Nest Thermostat Not Turning On AC [Quick Ways to Fix]

Your Nest thermostat used to work perfectly, but now it won’t turn on your AC.

If that sounds like you, keep reading to see how you can troubleshoot this issue.

But first, you want to know why this is happening. If your Nest thermostat won’t turn on the AC, here are some reasons behind this issue:

Your thermostat wires are loose or inserted incorrectly.
The battery in your Nest thermostat has almost reached the end of its lifespan.
Your Wi-Fi router is too far away from the thermostat.
The thermostat is dusty.
Your HVAC is running non-stop.
Your Nest thermostat accidentally tripped off.
Power outage

Now, let’s see how we can fix these problems.

Table of Contents

Insert Your Nest Thermostat Wires in the Correct Terminals

You probably know that your Nest thermostat has several wires hidden within its body. Each wire needs to be inserted into its appropriate terminals for the thermostat to function properly.

So, if your Nest thermostat won’t turn on your AC, the wires might have loosened or inserted incorrectly.

Out of all the wires in the Nest thermostat, the RC (Red Cooling) wire is critical to your AC’s operation. So, if your AC isn’t turning on, it’s probably because there’s an issue with the RC wire (loosened, burned, or inserted in the wrong terminal).

To resolve this issue, remove your thermostat from the wall and inspect the wires. Ensure all wires are inserted in the right terminals.

If you’re not sure how to check and fix the wires in your thermostat, get an expert to help you with that.

Replace/Charge Your Nest Thermostat Battery

Your Nest thermostat may fail to switch on your AC if its battery is low. The Nest thermostat requires about 3.6 volts to run properly. Originally, your Nest thermostat battery should provide this amount of voltage.

But as your thermostat’s battery gradually reaches the end of its lifespan, the quantity of voltage it offers may reduce. As such, your thermostat may not regulate your AC.

When this happens, you have to charge the battery or get a replacement. See how to charge and fix charging issues in a Nest thermostat.

Move Your Wi-Fi Router Closer to Your Nest Thermostat

Like most thermostats, the Nest thermostat requires an internet connection to control your appliances. If the thermostat disconnects from the internet, it may not be able to turn on your AC.

Your Nest thermostat might lose its internet connection because it is too far away from your router. Moving your router closer to your Nest thermostat should help the device regain its internet connection. Once your thermostat reconnects to the internet, it should switch on your Air Conditioner.

Clean Your Nest Thermostat

If your Nest thermostat is too dusty, it may not turn on your AC. Dust reduces the efficiency of a thermostat. This is probably why your Nest thermostat can’t switch on your AC.

In addition, a dusty thermostat often requires more energy to run than when it is in good condition. The voltage received through your electric supply may become insufficient to run your thermostat. As a result, your thermostat may not operate your AC and heater.

So if you’re having trouble getting your Nest thermostat to turn on your AC, dust might be the culprit. Remove the faceplate of the thermostat, then use a soft brush and gently wipe the dust from the thermostat.

Regulate the Operation of Your HVAC

Is your HVAC (Heat, Ventilation, Air Conditioning) running too frequently? Then, it may be the reason your Nest thermostat can’t turn on your AC. If your HVAC runs continuously, it may prevent your thermostat from reading the room temperature correctly.

For instance, if the cooling system in your HVAC runs continuously, your Nest thermostat may confuse the room temperature for cold when the weather is actually hot. So, the thermostat may turn on the heater instead of the AC.

If you want your thermostat to power up your AC, don’t keep your HVAC on throughout the day. Instead, leave the thermostat to control the operation of your heating and cooling systems.

You can do this by setting all the systems in your HVAC to Auto. This includes your fan, AC, heater, and boiler. When you activate this setting, your HVAC will only come on when the temperature in your home rises or falls below your desired temperature.

Turn On Your Nest Thermostat’s Circuit Breaker

Sometimes, your Nest thermostat’s circuit breaker may accidentally trip. This will cut off power from your Nest thermostat. Perhaps you weren’t looking at your thermostat when the circuit breaker tripped. So, you might think that your Nest thermostat is on when it has gone off.

If your AC hasn’t turned on several minutes after you’ve switched on your thermostat, check whether the thermostat is still on. If not, go to your electric panel and switch on your Nest thermostat’s circuit breaker.

Reboot Your Nest Thermostat

Did you recently experience a power outage in your home? Then, you might need to check whether your Nest thermostat still gets its required voltage. Your Nest thermostat needs a minimal amount of 3.6 volts to function effectively. If the voltage in your Nest thermostat is lower than 3.6V, you might need to reboot your Nest thermostat.

To find the voltage quantity in your Nest thermostat, here’s what to do:

Click on Settings on the thermostat’s display.
Then, tap on Device Information.
Next, select Power. Under the Power section, choose Battery Label. You’ll find the voltage quantity.

Is the voltage quantity on your Nest thermostat below 3.6 volts? If yes, follow these steps to reboot your Nest thermostat:

Press and hold your Nest thermostat’s ring for about 10 seconds. Release the ring once the screen goes off.
Press the ring again to switch on your thermostat. Remove your finger from the thermostat’s ring when the screen turns on. The Nest logo will appear to show that your Nest thermostat is restarting.
You have rebooted your thermostat.

Now check to see if the problem is resolved. If not, try turning on AC on your Nest thermostat.

Before switching on your AC from your Nest thermostat, you need to activate cooling mode on your Nest app.

The following steps will show you how to do this:

Open your Nest app on your phone and click on the Nest thermostat button from the home screen. The Nest thermostat button is the button that displays your thermostat’s current temperature.
Next, click on Heat in the bottom left part of the screen.
The system will now display a pop-up with a list of options like Heat, Heat-Cool & Cool.
Choose Cool to set your Nest thermostat to cooling mode. When you activate the cooling mode, your thermostat’s temperature might increase.
Move the cursor on the temperature tab to reduce the temperature to your desired point.
Now, exit your Nest app.

Since you’ve already turned on cooling mode on your Nest app, you can now switch on your air conditioner from your thermostat.

Follow this guide to turn on your Air Conditioner from your Nest thermostat:

Press your thermostat’s ring to reveal the Main Menu.
Turn the wheel on the ring to the thermostat icon.
Then, push on the icon to select it.
You’ll see a list of options like Cool, Heat, and Heat-Cool, just like in the Nest app.
Scroll the wheel again to select Cool.

Your AC should start working now.

Closing Thoughts

So that’s how to troubleshoot your Nest thermostat—if it’s not turning on the AC. You want to try all the troubleshooting steps until the issue is resolved.

If your thermostat still can’t turn on your AC after you’ve attempted all the troubleshooting methods in this post, contact Nest Support for help. You may also consider getting an HVAC professional to check your thermostat and HVAC system.

You may also like to see how to troubleshoot AC problems in Honeywell and Luxpro thermostats.