If the “Cool On” or “Heat On” message is flashing on your thermostat and the system is not getting to the set temperature, you obviously have a problem.
Normally these messages only flash for five minutes and then turn solid to indicate the system has started. However, if it keeps flashing, then make sure to follow my troubleshooting steps below to get to the root of the problem.
At SmartHomePerfected we always advise readers not to undertake any work they are not competent in performing and if, in any doubt, it is best to seek the assistance of a professional.
What Does the “Cool On” or “Heat On” Indicator Mean?
During normal operation, the “Cool On” or “Heat On” message stays lit depending on the temperature mode.
So if the AC is working to cool down the house, the thermostat will say “Cool On.” Meanwhile, if the heat pump is working to heat up, the thermostat will instead display “Heat On.”
Compressor Protection Feature
However, if either of these messages are flashing it can imply that the thermostat is running the compressor protection feature. In some models, this message is displayed as “Waiting for equipment”.
As the name suggests, it's an intentional safety feature to prevent any harm to your compressor, especially in the event of a power outage.
By taking about 5 minutes to cycle, the thermostat ensures that everything runs smoothly and avoids the damage caused by intermittent power cuts or surges.
So after you’ve just recovered from a power cut, the “Cool On” or “Heat On” message would stay flashing for five minutes. After which, it will remain solid and the HVAC system will kick in.
10 Steps to Troubleshoot a Blinking “Cool On” or “Heat On” Indicator
When the “Cool On” or “Heat On” indicator continues to flash for more than five minutes without hot/cold air coming in, it can indicate an issue with the HVAC system.
If so, I recommend following the troubleshooting steps laid out below.
1. Wait 5-10 minutes
Your thermostat could be facing a slight delay in restarting and activating its compressor protection feature.
Make sure to wait at least 5 minutes before further troubleshooting. I recommend waiting for a solid 10 minutes so you can confidently rule out the compressor protection feature.
2. Set the Thermostat to its Lowest Temperature Setting
You can verify the thermostat's ability to manage the cooling system by adjusting its settings.
- First, set the thermostat to the lowest possible temperature.
- Ensure that the mode is set to “Cool” and that the fan setting is on “Auto.”
- After making these adjustments, give it some time.
- Check if the AC comes to life or if you experience any change in the room's temperature.
This will help determine if the thermostat is effectively controlling the temperature function.
3: Check if the Thermostat is in Setup Mode or if the Clock is Set
In certain models, when the thermostat is recovering from a power outage, it may revert to setup mode, causing the “Cool On” lights to blink.
To resolve this, check your thermostat's settings and make any necessary adjustments.
Also, verify that the time displayed on your thermostat is accurate. An incorrect time setting can interfere with the schedule settings and glitch out the thermostat.
4: Check the Thermostat Batteries/Power Connection
Weak batteries can prevent your thermostat from initiating the cooling process.
To fix this, replace the thermostat batteries by removing the thermostat from the wall mount and replacing the batteries on the back of the panel.
If your thermostat uses a 24 VAC power source instead of batteries, inspect the wiring.
To do so:
- First, turn off the power to your HVAC system.
- Next, remove the thermostat, ensuring you unscrew it first if necessary.
- Then, examine the C-wire to confirm its proper connection.
- Make sure there is no dust, dirt, or debris, and clean the contacts.
- You can also try reconnecting the terminals, making sure they are secure.
Check out our guide on how to change Honeywell thermostat batteries
5. Check the Voltage at the Thermostat Contacts
If you know how to troubleshoot electrical components and you already have a multimeter, you can check the voltage in the thermostat wires.
Make sure that the R and C contacts have a voltage between 24-30V; lower values might indicate insufficient power.
6. Check the Power in Each Component of the HVAC System
If the previous steps haven't resolved the issue, you'll need to diagnose the rest of the HVAC system.
- First, inspect the power supply of your air handler, fans, furnace, and AC unit.
- Watch out for unusual humming or clicking noises coming from your equipment, as these might indicate a problem.
- Also, examine the power supply for each device.
- Make sure that connectors and sockets are appropriately plugged in, and switches are turned on.
- While examining your equipment, check if the doors or panels are properly closed. Loose or detached parts and any obstructions may cause the safety switches to disconnect, especially the furnace door.
- If possible, check the fuses or switches visually or by using the continuity setting on a multimeter
- Then, inspect your circuit breakers for any irregularities.
- Try turning your equipment on and off, as well as resetting the breaker corresponding to these devices.
7. Check the Indoor AC Filter
It's essential to regularly inspect your indoor AC filter to make sure it doesn’t need replacing.
- A clogged or dirty filter hinders proper airflow and can lead to decreased cooling efficiency and poor air quality inside your house.
- It can also put extra strain on your thermostat and other equipment, ultimately leading to higher energy bills.
- So I recommend making it a habit to change your AC filter every three months or as recommended by the manufacturer.
8. Check AC Coils and See if they are Dirty
The external AC coils can also become dirty or blocked over time.
- As the coil accumulates dirt, it hampers proper airflow and reduces its ability to absorb heat and adequately cool the air.
- Inspect your AC unit's coils to see if there is buildup on the fins, indicating the need for a thorough cleaning.
- However, always make sure the unit is turned off before attempting any cleaning or maintenance.
- To reduce the chances of clogging and improve efficiency, keep the area around the AC clean and provide ample space for airflow by removing any nearby plants or debris.
9. Reset your Thermostat
In some cases, resetting your thermostat to factory defaults might be necessary.
Keep in mind that this process will erase your settings and programmed schedule, so it's a good idea to take note of any configurations you don't want to forget.
To reset a Honeywell thermostat, check out my detailed reset guide which covers all Honeywell thermostat models.
10. Bypass the Thermostat
If you’re somewhat more skilled at DIY, especially when it comes to dealing with electrical components, you can try to bypass the thermostat.
However, make sure you have a multimeter and a proper tool to create a jumper wire.
- First, turn off the power switch on the furnace or air handler, and also disconnect the thermostat from the breaker.
- Then, take out the thermostat from the wall mount.
- After that, run one end of a jumper to R (Power) and the other end to Y (Cooling) or W (Heating) on the thermostat contacts.
- With this setup in place, turn the power back on and check if the AC or furnace/air handler turns on.
- If these components turn on without any issue, the thermostat is indeed defective.
Final Step: Call in the Professionals!
When you've exhausted all possible solutions and your thermostat is still flashing “Cool On,” it's time to get the help of professionals.
- A trained technician can likely pinpoint the problem and fix it with ease.
- Some common issues that may require professional intervention include damaged wiring, a malfunctioning capacitor, obstructed sensor, or a blown fuse.
- In addition, components like the compressor, condenser, or fan motor may need further inspection.
- For a recently installed thermostat, an expert can verify proper wire connections and ensure the device is set up correctly for your specific HVAC system.
If the Cool On or Heat On message is flashing for more than five minutes, it will require you to troubleshoot the entire HVAC system.
The troubleshooting guide above will help you do just that so if you follow those steps, you’ll be able to get to the root cause in no time.
However, if you aren’t able to check the circuit breakers or the rest of your HVAC system, always get a professional to help you.