Thermostat Set to Cool But Heating? Fix in Minutes!

Is your thermostat set to cool but heating? Getting this issue can get frustrating. The good news is that we have the solution you’re looking for!

If you’ve just started to get this problem, you know something is wrong with your thermostat.

You want to confirm that your thermostat is cooling by checking the display for any icon that indicates it.

To fix your thermostat blowing hot air even though it’s set to cool, you want to make sure that it’s set to cool mode. Change the mode on the device or app that controls your thermostat. Checking the R, Rc, O, and B wires is also something you need to do as these control heating and cooling.

Now that you understand this particular issue with your thermostat, let’s look at the problem’s origins. We can then move to the troubleshooting guide to resolve it.

Why Heat Comes On When Set to Cool on My Thermostat

If you’re experiencing this error where the heat comes on even though your thermostat is set to cool, you want to check where this issue is coming from.

We recommend checking your thermostat’s settings, then looking at the wiring as you’ll discover those are set incorrectly.

Here are the problems that could cause this particular error with your thermostat and HVAC system:

1. Malfunctioning Thermostat

An issue with your thermostat’s functions can cause problems with heating or cooling. It can do the opposite of your current settings.

2. Dirty Thermostat or Condenser

Having this problem can affect the cooling potential of your thermostat and HVAC.

It can work as hard as it can to cool your home, but if the condensers are dirty and clogged, they can’t dissipate the heat properly.

3. HVAC System, not the Right Size

If your AC is too small for your home, it will have a hard time cooling. It can even fail and not turn on the condenser, blowing hot air.

4. Wrong Wiring Configuration

Several wires connect your thermostat to your HVAC system. Each of them has a specific function. If a couple of them are not in the right place, you will experience this issue.

Now that you understand the possible sources of this issue, we can now proceed to the full fix guide.

You’ll be able to resolve this error in no time by following the steps described!

How to Fix Thermostat Set to Cool But Heating

Before you do anything else like opening up your thermostat, it could be as simple as you may have pushed the cooling button, but it did not switch it to cool mode.

Double-check that your thermostat is set to cool, and you can confirm with icons on display and the app lighting up.

After confirming and you’re certain that it’s set to cool but continues to blow hot air, here are the next steps you can take:

Solution #1: Restart Your Thermostat By Turning Off Your Breakers

If your thermostat fails to switch to cooling mode, the issue is coming from your thermostat’s software.

It could freeze and stop responding to any of your commands. If this happens, your best course of action would be to perform a hard restart of your thermostat.

Here’s how to restart your thermostat by switching off your breakers:

1. Look for your thermostat and HVAC’s circuit breaker switch.
2. Switch it to the OFF position.
3. Wait for 1 to 2 minutes.
4. Turn the breaker switch ON.

Note: After switching on your circuit breaker, we recommend waiting for 30 more minutes before powering up your thermostat.

Solution #2: Clean Your Thermostat and Outdoor Condenser

One of the things you need to look out for if you’re experiencing issues with your thermostat is dust and dirt build-up.

It could disrupt your wiring or condenser coils, preventing your system from successfully switching to cool mode.

Here’s how to clean your thermostat and condenser:

1. Remove your thermostat cover from the wall mount.
2. Use a soft brush to remove the dirt and dust inside your thermostat.
3. Check for corroded wires.
4. Replace the thermostat cover.

Note: To clean the outdoor condenser unit of your HVAC system, you can use a water hose to clean off loose dirt and leaves stuck between the fins.

Solution #3: Recalibrate Your Thermostat

It’s possible that your thermostat is not properly calibrated. If this is the case, your thermostat is cooling properly but not reaching the temperatures that you’re expecting.

Make sure that your thermostat’s settings match the actual temperature.

Here’s how to know if your thermostat is performing as expected:

1. Get a room thermometer.
2. Bring it beside your thermostat.
3. Wait for 10 to 20 minutes.
4. Check if there is a difference between the two temp readings.

Note: You can now change your thermostat’s offset settings so these match. You can also perform a factory reset.

Solution #4: Check Your Thermostat’s R and Rc Wiring

Your thermostat’s R wires are the ones that control your cooling and heating systems.

If this is not connected properly, this is where your system will blow hot air even though it’s set to cool.

Here’s how to check your thermostat’s R wires:

1. Take a picture of your thermostat’s wiring under the front panel.
2. Look at the wiring diagram of your thermostat.
3. Make sure that the R wires are connected to the Rh and Rc terminals.
4. Check if your thermostat brand and model require an R-wire jumper.

Note: Nest thermostats don’t need an R-wire jumper. Amazon Smart Thermostats have built-in jumper switches for the R terminals.

Solution #5: Change Your O and B Wire Settings for Your Heat Pump

If your home is equipped with a heat pump rather than a conventional HVAC system, you will have O and B wires.

These control the valve in your heat pump that switches it from heating to cooling and vice versa.

Here’s how to change the O and B wire settings on your thermostat:

1. Check that the O and B wires are secured to their terminals.
2. Go to your thermostat’s settings.
3. Select the Heat Pump option and find the O/B settings.
4. If O is highlighted, switch it to B.
5. If B is highlighted, change it to O.

Note: There should be no O or B wires under the panel if you have a conventional HVAC system.

Solution #6: Reset Your Thermostat to Factory Settings

If none of these steps resolve your issue, you can bet that resetting your thermostat to factory settings will do the trick. It’s a great way to revert all settings, including recalibrating the sensors.

Here’s how to reset your thermostat to factory settings:

Nest Thermostats:

1. Go to your thermostat’s settings.
2. Turn it to the Reset option, then select it.
3. Choose whether you want to reset all settings or keep some of them.

Amazon Smart Thermostat:

1. Press the Up and Down temperature buttons.
2. Press the Mode button.
3. Hold all three buttons for 10 seconds.
4. Wait until rEs appears on the screen.

Other Thermostats:

1. Turn OFF the thermostat.
2. Remove the batteries.
3. Put the batteries the wrong way.
4. Wait for at least 10 seconds.
5. Reinsert the batteries correctly.

If you’re still experiencing the same issue even after successfully resetting your thermostat, you want to make sure that your system is the right size.

You can call a professional to get an accurate estimate or to help you fix the problem.

Read Next: Amazon Smart Thermostat Won’t Turn On? – (Fixed)

Bottom Line

Now that you have a pretty good idea of fixing your thermostat set to cool but heating, you can take the necessary steps to resolve it.

You will be able to fix it using the troubleshooting steps we described.