Honeywell Thermostat Not Turning On AC? (How to Troubleshoot)

So your Honeywell thermostat won’t turn on your AC, and you’re not sure how to go about this? We’re here to help!

In this post, we explain the reasons behind this issue and how to fix it yourself. Let’s get started.

Honeywell Thermostat Not Turning On AC

First off, here are some reasons your Honeywell thermostat isn’t turning on your AC:

  • Your Honeywell thermostat is not configured to your cooling system.
  • The thermostat is not set to cooling mode.
  • The RC (Red Cooling) wire is not connected to its terminal.
  • Your furnace is turned off.
  • Your furnace door is open.
  • The batteries in your thermostat are weak.
  • Your air vents are blocked.

With that in mind, let’s look at how to troubleshoot this.

Honeywell Thermostat Not Turning on AC: How to Troubleshoot

So here are some troubleshooting steps to try if your Honeywell thermostat won’t turn on the AC:

1. Configure Your Thermostat to Your AC

Your Honeywell thermostat may not turn on your AC if it is not configured to your heating and cooling systems.

If the thermostat was turning on your AC but suddenly stopped, chances are your HVAC system is no longer compatible with your thermostat settings. Probably because you upgraded your HVAC system.

So, you’ll need to reconfigure your thermostat to your HVAC system to see if it resolves the problem.

Follow these steps to reconfigure your Honeywell thermostat:

  • Press the button below System on your Honeywell thermostat. This will reveal a blank box.
  • Hold the blank box until your Honeywell thermostat’s screen changes and displays your Model ID. Most Honeywell thermostats’ Model ID starts with TH or RH and ends in numbers.
  • Next, tap on the Menu option.
  • Then, select Installer.
  • The system will request you to enter your Date Code. You can find your Honeywell thermostat’s Date Code at the back of the device.
  • If you’ve entered the correct date code, your Honeywell thermostat will display your installation settings.
  • Now, press and hold the UP navigation and FAN buttons.
  • The thermostat will display Function Number 1 and Setting Number 0. Function number 1 refers to the settings for your heating and cooling system types.

Your setting Number is displayed beside the Function Number. There are 5 options for setting numbers in the Honeywell thermostat. You can select any of the options depending on the system in your home:

  • Select 0 if you use an oil, electric, or gas heater with your AC.
  • Select 1 if you have a heat pump.
  • Select 2 if you only use a heater.
  • Select 3 if you use a heater with a fan.
  • Select 4 if you only want the thermostat to operate your cooling systems.
  • Once you’ve chosen the right setting for your AC, click on Done to exit the installation settings.

If this doesn’t help, continue to the next troubleshooting step.

2. Set Your Honeywell Thermostat to Cooling Mode

Is your Honeywell thermostat still not turning on your air conditioner after you’ve configured the device correctly? Then, you might need to check whether your thermostat is set to cooling mode. Your Honeywell thermostat will only be able to switch your AC automatically if its cooling mode is activated.

To determine whether your Honeywell thermostat is set to cool mode, check if its screen displays “COOL ON”. If not, you have to enable cooling mode on the thermostat.

Here’s how to do that:

  • Find the system slider switch labeled Heat Off Cool on your thermostat.
  • Slide the switch to the Cool position
  • Then, use the arrows on the screen to adjust the temperature to your desired point.
  • You have now activated cooling mode on your Honeywell thermostat.

3. Connect your RC Wire to the RC terminal

Your Honeywell thermostat has a wire named RC (Red Cooling), which is located within the thermostat’s body. This wire powers the cooling system in your home (Fan and AC). That said, the RC can only function if it is plugged into the RC terminal.

If your Air Conditioner doesn’t turn on after you’ve switched on your Honeywell thermostat, your RC wire might be disconnected from its terminal. To fix this issue, you have to reconnect your RC wire to the RC system.

You can find the RC wire and terminal by opening the cover of your Honeywell thermostat.

If you’re not sure how to handle wiring issues, get an expert to help you.

4. Turn on Your Furnace

In most homes, the AC and Furnace use the same blower motor. This means that the AC won’t work if the furnace is off.

A blower motor functions by moving hot air from the furnace and AC into the air vents. The air then goes through the air vents into different rooms in the home. Since the blower motor is located within the furnace, cool air would stay in your AC if your furnace is turned off.

Your Honeywell thermostat might have turned on the AC when you switched it on. But you probably think the AC is off because you can’t feel any cool air in the room.

If your Ac doesn’t work after you’ve turned on your Honeywell thermostat, you might need to check whether your furnace is on.

First, ensure that your furnace circuit breaker is on. If you use a gas furnace, its circuit breaker will be single-lever.

On the other hand, electric furnaces often come with double-lever circuit breakers. That said, you may have to switch on several circuit breakers to find the one that works with your furnace. Toggle the lever on your circuit breaker to switch it on/off.

After switching on your furnace’s circuit breaker, you still need to check whether you have turned on your furnace’s switch. Turn on your furnace’s switch if the furnace is still off. You can find your furnace’s switch on a wall beside the furnace.

Lastly, you need to close your furnace door. Most furnaces won’t work if the door is open.

After you close your furnace door, your AC should start working in a few minutes.

5. Clean Your Air Vents

If you still can’t get cool air in your room after turning on your furnace, you might have to clean your air vents. Your air vents circulate air from your AC and heater to the rooms in your house. But air may not pass through the vents if they are blocked.

Air vents get blocked when dirt accumulates on their surfaces. Cleaning your air vents will let air circulate through all the rooms in your house. You can clean your air vents by washing their covers with soap and water.

6. Replace the Batteries

If your Honeywell thermostat’s battery is low, it may not turn on your AC. So, you’ll need to replace the batteries.

You can check the status of your Honeywell thermostat battery by viewing the screen. If the battery is faulty, the screen will display ‘No power source’. If you see this message on your screen, it’s time to change your Honeywell thermostat battery.

Follow these steps to replace your thermostat’s battery:

  • Remove your thermostat from the wall.
  • Open the compartment on the side of your thermostat to remove the batteries.
  • Take out the old batteries and place new ones in the compartment.
  • Now, close the compartment and remount your Honeywell thermostat on the wall.

7. Reset Your Honeywell Thermostat

If your AC still doesn’t work after you’ve tried all the troubleshooting methods above, reset your thermostat. Your resetting method may differ based on your thermostat’s model ID.

To determine your thermostat’s Model ID, remove it from the wall and look at its back. Your Model ID is the numbers that follow the letters RHT, CT, TH, RLV, TL, CT, or T. Now that you have confirmed your thermostat’s model ID, you can start resetting it.

Here are the different ways to reset each Honeywell thermostat model:

Honeywell 6000 series:

  • Turn your thermostat on.
  • Press the button below Fan and the Up arrow button simultaneously.
  • Hold both buttons for about 5 seconds. Then, release them.
  • Next, press and hold the button on the bottom left of your Honeywell thermostat.
  • Keep holding the button until the screen displays the number ‘39’.
  • Tap on the Down arrow and hold it until you see ‘0’ on the screen.
  • Now, click on Done to complete the reset.

Honeywell 7000 series:

  • Turn off your Honeywell thermostat and unplug it from the wall.
  • Unmount the thermostat from its mounting plate.
  • Open the side compartment in the thermostat to reveal its batteries.
  • Remove the batteries, turn them the wrong way and insert them into the compartment.
  • Wait for about 5 seconds.
  • Open the side compartment again and insert them in the correct manner.
  • Your thermostat’s screen should come on now.
  • Place your thermostat back on its mounting plate and restore power to the device.
  • You have reset your Honeywell 7000 series thermostat.

If none of these reset methods work for you, refer to your user manual or try googling your thermostat’s model to find the reset instructions.

Wrapping Up

So that’s how to troubleshoot a Honeywell thermostat that won’t turn on AC. If the problem persists after trying all the troubleshooting steps in this post, try contacting Honeywell support for help or get an HVAC expert to help you check the thermostat.

You may also like to see how to troubleshoot heating issues in a Honeywell thermostat, Braeburn, and Vivint thermostat.