Monday, June 04, 2018

Smart Theromastats Aren't

After the joy of Saturday there had to be a balancing act on Sunday.

Our thermostat had gone T.U. over the winter - that's Thermostat Unresponsive, of course.

So I went ahead a bought a NEST thermostat - checking their website for compatibility and even got a nice energy saving rebate.

Per their website, with the 4 wire setup I had, it should work.

Well, not so much.

Overall the install was pretty easy. Between the instructions and YouTube videos it's pretty hard to mess up installing a NEST.

When I first installed it in the winter it started constantly cycling the furnace fan on and off.

It turns out I needed a fifth wire, a C wire. While NEST says it's thermostats doesn't require a C Wire, they typically do. Unfortunately, most of these "Smart" thermostats whose manufacturers were dumb enough not to think that most houses do not have a C wire and wouldn't an onboard replaceable battery (just like the thermostats they're replacing) be a smart idea? Thse thoughts apparently never crossed their minds.

And therein lies the problem.

The thermostat is located over the slab. the wiring to it may very well go up to the attic and then down to the furnace but we can't seem to trace it as it doesn't immediately go up from the thermostat but down and then around somewhere.

Even better, at the furnace the wire bundle has a fifth unattached wire that doesn't make it up to the thermostat - oh, and did I mention the wire colors are completely different and the ones at the furnace don't even match standard coloring schemes? Someone clearly spliced and connected the thermostat wires somewhere, likely behind the drywall and I'd rather not rip apart the house to find it just to try and run a C wire to have a thermostat.

So one solution proposed was to disconnect the G wire on the furnace and move it to the C wire terminal on both furnace and thermostat.

This worked well through the winter but guess what we found out the first day it got hot out?

The A/C will not run without a G wire.

I've tried both the Venster Add a Wire and the Lux Products Power Bridge add a wire solutions which are supposed to fix this issue, and both failed in weird ways. Venstar would not provide consistent power to the NEST and the A/C would not respond at all, but the fan would run - constantly when the NEST was plugged in, and the Power Bridge would provide lots of power but the NEST reported the G wire had a problem and would not work.

I've spent more time running up and down stairs, flipping breakers, and adding and removing wires to the furnace and testing the thermostat more times than I can count, and it took abut 4 hours plus yesterday trying without success to make the to make the add a wire solutions work, complete with the fun of some old furnace wires breaking, requiring me to strip new ends and expand my vocabulary, a lot.

I now have a plug-in 24 Volt adapter on order and we'll see if adding that as an external power source and moving the G wire back to G lets this thing finally run right.

So yes, if you don't have a C wire, I'd have to recommend holding off on getting a smart thermostat as they're not smart enough to handle the lack of a C wire.

Yeah, it's an annoying first world problem all right.

1 comment:

Mack Culverhouse said...

Jackie and rented a house in Savannah for the week on our Honeymoon. Rental had a NEST. Being late Spring, it's stupid little smart brain couldn't handle rapid temperature swings. It was miserable. But led to a hunt for air conditioned bars and museum.