switching from an old Honeywell T87F (dial type) thermostat.... on the old tstat it was:

Wire - Terminal
Red - R
White - W
Green - G
Yellow - Y
Grey - B (but this wire wasn't connected to the transformer on the other end)


I tried just using the recommended wiring scheme that honeywell's site said, which is the same as above with the exception of the B terminal and the Grey wire. No go, wouldn't turn on the fan, heat, or A/c unit.

there is a common terminal on the transformer that doesn't have a wire connected from the set that goes to the thermostat (the grey wire is just taped back and not in use). i tried hooking that grey wire to the common terminal on the transformer (in the furnace) and connecting that to the C terminal on the backplate, but still no dice.

any advice would be great. thanks.

midnight wrote:

switching from an old Honeywell T87F (dial type) thermostat.... on the
old tstat it was:

Wire - Terminal
Red - R
White - W
Green - G
Yellow - Y
Grey - B (but this wire wasn't connected to the transformer on the
other end)


I tried just using the recommended wiring scheme that honeywell's site
said, which is the same as above with the exception of the B terminal
and the Grey wire. No go, wouldn't turn on the fan, heat, or A/c unit.


there is a common terminal on the transformer that doesn't have a wire
connected from the set that goes to the thermostat (the grey wire is
just taped back and not in use). i tried hooking that grey wire to the
common terminal on the transformer (in the furnace) and connecting that
to the C terminal on the backplate, but still no dice.

any advice would be great. thanks.

You've probably fried the transformer.

hvacrmedic

"midnight" wrote in message
...

switching from an old Honeywell T87F (dial type) thermostat.... on the
old tstat it was:

Wire - Terminal
Red - R
White - W
Green - G
Yellow - Y
Grey - B (but this wire wasn't connected to the transformer on the
other end)


I tried just using the recommended wiring scheme that honeywell's site
said, which is the same as above with the exception of the B terminal
and the Grey wire. No go, wouldn't turn on the fan, heat, or A/c unit.


there is a common terminal on the transformer that doesn't have a wire
connected from the set that goes to the thermostat (the grey wire is
just taped back and not in use). i tried hooking that grey wire to the
common terminal on the transformer (in the furnace) and connecting that
to the C terminal on the backplate, but still no dice.

any advice would be great. thanks.


--
midnight

Was the new stat compatible with the system? Time for a VOM and check
voltage. If the transformer is not putting out then you will need a new
transformer as well.

On Tue, 1 Nov 2005 09:44:10 -0700, "SQLit" wrote:


"midnight" wrote in message
...

switching from an old Honeywell T87F (dial type) thermostat.... on the
old tstat it was:

Wire - Terminal
Red - R
White - W
Green - G
Yellow - Y
Grey - B (but this wire wasn't connected to the transformer on the
other end)...

And I think they are saying you shouldn't have connected it.

Was the new stat compatible with the system? Time for a VOM and check
voltage. If the transformer is not putting out then you will need a new
transformer as well.

When my furnace/AC was about 5 years old, the AC stopped working. I
traced it to the transformer and went to a supply store where they
said it was part of the control panel and was about 200 dollars.

I whined a bit and he offered me a plain transformer for about 10
dollars,.

It looks sort of funny mounted elsewhere inside the furace but it's
been working for more than 20 years.


Remove NOPSAM to email me. Please let
me know if you have posted also.