Air Conditioning - installed new thermostat-HELP !

I just replaced my mercury-type manual thermostat with a new programmable White Rogers unit. When removing old unit, I noted that the color coding was not followed, but I noted color of the terminals the wires were connected to, and connected the wires to the same terminals (red to R, white to W, there was blue wire connected to G on the old unit, I also connected to G on the new, and there was Black wire connected to Y, so I did the same-connected to Y).

After all I went and checked connections on the AC/Heat control board: to my surprise, the black wire connected to Y terminal on the old (and new) thermostat, is connected to the C (COMMON?) terminal on the control board!
The Original control board went bad a few years ago, and I did have the control board replaced (by a pluming specialist) with universal White Rogers control board-model # 50A65-843 (universal integrated furnace control).
The heat and AC worked fine since then, and now they appear to work too.
The schematics/connections for the control board show that that Y on the board may be connected to the C on the board through "compressor contactor".

The manual for the board says: "2nd wire from Y terminal goes to 24 VAC HOT side of compressor contactor coil", and that C terminal is "24 VAC COMMON side of compressor contactor coil"

With the AC/Heat unit ON, thermostat disconnected, I checked voltage at the terminals: R seems to be "Hot"side, everything else is "cold" side.

The question: Should I leave everything the way it is - Y on the thermostat connected to C on the controller,

or should I switch the wire on the controller board from C to Y (that is how it should be?)

Thank you very much for your help- I have very rudimentary knowledge of electrics/relays/etc. but I just like to DIY...

Sorry for such a long question, I feel that the more info I gave you, the better.

We going to need more info of what you got.

Make and model of both indoor and outdoor unit.

We may have to start over fresh on this. Sounds like something is messed up.

We going to need more info of what you got.

Make and model of both indoor and outdoor unit.

We may have to start over fresh on this. Sounds like something is messed up.

Thanks, Jay-
indoor unit is Lennox Model # C23-51-1, cannot make outdoor-it's too dark now. Will look tomorrow.

How important is Model #s- I thought wiring was standard on similar units?
Thanks again.

Most unit are standard, but I want to be sure what we all have and get it wired right in the first place.

Also, let me know what wire you have in the wall and going outside.. (Colors)

Most unit are standard, but I want to be sure what we all have and get it wired right in the first place.

Also, let me know what wire you have in the wall and going outside.. (Colors)

Thanks for your help, Jay-
I believe it's wired right: the BLACK wire from the "C" terminal on the furnace is NOT the same BLACK wire coming off the thermostat.

1. The black wire from furnace "C" terminal does not go w/ the rest of the themostat's wires-it splits and goes somwhere into different conduit then 3 other thermostat wires;

2. the BLACK wire from thermostat's "Y" terminal does not go to the furnace -it goes together with the wire from furnace's "C" terminal.

In other words, they wired contactor directly to the thermostat, w/o going to "Y" terminal on the furnace.

Now is another question:the new White rogers thermostat can be wired so no batteries are needed, but it needs 24VAC "COMMON" wire. On the opposite side of the same wall where thermostat is mounted, there is 3-pole switch which seems to have both white and black wires in the box=120VAC..

If I managed to bring 120VAC into the box behind the thermostat, would it be possible to install very small 24 VAC transformer, and take that 24VAC COMMON from there ?

I don't think I can fish a wire down from thermostat to the furnace w/o braking some walls....

thank a lot again