nest thermostat blowing hot air on cool

Is your Nest Thermostat blowing hot air on cool mode? Isn’t it just annoying that it’s not able to give us the temperature we want to have?

We can all relate to the feeling of disappointment, but can we fix this without a professional?

In this guide, we will be going through the reasons why your Nest Thermostat is not blowing cold air even if it’s set on cool. Furthermore, we’ll walk you through the steps you can do to troubleshoot it!

If your Nest Thermostat is blowing hot air in cool mode, it may be due to a heat pump, loose wires, and cables or incorrect O/B wire settings.

Then, if necessary, perform a check if it’s fully compatible or if it needs professional maintenance.

Right before jumping into the guide, let us first try to unravel some of the reasons why your Nest Thermostat is not blowing cold air.

Possible Causes of Your Nest Thermostat Not Blowing Cold Air

As easy as we want this to be, there isn’t a single reason why this happens. Most of the time, there’s just one culprit.

However, there are instances where you’ll see and notice that this dilemma is caused by multiple issues running at the same time.

Nevertheless, here are some of the common and most possible causes why your Nest Thermostat is blowing heat instead of cool air.

  • Thermostat wires aren’t inserted properly
  • Your device might not be compatible with the device
  • You have a heat pump
  • Different O/B wire settings
  • Your system needs maintenance

I know, it’s a lot to take in, but we promise you that we’ll guide you through this easily and conveniently.

So, would you be able to fix and resolve this by yourself? Or would contacting a professional be better and a lot faster?

Fixing the Nest Thermostat Blowing Hot Air on Cool Problem

fix nest thermostat blowing hot air on cool

Before contacting someone, you can try out this process first!

You can actually save time, money, and it might not actually be as complicated and as difficult as it seems!

So, without further ado, here are the steps on troubleshooting your Nest Thermostat blowing hot air on cool and vice versa!

1. If You’re Using a Heat Pump

This method is for users who utilize a heat pump rather than the conventional HVAC system where a furnace is used.

Step #1: Check the Nest’s Wires and Cables

The first step you want to take is to check the wires and cables of the Nest device. You can find them by dismantling and dismounting their front and outer cover.

Ensure that all wires are inserted correctly and perfectly.

Step #2: Are You Sure That You’re Using a Heat Pump?

Check and see if you’re really using a heat pump. To find this out, you do the following:

  1. Set your Nest Thermostat to heat mode.
  2. If warm air is coming out of the vents, check the unit outside your home.
  3. If it’s running, then you most certainly have a heat pump.

Note: Heat pumps are usually seen outside of the establishment where the HVAC is installed.

Step #3: Test Your Nest Thermostat

The next thing you want to do is to test and observe your Nest Thermostat. Here’s how you can do that.

  1. Set your Nest Thermostat to heat mode.
  2. Raise and increase the temperature until you see the thermostat sensor turn orange.
  3. Then, wait for a few minutes and feel the air coming out of the vents.
  4. When it’s working fine, invert the process and set the thermostat into cool mode.

Step #4: Modify the O/B Wire Settings

Changing or modifying the O/B wire settings if you’re using the regular Nest Thermostat is simply factory resetting it.

To factory reset your Nest Thermostat, what you have to do is to go to your Nest Thermostat and navigate to Settings > Factory Reset, then wait for it to be reset to default.

Then, initiate the setup of the thermostat again using the Google Home app.

Step #5: Check and Test the O/B Wires

You should only be using O/B wires if you’re using a heat pump. Otherwise, there shouldn’t be any wires in the O/B connector.

To check this, turn off the power from your HVAC system, then remove the O/B connector. Ensure that the wires aren’t corroded and if it is, clip and strip the wire to unveil the copper inside it.

Make sure that you put the wire back properly into the O/B connector.

That’s it! By now, your thermostat should be working perfectly again!

2. If You’re Using a Conventional System (Furnace)

Should you not be using a heat pump, here’s the process of how you can put an end to this dilemma.

Step #1: Check All Thermostat Wires

The first step is to ensure that all wires are inserted and connected properly in the thermostat. Before doing this, make sure that the system is fully powered off.

Detach and reattach the thermostat wires to their respective designations.

Step #2: Check If Your System Needs Maintenance

Just like any other system, your HVAC system would need maintenance, too. Here are a few signs and symptoms that your system is yearning for professional maintenance:

The first is when your system works normally for a time. But, it goes back to having problems, especially after you restart it.

The last would be when the screen of your Nest Thermostat turns blue if you want to cool and orange if you want to heat – but it’s not turning on.

For better and more efficient care, contact an expert or a professional to help you with it.

Step #3: Is Your HVAC System Compatible?

Most 24V HVAC systems work in compatibility with Nest Thermostats. However, several systems aren’t just compatibility-friendly compared to other systems.

In these instances, you may need a C (common) wire for it to be compatible.

Step #4: Try a C Wire or the Nest Power Connector

A C-wire or a common wire is a wire that helps WiFi thermostats get continuous power.

Meddling with C wires requires skill and experience. So, if you’re not too sure about how to use one, you can use the Nest Power Connector instead.

This is a simple device that you just need to plug near your Nest Thermostat. The Nest Power Connector can serve as the external C wire of your entire HVAC system.

Step #5: Contact an Expert

If all of these still didn’t work, then, the next best thing is to contact an HVAC professional to help you with it.

There are a few things that you can do by yourself, which won’t involve any technicality, but if it’s still not working, the next best thing to do is to contact a professional.

When you finish this process, your Nest Thermostat should be functioning back again properly in no time!

My Nest Thermostat is Still Not Working Properly, What Should I Do?

In the event that the problem still persists even after you’ve done the steps, the best way to go is to contact a professional HVAC specialist about it.

Whether or not you have experience, you may not have the proper tools to successfully resolve this issue.

To fix your dilemma of your Nest Thermostat blowing hot air instead of cool and vice versa, check the wires and cables of the thermostat, modify the O/B wire settings if necessary, and check if it needs professional maintenance.

You can also make use of a C-wire or a Nest Power Connector, too!

Read Next: Why is Nest Thermostat Blinking Green?


The next time that you notice your Nest Thermostat blowing hot air on cool, you can go back to this guide and fix it without breaking a sweat.

Don’t worry, this guide does not require you to be an expert in HVAC systems!

Nicole B