Help! New Furnace; New Battery; Weird Combo.

[MTsafari]

We replaced our furnace in our '70 Safari a year ago. Has worked great with no problems. Over this past winter our existing battery went kaput, and we bought a new one today. As soon as we connected the new battery the fan on our furnace kicked on and stayed on. (no gas on to feed the furnace- just the fan), Even though the thermostat was off....

Any idea why this is happening?

[azflycaster]

Check the contacts in the thermostat, they may be shorted together. The cover will just pull off and you can see the contacts.

[MTsafari]

Thanks. So this is atypical? I will go pull off the cover now and take a look.

[garry]

I would not call it typical but a good possibility on the cause of your problem since the thermostat starts the sequence to turn on the fan.

[MTsafari]

I think the thermostat looks ok.
the connections still look like new.

[MTsafari]

Here's a picture:

[azflycaster]

Someone replaced the original, but it is just a switch anyway. Try removing one of the wires and see if the fan stops. One wire is 12 volts and the other returns the 12 volts to the furnace when the contacts are made.

[MTsafari]

We replaced the original furnace and thermostat a year ago. But all has worked perfectly up until today, when we replaced the battery with a new one... I'll undo the connections and see what happens...

[aircooled4]

Just a thought...unhook one or both of the wires going FROM the thermostat TO the furnace...that will eliminate the thermostat as the problem...THEN reconnect it...and unhook the wires AT the furnace coming FROM the thermostat...that will eliminate that and the wiring as the problem...