Exhaust fan keeps running

[56FordGuy]

I just bought a house with a propane furnace in the walkout basement and propane backup generator outside. The generator hasn't run since I got the house, the battery had failed. I replaced the battery today, programmed the auto test feature on the generator, and then tested it per the manual by tripping the main breaker to the house. Generator works fine, but since doing that the exhaust fan on my furnace in the basement runs continuously. It's attached to a duct like pipe that's open about 4" off the floor, then goes through the fan to a vent outside.

The fan has two wires to it that lead down to what looks like a relay. The relay has 5-6 wires coming off of it. I'll get a picture in a few minutes. I don't recall the fan running like this before I shut the power off to test the generator.

Any ideas would be welcome.

 

[56FordGuy]

Alright, let's see if the photos work properly.

This is the system.



In the above configuration, the fan runs continuously.





In this configuration, the fan does not run.




There's one black and one white wire that come out of the electrical box on the right. The white goes straight up to the exhaust fan, the black goes to the center pole on the relay. On top of the electrical box there's a smaller apparatus with two very small wires that go to the relay. I assume these are the control wires. When I disconnect the control wires, the fane keeps running. When I remove the center wire on the relay (assuming that's power in on the load side) the fan shuts off. It seems like the relay may have stuck closed when I flipped the main breaker to the house. Is this a logical idea, or am I missing something somewhere? DC electrical I understand, AC and the switches/ sensors on a gas furnace I have less experience with.

 

[Jlarson]

Ah nothing like a 903 relay tek screwed to the side of a furnace with 120v on the faston terminals. That would have been a good job for a RIB relay.

The pin out for those relays is:

Pole 1
1- Com
2- NC
3- NO

Pole 2
4- Com
5- NC
6- NO

The coil is the 2 at the bottom, sometimes labeled A1 and A2 or sometimes not labeled.

Check the coil with a meter, figure out where the coil power comes from and what the wires on pole 2 do.

 

[LS6 Tommy]

It seems to me the black line voltage wires on the relay are wired "normally closed", so the exhaust fan runs all the time except when the relay is energized. Just a guess, but maybe its a home made exhaust fan for humidity control that shuts off on a call for heat so you don't backdraft your chimney. The other two white low voltage wires are "normally open" so my guess is they probably lock out the heat when the exhaust fan is running. The bottom red and white low voltage wires on the bottom terminals are the coil. Whoever set that up didn't do a very good (or safe) wiring job. That relay has to be in an enclosure.

Tommy