# replacing a analog thermostat with a digital one



## Trainelectric (Feb 12, 2010)

replacing a honeywell T847R1871/Q674L1736 thermostat/base combination with a Honeywell TB8220U1003 touchscreen thermostat.

Found the drawing for the T-stat/base, and it's pretty self explanitory except for what to do with the Black "X" emergency heat lead.

Assuming that I did the right thing with putting the white "aux heat" wire to W1.

Thanks

Steve
aka Trainelectric


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## DuMass (Jul 7, 2009)

I can’t seem to locate a wiring diagram online for the old discontinued T-stat so hard to say. :sad:
Is this a single or multistage heat pump system?
Also, what did the black wire on the T-stat “X” terminal originally connect to on the equipment end?

Terminal “W1” looks correct for Auxiliary Heat according to the wiring diagram for the new TB8220, as long as that's what the white wire was originally connected to in the equipment.


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## Trainelectric (Feb 12, 2010)

*There's a reason you can't find a diagram*

it's because I'm dyslexic.

The thermosat I have is a T874R1871/Q674L1736. I had the second and third numbers reversed. ( I am a charter member of DAM, Mothers against Dyslexia)

The drawing is here, on page 6.

http://customer.honeywell.com/techlit/pdf/69-0000s/69-0392.pdf

The black wire on "x" is the emergency heat wire. I currently have it capped off.

Thanks for the reply.

Steve

AKA Trainelectric

"never underestimate the perversity of an inanimate object"


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