I have 5 wires from my old thermostat.

Y- Orange Wire
RH - Red Wire
W - White Wire
G- Green Wire
RC - Black wire

When I connect up the unit according to the manual, I am left with the black RC wire.

On my old unit the RH and RC are not connect or jumpered together.

Where would this RC wire get connected to on the new T1800

Thanks
Mike

Brand and EXACT model number of the old thermostat?

Sorry - forgot to post that.

White -Rodgers IF87

Thanks

What kind of heat and cooling do you have?

Just a guess, but it looks you have a dual transformer system and the factory jumper was pulled from your old WR and wired for both transformers. Scratched my head on that Ventstar a while until I discovered it does not accommodate dual transformer. If everything is working then don't worry about that wire, other than to track down where it connects to the transformer and disconnect it.

White -Rodgers IF87

Sorry that number not listed in the White Rodger electronic catalogue and it goes back 60 years. Try again of find the complete number.

You may need that extra wire since if the A/C and Heat have different transformers The circuit will have to be complate and one transformer will not power both under those circumstances because the other leg of the 24 volts will not be available at the equipment.

The model is the 1F87-361 - sorry not the iF87...

I just spoke to the guy who installed my Air Conditioner and he told me I only have 1 transformer.

Is the above terminal label and wire color map from you WR? From the install guide here (http://white-rodgers.com/wrdhom/pdfs/instruction_sheets/0037-6763.pdf) RC and RH are your transformer power. Page 3 shows a two-transformer wiring.

Here is copy of old thermostats wiring and configuration menu.

http://www.white-rodgers.com/wrdhom/pdfs/06_Cat_pages/Cat_06_pg0178.pdf

If you are SURE you only have one transformer then you would not need to use all the wires.

Now you said that both the RC and RH were wired on the old thermostat so something is wrong with this picture because the black wire was connected to the old thermostat. Why it was hooked up? That is a unknown factor. Follow the black wire down to the furnace/air handler and see where it goes before you try and finish the job.

here is copy of old thermostats wiring and configuration menu.

http://www.white-rodgers.com/wrdhom/pdfs/06_Cat_pages/Cat_06_pg0178.pdf

If you are SURE you only have one thermostat then you would not need to use all the wires.

Now you said that both the RC and RH were wired on the old thermostat so something is wrong with this picture because the black wire was connected to the old thermostat. Why it was hooked up?? That is a unknown factor. Follow the black wire down to the furnace/air handler and see where it goes before you try and finish the job.

Agreed! We have contradictory info here. :confused: I thought it was just me that was confused.

He really needs to find out for sure how many transformers are in the system. The extra wire would not have been hooker to the old thermostat unless it was used. OR unless some dummy took out the jumper and ran the black all the way to the air handler/furnace to pick up the transformer again. LOL I have seen that happen.

PS fixed from thermostat to transformer.