furnacethermostatwiring
I am thinking about upgrading my Honeywell thermostat. Every thing I have seen describes / shows a single wire for each color. My current thermostat has two wires connected to each terminal (two green wires, two yellow wires, two black wires, and two red wires).
The new thermostat I want to install (a Nest) says to only insert one wire per connector. Is this a problem? Do I need to get my furnace rewired? Or, should I just keep the wires twisted together?
You can't simply connect any extra wire to the C terminal on the thermostat. You have to also connect the other end of that wire to the C terminal in the furnace.
If you include a photo of the wiring at the thermostat, and a photo of the wiring in the furnace I can give you a detailed list of instructions for hooking it up.
I've labeled your photo, which should help you understand what's going on.
What you describe as a "blue" wire at the thermostat, you describe as "gray" at the air handler. I can't be sure, since I'm not there, but I think they are one in the same.
If you want to install a fancy new WiFi thermostat, you're going to have to pull an additional wire from the air handler to the thermostat. Once you have that, you'll connect one end to the C terminal of the air handler, and the other end to the C terminal of the thermostat.
Best Answer
The answer is yes; it was a problem. The wiring wasn't done correctly. I had an HVAC guy come out. He suspected that whoever installed my thermostat cheated by using some lower grade wire and doubling them up. Sure enough when he untwisted the wires from the old thermostat and checked the voltage with a multimeter we saw that the pair would give us the necessary 24 volts but an individual wire would only give us about 17. Nice.
Anyway, I shelled out about $100 to have him run a real HVAC cable. (I had him use 10 wire just incase I want to make use of more of the new thermostat's features in the future).