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[robash9608]

I've tried to search for this specific question and I haven't had any luck. I am installing a friends outdoor furnace and I'm down to the thermostat. He's got an oil heat furnace in his house with a two wire thermostat. He also has an air conditioner package unit that sits outside. The a/c thermostat sits right beside his oil furnace thermostat. The condensor in the a/c unit has went bad but the blower still works. The a/c thermostat looks like it was originally a two wire and someone has added a third wire and wrapped it on the outside of the casing. Finally, my question: How can I wire the a/c thermostat to control only the fan in the a/c unit. There are 3 wires at the unit, green, red and white and same three wires at thermostat. Red is on RC, Green and White are both on G. The guy replaced his a/c thermostat about ten years ago when the condensor went bad (he thought it was the thermostat) and he said he may have the wires backwards.  Any help would be greatly appreciated!!
Thanks!

[RSI]

Red is on RC, Green and White are both on G.

Are those on the same connections at both the thermostat and cooling unit?

Can you get a picture of the connections in the cooling unit? Normally the you would use the RC and Y for A/C.

If it is wired normally, you would connect the wires at the thermostat end to RH (red) and W (white). Then at the other end you would connect the red to the RH if there is one or to the RC if it is the only thing there. Then the white should go to the G terminal.

[robash9608]

At the cooling unit, the three wires do not go to a certain strip, they go straight to the devices. If I remember right, the green wire is going to a relay, red to a transformer and the third wire goes to another component. I'll try to get a few pics tonight.

Are you saying that I only need to use two wires? At the thermostat, remove red wire from RC and place it on RH and White wire on W. At the Cooling unit, Leave the red hooked to RC and then wire the White to the G..

Thanks

[RSI]

Yes, that is correct at the thermostat end. If there is a jumper between RC and RH then you don't need to move that wire.

At the other end, it will depend on what it actually connects too.

If your thermostat needs power then you will need the 3rd wire. (usually only digital thermostats without batteries will need it)

If the green wire is going to the relay, check what is on the other side of the relay. If it is to run the fan then you will either need to switch it to the white or just connect the green wire to the W on the thermostat instead.

[robash9608]

OK thanks, I'm having to work late tonight. I'm going to go there tomorrow to wire it. Thanks again for the help

[robash9608]

Wired it the way you said and it worked perfectly! Thanks again!