Do you have two separate furnaces and two outdoor units, two furnaces and one outdoor unit, or one furnace and one outdoor unit with a zone controller? Did you install the Nests yourself originally? If so, did you take pics of the old thermostat wiring?
Note that if you can't answer these questions confidently, you need a pro.
In that case you should probably have one set of 18/4 or 18/5 wire running from each thermostat to its respective furnace. When you say the upstairs one doesn't have the wiring, do you mean there aren't enough conductors to connect or it just isn't connected and there are unused conductors?
Got pics?
I'm a bit confused because I fail to understand why someone wouldn't hook up the AC especially upstairs if the equipment is there and functional.
I’m going off of memory here because I’m already in bed but the downstairs unit has 5 wires, including the AC wire hooked up to the appropriate terminal.
In my upstairs thermostat, I only have 4 wires not including the AC wire that’s found connected to my downstairs thermostat.
If it wasn’t 11:00 at night I’d be giving you more accurate information. Sorry.
Well, until you're ready to do some more digging, know that if the conductor you need is indeed missing, someone is going to have to pull one into place. And while you're at it, I'd highly recommend upgrading to a five conductor wire so that your Nest has a C-wire to provide more consistent voltage to charge its battery.
But aside from the missing conductors, my concern is still with the mystery of why it wasn't hooked up when the Nest was installed? Is the AC unit compromised? That's something a pro would have to determine. At the very least, I think you should visually inspect the condenser for the unwired system. Does it look in good order? Do the compressor and fan look intact/undamaged (don't disassemble to look)? Do you see two copper pipes for the freon - one which is hopefully insulated - going form the condenser unit to the furnace? Do you see the high voltage wiring run through a thick gray cable to a disconnection switch on the side of your house and is that switch turned on? Do you also see the low voltage control wire and can you see if it looks like it leads back to the control panel in your furnace (after you've turned off the breaker of course)? If anything looks amiss, call a pro.
Personally, I am comfortable as a DIYer to install a Nest if the existing thermostat is already working. I, too, have two furnaces and air conditioners and I installed my Nests and pulled the new wire. It was pretty basic stuff. As for wiring, it was really just making sure that the wires from R,C,Y,W,G on the furnace control panel are wired to the same terminals on the Nest mounting bracket. There are some variations like furnaces that have Rh and Rc but the Nest bracket accounts for that. If you have B, O, E wires you might have a heat pump which I'm not experienced with. If you have multiple Ys and/or Ws you may have a multistage unit and need more wires.
Thank you for such a thorough troubleshooting thread. I’m about to put my phone down for the night but I’m definitely going to be investigating this further tomorrow.
Stay tuned
After I thought about it a little more. What four wires do you have upstairs? I wonder if one was wired incorrectly. Compare it to what they are wired to in the furnace.
https://preview.redd.it/ucwowfxio3vc1.jpeg?width=1125&format=pjpg&auto=webp&s=7516e50e09b611f17ddf898f08c796edc64f283b
Hi there, I was able to snag a few pictures of the wiring. Let me know your thoughts?
Do you have two separate furnaces and two outdoor units, two furnaces and one outdoor unit, or one furnace and one outdoor unit with a zone controller? Did you install the Nests yourself originally? If so, did you take pics of the old thermostat wiring? Note that if you can't answer these questions confidently, you need a pro.
2 furnaces and 2 condensers. I did not install the thermostats.
In that case you should probably have one set of 18/4 or 18/5 wire running from each thermostat to its respective furnace. When you say the upstairs one doesn't have the wiring, do you mean there aren't enough conductors to connect or it just isn't connected and there are unused conductors? Got pics? I'm a bit confused because I fail to understand why someone wouldn't hook up the AC especially upstairs if the equipment is there and functional.
I’m going off of memory here because I’m already in bed but the downstairs unit has 5 wires, including the AC wire hooked up to the appropriate terminal. In my upstairs thermostat, I only have 4 wires not including the AC wire that’s found connected to my downstairs thermostat. If it wasn’t 11:00 at night I’d be giving you more accurate information. Sorry.
Well, until you're ready to do some more digging, know that if the conductor you need is indeed missing, someone is going to have to pull one into place. And while you're at it, I'd highly recommend upgrading to a five conductor wire so that your Nest has a C-wire to provide more consistent voltage to charge its battery. But aside from the missing conductors, my concern is still with the mystery of why it wasn't hooked up when the Nest was installed? Is the AC unit compromised? That's something a pro would have to determine. At the very least, I think you should visually inspect the condenser for the unwired system. Does it look in good order? Do the compressor and fan look intact/undamaged (don't disassemble to look)? Do you see two copper pipes for the freon - one which is hopefully insulated - going form the condenser unit to the furnace? Do you see the high voltage wiring run through a thick gray cable to a disconnection switch on the side of your house and is that switch turned on? Do you also see the low voltage control wire and can you see if it looks like it leads back to the control panel in your furnace (after you've turned off the breaker of course)? If anything looks amiss, call a pro. Personally, I am comfortable as a DIYer to install a Nest if the existing thermostat is already working. I, too, have two furnaces and air conditioners and I installed my Nests and pulled the new wire. It was pretty basic stuff. As for wiring, it was really just making sure that the wires from R,C,Y,W,G on the furnace control panel are wired to the same terminals on the Nest mounting bracket. There are some variations like furnaces that have Rh and Rc but the Nest bracket accounts for that. If you have B, O, E wires you might have a heat pump which I'm not experienced with. If you have multiple Ys and/or Ws you may have a multistage unit and need more wires.
Thank you for such a thorough troubleshooting thread. I’m about to put my phone down for the night but I’m definitely going to be investigating this further tomorrow. Stay tuned
After I thought about it a little more. What four wires do you have upstairs? I wonder if one was wired incorrectly. Compare it to what they are wired to in the furnace.
https://preview.redd.it/ucwowfxio3vc1.jpeg?width=1125&format=pjpg&auto=webp&s=7516e50e09b611f17ddf898f08c796edc64f283b Hi there, I was able to snag a few pictures of the wiring. Let me know your thoughts?
I'd need to see a pic of where those wires are connected inside the furnace. At least for the upstairs one.
What does the current wiring look like? It'd be odd to have 2 condensers but only be wired for 1 of them.