
- 2) Check the Air Filter. ...
- 3) Check the Circuit Breaker. ...
- 4) Check the Indoor Shutoff Switch. ...
- 5) Check the Outdoor Shutoff Switch. ...
- 6) Identify the AC's Reset Button. ...
- 7) Inspect the AC for Ice Buildup. ...
- 8) Ensure the Condensate Drain Isn't Clogged.
- Faulty Temperature Readings. One of the most obvious signs that your home's thermostat needs replacing is that it has faulty temperature readings. ...
- Display Not Working. Another common indicator is that the display screen isn't working. ...
- AC System Not Turning On.
As with all other systems, your thermostat will eventually become old and outdated. The lifespan of most home thermostats is 10 years. However, you may need to replace yours sooner as newer, more efficient thermostats enter the market.
How do I know if my thermostat fuse is blown? ›A blown fuse inside your thermostat will cause the device to malfunction. You'll need to open the panel and locate the fuse. This is a small, clear cylinder with metal ends and a filament running through the center. If this filament brakes, the fuse has blown and will need replacing.
What causes a home thermostat to fail? ›Power problems are one of the most common causes of thermostat failure. Whether your thermostat is wired to the mains or runs on batteries, a lack of power will stop your thermostat from accepting commands and communicating with your HVAC system.
Why did my thermostat suddenly stop working? ›If your thermostat is blank, the first thing you should do is check the batteries. Chances are, the batteries have died and the thermostat simply can't power on. Replace the batteries and see if your thermostat turns back on. Most thermostats display a low-battery symbol when the juice is running low.
Why is my Honeywell thermostat not turning on the AC? ›
Troubleshooting a Programmable Honeywell Thermostat
Put in new batteries; Check the circuit breaker; Check the indoor unit to make sure all the panel doors are closed; Make sure the power is connected to the furnace or air conditioning unit by checking the switch near the indoor unit is up.
- Power off the thermostat and remove the batteries.
- Put the batteries in the wrong way, with negative to positive and positive to negative.
- Wait ten seconds and put them back in the correct way.
- Your thermostat will be reset to factory settings.
It will turn the thermostat off, and in most cases, it will restore the thermostat to factory settings. If you're experiencing problems with your HVAC system, you should try using the reset button. If that doesn't work, you can always contact an HVAC technician for assistance.
Can resetting thermostat fix AC? ›The most common reason for an AC unit requiring a reset is when the protection circuit breaker in your AC unit kicks in. This typically happens after a power outage and is in place to prevent fires and explosions. A reset can also correct an AC that's only blowing warm air, even when the thermostat is set to “cool.”
Where is the reset button on my home AC? ›Look for it first around on the exterior of your machine, especially along the bottom edge near the ground. An AC's reset button is typically red and visible, so it should be easy to spot. If you don't see a reset button on the outside, it could be located inside the unit behind the service panel.
What happens when AC thermostat goes bad? ›If the thermostat goes bad, it can cause the HVAC system to switch on and off irregularly. This results in places closer to the HVAC system getting more cool/hot air, with rooms furthest away getting barely any. The Interface Won't Respond.
Why is my thermostat in delay mode? ›Each thermostat model has a different display message when a delay occurs. This delay can be up to five minutes under normal operating conditions. A delay is used to protect your heating and cooling equipment from coming on too quickly (known as short cycling), which can cause damage.
How do you fix a flashing snowflake on a thermostat? ›If your Honeywell thermostat has a blinking snowflake it means your system is in delay mode. Give it five minutes and it should cycle on again.
How do you clean an AC thermostat sensor? ›Using a clean, soft paintbrush and a gentle touch, dust the inner workings of the thermostat. For grime or debris at points where the electronic components touch, slide an open dollar bill like dental floss between them to loosen and remove it. An alternative tool is compressed air.
How often do you charge Freon? ›Most carmakers recommend that you recharge your air conditioning system every two years. But many factors can affect how often you need to recharge your system, including the climate you live in and how frequently you use your AC.
Do all thermostats have batteries? ›
Batteries Not Included
Many thermostats still use batteries, while others draw power from your home's electrical or HVAC system. The typical battery-powered dial, switch, digital or programmable thermostat is going to take regular AA or AAA alkaline batteries, a button-style 3V lithium battery or a 9-volt battery.
How Do You Know If a Thermostat Is Broken? The heating, ventilation, and air conditioning (HVAC) system in your home is controlled by your thermostat. If your thermostat isn't working, your furnace, whole-house fan, and AC unit are probably not functioning correctly, either.
Why is my home air conditioner turning on but not cooling? ›If your air conditioner is running, but not lowering temperatures inside, one issue could be a blocked or clogged condenser coil. When operating correctly, the condenser fan draws air into the outdoor unit through the condenser coil to pull heat energy out of your home.
Why won't my AC turn on in my house? ›Check your breaker box for a blown breaker or tripped fuse. You may be able to fix this AC issue with the flip of a switch. If that doesn't do the trick, check the wiring in your thermostat. A loose or frayed wire could also prevent your unit from turning on.
How long does it take for a thermostat to reset? ›Reset the Thermostat
Common methods for resetting a thermostat include installing the battery backward for five seconds, pushing a recessed reset button with a pin or paper clip, or shutting off the breaker to the thermostat for 30 seconds.
Installing a new AC capacitor usually costs between $80 and $400, including labor, but most homeowners pay around $190. Several factors can affect these costs. For instance, if you live in a particularly hot region with a high demand for AC technicians, you'll likely pay more in labor than in cooler regions.
Why is my AC in delay mode? ›Each thermostat model has a different display message when a delay occurs. This delay can be up to five minutes under normal operating conditions. A delay is used to protect your heating and cooling equipment from coming on too quickly (known as short cycling), which can cause damage.
How do I reset my thermostat? ›Reset the Thermostat
Common methods for resetting a thermostat include installing the battery backward for five seconds, pushing a recessed reset button with a pin or paper clip, or shutting off the breaker to the thermostat for 30 seconds.
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.
How do I get my AC to kick on? ›- Check the Thermostat. It should be set to cool. ...
- Look for a Tripped Breaker. ...
- Change the Air Filter. ...
- Check the Shut-off Switch.
- Check the Inside Shut-off Switch. ...
- Make Sure the Condensate Line Is Clear. ...
- Try the Reset Button.
Is it bad for AC to run nonstop? ›
The constant running will reduce pressure in the cooling coil until it freezes over, which is dangerous as it can cause liquid refrigerant to flood back to the compressor and damage it (the compressor is a very expensive part).
Why is my air conditioner not getting down to set temp? ›If your air conditioner is running, but not lowering temperatures inside, one issue could be a blocked or clogged condenser coil. When operating correctly, the condenser fan draws air into the outdoor unit through the condenser coil to pull heat energy out of your home.
How do I know if I need to reset my thermostat? ›If you've been cranking the thermostat up and down, but failing to achieve a comfortable temperature, you may need to reset the thermostat for your heating and cooling system.
How do you reset a thermostat without a reset button? ›Power off the thermostat and remove the batteries. Put the batteries in the wrong way, with negative to positive and positive to negative. Wait ten seconds and put them back in the correct way. Your thermostat will be reset to factory settings.