We have a 20+ year old forced air propane gas with central air. The air conditioning was just installed last year and things worked fine. But since we switched from heating to air conditioning the fan will not shut off whether the system is in "heat" or "cool" or "off" and the fan in "auto" or "on". We were told we probably needed a new fan/limit control so we installed a new one of these, but we still have the same problem. We also tried and new thermostat and that did not solve the problem either. Both the air conditioner and heater work its just that we cannot stop the fan from running other than shutting off the electrical breaker.

Any suggestions??


I would appreciate some help on this.

You might have a stuckA/C blower relay. Check the diagram on the inside if the blower door to see if it is listed. If that relay shorts closed it will cause the fan to run all the time. So will a fan and limit control but you already replaced that part.

I would check the wiring at the terminals at the furnace, since it worked for the heating it sounds like a wire may be misplaced on the terminal board. Here is the way it should be wired, But the colors may not match your's so you may have to search it out:

At the furnace it should be:
Red on R
White on W
Green on G
Yellow on Y

Also there are two wires that go to the condensing unit the colors do not mater.

One wire goes to the Y with the Yellow wire
The other goes to the Terminal marked Com.

The same applies at the thermostat;
Red on Rh----with a jumper going to RC
White on W
Green on G
Yellow on Y

Good luck let me know if this helps