Ask Me Help Desk - No Power to A/C Thermostat

Here is a 4 heat/2 cool stat.

Buy Honeywell VisionPro IAQ Programmable Universal Thermostat with Total Home Comfort Control | Honeywell YTH9421C1002

I need to look at it a bit more.

Got some advice. Best one can tell there are 4 stages of heat.

You might consider jumping W1 to W2 to W3 assuming you have a 2 stage heating stat. From my advice, the air handler will sequence stage if the thermostat doesn't. It might provide better recovery on cold days.

I have a similar setup and problem. My question is: if there is no 24 VAC between R & C. the fuse is good, and there are no loose wire or connections that I have found. Is it most likely the board that is blown?

I have no fan when I switch tstat to fan on, and of course no a/c at all.

Thanks
Sgtaxe

Quote:

Originally Posted by KeepItSimpleStupid

This reads well. Kinda interesting reading.

I'd focus your immediate attention on the following two terminals. R & C.

The next time it fails check R & C at the furnace first and R & C at the thermostat. There should be 25 VAC between these terminals at all times.

Those two terminals should go to the transformer in the air handler. There should be 4 terminals or wires. Two go to 120 VAC and two go to R &C.

Look for any loose connections in any of these wires.

There also may be a 3 A automotive type fuse on the control board. Re-seat that.

You need 24 VAC between R & C for the tstat to have power.