11-18-2022 05:42 PM
Help, freezing in my house!
I have a Nest Learning Thermostat. It was an external power supply that is wired to the Common and the Rh ports.
The system is a gas forced air and air conditioning. I do have a transformer on my air handler that supplies power to some of the wires but there was no common which is why I believe the owner who installed this is using an external power supply.
The system stopped working. I pulled the thermostat off the wall and jumped the fan (green) and the red power line from the air handler and the fan turned on. I checked everything on the furnace side and it looks good.
When I popped the thermostat back on, it is now giving me an E79 no power to the common wire. I re-stripped the wires and measure the voltage between them at 28V. When I look at the equipment screen, it's sensing both external power wires and showing "power" at the Rh port but it highlights the common as not having power.
Super confused at this point, any suggestions?
11-22-2022 01:57 PM
I'm sorry for the trouble this may have caused you, and I appreciate that you've tried some steps; let's see what's going on.
It appears that your thermostat detects a wire at the C terminal but can't complete a circuit. To isolate:
I'll look forward to your response.
11-25-2022 02:04 PM
I wanted to see if you still needed help. Please let us know if you have any other questions or concerns.
11-26-2022 02:18 PM
I'm just checking in to make sure that you've seen my response. Please let us know if you have any additional questions or concerns before I lock this thread in 24 hours.
11-26-2022 03:28 PM
I ended up wiring the common wire directly from the furnace and problem was resolved.
11-28-2022 06:36 AM
Awesome! Thanks for getting back to us, @Malangon. I'm glad that you were able to figure it out.
So I'll lock this thread after 24 hours. If you have any other concerns or questions, please feel free to create a new post.