Our move-in to-do list included replacing the original thermostat with one from the 21st century. I finally got around to it this weekend, and took plenty of pictures to keep track of the way things were wired, so now we have an installment of "Ben's DIY corner".
Popping the front cover off, you see on the middle panel that the thermostat is controlled by a spiral of metal that expands and contracts with changing temperature, tilting a little glass ampoule of Mercury to make or break a contact in the circuit that turns the HVAC system on and off. It's amazing that something so primitive can control temperature to within a degree.
Here's the wall wiring connected to the rear board of the original thermostat. There's a blue wire in there, not actually connected to anything on the old thermostat, that ran most of the way down to the HVAC unit in the crawlspace. The new thermostat requires the blue wire to be connected. Hold that thought.
All the greasy furry dust on those wires gave me flashbacks to the horror of this house as it was when we bought it. I'll spare you the unbelievably poisonous, acidic green paint that reared its ugly head again when I pulled the last piece of the old thermostat off the wall. Molly said, "seeing that sure takes you back" as I was sitting there thinking, "I guess, in a way, we'll never fully escape the trauma of prepping this place to move in".
Anyway, having to go down into the crawlspace to check out the wiring down there created an opportunity to sand and paint the wall, and let the paint dry.
Once I figured out which panel to pull off the HVAC unit, I tracked down the thermostat wires...
...
The blue wire I needed for the new thermostat was connected at the HVAC control panel itself, but, about six feet out from the HVAC unit, all the wires were spliced and hanging down about halfway between the floor of the house and the ground. The blue wire running from the thermostat wasn't attached to the HVAC unit control panel at that splice, so I had to strip and splice it (so it now shares a connection to the exterior condenser unit). Whatever.
Back upstairs, everything is now wired up all modern.
Somehow, nothing blew up, and the heat and AC seem to work.
Now I just have to run this little vial of horrifying neurotoxin to our friendly neighborhood hazmat disposal site, and we're done!
