I have a Goodman furnace (gmpn080-4 Rev B). I want to install a new T-stat that is in need of a "c-wire". I have an extra wire in my bundle that is not being used that I could use.

I currently have a Honeywell t-stat that is only using 4 of the 5 wires, White (heat relay), Green (fan), Red (power) and Blue (cooling which connects to the screw labeled Y on the t-stat). All the rest match up to the correct color.

Here is my problem. I found on the internet a way to id the C-wire. Using a tester, touch the Red with each of the other three wires. If it jumps to 24V, then that is your C-wire. Since I am only using four wires right now, I did not expect to find one. The problem is, that I did. My white wire jumped to 24V when I touched it with the red wire.

So how do I wire my new t-stat if the white wire is both the heat relay and the C-wire? Can I split the wire and connect to both terminals (White and "C")?

Thanks for your help

I don`t understand what you are trying to say, but the common wire has to be a total seporate wire used for nothing else but common
At the circuit/control board you should find a wire hangin loose (usually blue) this would be common tie this wire to one of the extra wires you have going to tstat,then hook that colored wire to c post on the tstat

Yeah, I get that, but the current white wire is coming is as 24V, is that normal? I can use my extra wire to be the common, also a 24V.

I am just confused as to why my current white (heating) wire is already 24V. I didn't expect that, but if that is the way it is suppose to be, then great.

So I won't have a problem having two wires coming into the t-state that are 24V? The white wire and my new common?

Here is a link to my board. (http://www.alltemp-hvac.com/gmpn.pdf, last page). I don't have a Common terminal off the board, only white, green, and red.

Thanks for you help and patience.

And are you sure its not set for heat while you are testing, are you removing wires from tstat while testing
Comeing from the airhandler you should have only (1) 24 V hot wire "red" the tstat then acts as a switch sending 24v to whichever wire that its set for
Hope this helps, hang in there you1ll get it figured out

OK, I think I got it. I think I did have the heat on. Now this is all starting to make sense. I think I need to have my extra wire connecting to the blue wire in my furnace, which is the ground. That should give me power to the tstat at all times.

Good for you,,

Woohoo! After a brain hiccup, I figured it out. Thanks for all your help wmproop. Greatly appreciated.