Nest learning thermostat cooling way beyond normal margins

[A_lec]

My nest learning thermostat has suddenly started cooling well beyond the set temperature. It is causing my house to feel like a refrigerator, and I have to constantly intervene with its functioning throughout the day and night.

I have a Google Nest learning thermostat 3rd generation, and 3 Google Nest temperature sensors placed at specific locations in my house. I have the learning option turned off, and a schedule set to read the different sensors at different points in the day. This has worked fine for several months, but suddenly over the last few days the system will keep cooling to several degrees below the set temperature, and I have to switch to a different sensor to basically resest the thermostat so it understands it has cooled beyond the set temperature and then will turn off. I have had it set to 73 and it was still cooling even though the sensor it was assigned to was reading 70.

The thermostat is several years old, and the sensors are a few months old. I have checked the connection on all sensors, they are all connected and the temperature readings update just fine. The HVAC cooling system works fine and was cleaned this spring.

How can I fix this issue? I know it's not normal behavior because I've had the thermostat for years, and the sensors worked perfectly for regulating the temperature up until a few days ago. The temperature outside did not dramatically change over the last few days either. 

[chaconmorales]

Hi A_lec,

Thanks for reaching out to the Community. I am sorry that you are having issues with your Thermostat cooling mode, I’d be happy to help you. Let’s check it out.

A Nest Learning Thermostat cooling excessively can be uncomfortable and lead to higher energy bills. Since you've already tried the basic troubleshooting steps and before we get started with further details, let me ask you some important questions:

• Does the thermostat display show any error codes or messages?
• Are you able to share a picture of your wiring?
• Have you reviewed the temperature schedule for your thermostat?
• What type of system do you have? (Heat Pump or conventional type)

Here are some steps you can try to troubleshoot the issue:

1. Check the Nest App and Thermostat Settings:

• Thermostat: Verify that your thermostat is set to "cool" mode and the desired cooling temperature is lower than the current room temperature. You can check the following guide to Troubleshoot strange heating or cooling behavior.
• Schedule Verification: Review your Nest's cooling schedule in the app. An unexpected change in the programmed schedule might be causing the continuous cooling.
• Auto Away Feature: Verify if the "Auto Away" feature is enabled. If active, and you're home, it might be interpreting your absence and over-cooling the house. Disable "Auto Away" if you're present.

2. Heating and Cooling System:

• Air Filter Check: I understand that your system recently received maintenance, but a clogged air filter can restrict airflow and reduce the efficiency of your HVAC system. Replace the air filter with a clean one according to the manufacturer's recommendations.
• Frozen Coil (Less Likely): In rare cases, the evaporator coil in your air conditioning system might be frozen due to excessive cooling. If you suspect a frozen coil, turn off your air conditioner and consult an HVAC professional for inspection and repair.

You can also check the following article to Troubleshoot issues with the Nest Temperature Sensor.

Let me know how it goes. 

Best regards,

Mario