WiFi Thermostat Wiring

Did you put the access door back on the furnace to engage the door interlock?

57TinkerMan said:

Did you put the access door back on the furnace to engage the door interlock?

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Yes, I did. At least, I thought that the panel was all the way closed. After it didn't work, I ended up putting the old thermostat back in place.


So, are you indicating that it should have worked?

First, see if you read 24VAC across COM ("C") and R. Then check the other end of those same wires at the thermostat end of the cable. If 24VAC there, then the T-stat should power up.

That "extra" wire could also have been broken or damaged as well. If you have 24 at C and R at the furnace board with the interlock switch pushed in, then see if you have it at the stat, if not it's either damaged or there's possibly another junction in between where they didn't bother carrying that wire through to the thermostat.

CC

ClimateCreator said:

That "extra" wire could also have been broken or damaged as well. If you have 24 at C and R at the furnace board with the interlock switch pushed in, then see if you have it at the stat, if not it's either damaged or there's possibly another junction in between where they didn't bother carrying that wire through to the thermostat.

CC

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I guess that I am a bit confused. I thought the C wire was to give 24V to provide power to the WiFi thermostat. At least that is what the install instructions for the thermostat seemed to be indicating. If that is the case and R is 24V, then a voltage potential between R and C would be zero.

gpraceman said:

I guess that I am a bit confused. I thought the C wire was to give 24V to provide power to the WiFi thermostat. At least that is what the install instructions for the thermostat seemed to be indicating. If that is the case and R is 24V, then a voltage potential between R and C would be zero.

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Yeah, they don't explain it well. It took me a while, too.

There should be 24VAC between R and C. You need both to power a thermostat.

The old-style mechanical thermostats didn't need power. They just sent the voltage from "R" back to the furnace (or whatever) on one of the other wires.

Maybe it's easier to think of R as "hot" and C as "neutral." It may not actually be this way, compared with your house wiring, but with AC it doesn't matter. All that matters is the potential between them.

Thanks for the help. I got it working. Not sure why it didn't work the first time around. Maybe a bad wire connection or the panel switch not fully closed.