Need HELP in a hurry!!!!!!

[papadan]

Have a central forced air furnace and central air system. Thermostat set to fan only works right, Set to furnace and everything works right. Set to Air cond. and compressor kicks on but fan will not work. Pressure line is cold and return line is hot as normal. had an old programable thermostat with out any papers on operation or hookup. Replaced and problem stayed the same. Ideas please?:confused:

[ToUtahNow]

You need to get your voltmeter out and trace the lines out. If the compressor is coming on it is not likely a thermostat problem.

Mark

[wbrooks]

Common Wire Names:

R or RH - HEATER TRANSFORMER
W - HEATING CONTROL
G - FAN RELAY
C - 24 VAC COMMON (optional)*
Y - COOLING COMPRESSOR
RC - COOLING TRANSFORMER

http://www.nexicom.net/~wbrooks/4wire.jpg
I think your furnace controller may be cooked. You can try opening up the furnace to access the wiring diagram. You may have a set of cooling delay switches that are usually set for 0 sec delay but can be set for up to 3 min. Try open and close the switches maybe they are dirty and not making contact.
The only wire from the thermostat that controls cooling is the "Y" wire (and Rc - return), the fan is turned on by the furnace control board so if the A/C compressor turns on then the thermostat is working correctly (also proved by swapping them). Maybe try to find the cooling fan relay and give it a cleaning

[papadan]

Thanks Wayne, the new therm. is wired correctly. The blower works with heat and fan only, just not with AC. I will get a look at the board and any relays tommorow

[wbrooks]

If your hot there is no harm in setting the fan switch to on and letting the A/C cycle as normal, I have run mine like that in my last house to try and keep the upstairs cool

[papadan]

Got to check out the furnace today and found out someone had disconnected the blower wire from the control module. Guess I should have taken a closer look before asking. Thanks everyone. Dan

[wbrooks]

Would that be the same SOMEONE that took the blower out this spring to clean it ;)

[papadan]

Would that be the same SOMEONE that took the blower out this spring to clean it ;) Wink Wink!!!! My son just bought this house as is from an estate forclosure. :eek: Have found several strange little things around there, like the outside faucet was connected to the hot water line and the front door light switch was a double pole N.O. / N.C., when you turn it on the porch light went out and the inside ceiling light came on.:eek: :confused: :D

[HVACMAN1]

One or more of your wires may be crossed down along where they are stapled to a wooden post. Check to see if a staple or nail cut through any of the wires.:)

[sluggo85024]

????:confused: HVACMAN

[Robert Luland]

Give it a break already. Go to the unit> Pull the panels> Tape the door switch> If you got 24V+ between common and G you got ether a bad fan control board or a bad motor. Bob

[tomgeer]

if the problem was there befor you changed the stat and there after you changed the stat, the problem may not be the stat. make sure your "g" terminal and "y" terminal are bothe getting a 24v signal at the furnace. If so the problem is with your circuit brd or fan relay. Call your local Service Expert co. to help. Good luck.