How to fix Nest Thermostat compressor not turning on? Practical Fixes (2023)


Google Nest Thermostat is one of the most popular and user-friendly Smart Thermostats of 2023.  

The thermostat has great smart features that efficiently control both heating and cooling of your home. However, sometimes the Nest thermostat won’t turn on your AC compressor, which can be truly problematic, especially when it’s hot and humid.  

A Neighbor of mine has the Nest thermostat installed in his home. He was having the same AC compressor issue, due to which his Nest was not cooling to set temperature!  

He knows I am an expert in smart home devices, so he asked me how to fix it. We tried a number of fixes, and thankfully I was able to make his thermostat and HVAC system up and running.  

In today’s article, I will provide you with all possible causes and the fixes that I tried. You can implement them to fix the Nest Thermostat compressor not turning on issue!  

Possible causes of Nest Thermostat not turning on AC Compressor 

 Nest Thermostat compressor not turning on - All possible causes

Your Nest thermostat won’t turn on AC compressor due to a number of reasons. The possible causes can be insufficient power supply, tripped breakers, a bad start capacitor of the AC, a nearly low thermostat battery, incorrect thermostat settings, Wi-Fi or internet problems or simply the Nest thermostat requires a reset! 


Nest thermostat compressor not turning on – How to diagnose and Fix? 

Now that we know the possible causes, let’s diagnose them and try to fix them one by one. Let’s begin with the simpler ones first.  

Diagnosis and Fix 1: Check Nest thermostat’s settings  

Nest Thermostat compressor not turning on - Check Thermostat Settings

The very first thing to check is whether your Nest thermostat is set to ‘cooling’ mode.  

It’s obvious that if it’s not set to cooling, the AC will never turn on. Do ensure that the cooling is on! 

The next very important thing you need to ensure is that your Nest thermostat’s temperature is set lower than your home’s room temperature.   

This makes sure that the Nest thermostat commands the AC to turn on as you need a cooler temperature than your existing temperature.  


Diagnosis and Fix 2: Check if the Nest thermostat battery is low or near to low 

Nest Thermostat compressor not turning on - Check for Low Thermostat Battery

The next quick thing you should check is whether the Nest thermostat’s battery is low. You can check it inside the Google Home or Nest app.  

If the battery is low or close to low, consider changing the Nest thermostat’s battery.  

If the battery is not low or even close to low, you can ignore this step and move on to the next fix.  


Diagnosis and Fix 3: Ensure that there are no Wifi router or internet related issues

 Nest Thermostat compressor not turning on Check for Wifi router or Internet issues

This is a very common problem that nearly all IoT devices encounter at some point in time. Moreover, the Nest thermostat also encounters many errors due to unstable internet.  

The Nest thermostat needs a stable internet connection. You can do a speed test to ensure that your Internet is stable.  

Moreover, make sure that your thermostat is receiving strong Wi-Fi signals. If not, try moving your router closer to the Nest thermostat.  

Finally, you need to check whether your Nest thermostat is having an issue connecting to your Wi-Fi router.  

If so, you can restart the router. If that doesn’t work and the thermostat is still unable to connect to the router, grab a pin/paperclip, insert it into the hole labelled ‘Reset’ on the back side of your router, and reset your Wifi router.  


Diagnosis and Fix 4: Check if the Outdoor unit (HVAC) is getting enough power  

 Nest Thermostat compressor not turning on Check if the Outdoor unit is getting enough power

If the battery is good, and the Nest thermostat is set to cooling, there is a huge probability that your outdoor unit is not getting enough power.  

This could be caused by number of reasons, so let’s check each cause one by one 


Fix 3.1: Check for Tripped Circuit breakers of the HVAC 

Nest Thermostat compressor not turning on Check for Tripped Circuit breakers

Circuit breakers control the power supply of the HVAC system. The breakers usually trip due to voltage fluctuation or sometimes due to a short circuit (to prevent hazards). 

You can check the breakers if they have tripped. If so, try resetting them. If they keep tripping again and again, you should call a technician to look into this issue.   


Fix 3.2: Check for a bad start capacitor 

Nest Thermostat compressor not turning on Check for a Bad Start Capacitor

Bad Capacitors are one of the major culprits of such power related issues.  

In order to spot whether the capacitor has gone dead or not, you should make a physical analysis. Dead capacitors are usually swollen (just like when a battery has gone bad).  

If this is so, you need to replace it with a new capacitor. You can get it from the market or make an online purchase.  


Diagnosis and Fix 5: Factory reset your Nest Thermostat 

Nest Thermostat compressor not turning on Factory Reset Nest Thermostat 

If nothing works and your Nest thermostat is still not turning on the AC compressor, as a last resort, you will need to factory reset your Nest thermostat.  

This is the last option, so it must only be carried out if no other fix works.  

How to Reset Nest thermostat? 

In order to reset your Nest thermostat, follow these steps: 

  1. Open “Settings” from the Menu of your Nest thermostat. 
  1. Confirm the prompt; Select “Yes” 
  1. The factory reset will start now.  

This will remove all settings including saved Wi-Fi passwords and your personal settings. You will need to set up your Nest thermostat again, but hopefully this time around, you will get rid of the Nest Thermostat compressor not turning on issue!  


Summing it up 

Smart Home Devices have certainly enhanced our lifestyles and provided us ease. However, sometimes these smart devices are a cause of frustration when errors like these occur.  

If an error occurs, that doesn’t mean it is unfixable! Such is the case with the Nest thermostat compressor not turning on issue!  

In this article, I provided you with all the practical fixes that I myself tried to fix this issue. I hope it was useful for you!  

Happy Smart Homing! 

Some Related Questions (FAQs) 

 Here are some common questions related to the Nest thermostat AC and AC compressor. 

Why is Nest fan not turning on with AC? 

The major cause of Nest fan not turning on with AC is lack of power! The Nest thermostat might not be getting suffiecient power due to loose wiring. Check for loose  

If your Nest fan does not turn on with your AC, the first thing you need to check is loose wiring. You want to make sure that the wires in your Nest thermostat are connected to the right terminals (as labelled). Particularly examine the C wire to make sure that it is firmly set in its slot (does not have a lose connection). 

Moreover, do also check that the Nest thermostat’s battery is low or not. Although battery is used as a backup in Nest, a low battery can cause insufficient power and disrupt functionality of the Nest thermostat.  


Why is Nest fan not turning on with heat? 

This can be caused by incorrect settings in the Nest thermostat. Go to Settings of the Nest thermostat, then Equipment, then keep going forward until you see Pro Setup. Select it, and from there, select your W wire to set the fan to activate heat. 

Stefen Turner

Hey! My name is Stefen and I am the founder of Smart Home Hunt. Prior to starting this blog, I used to work as a Full-Stack Web Developer in the field of Internet of Things (IoT).