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Posted by: jmargush Sep 8 2014, 07:21 PM

Got home from the autox yesterday and noticed something running when I shut the car off. Thought it might be fuel pump but it wasn't. Instead it was the defrost fan behind the fuel tank.

I tried pulling all the fuses and it never shut off.

Any suggestions on where or what to look for?

Posted by: Dave_Darling Sep 8 2014, 11:02 PM

The relay may be stuck somehow. Certainly unplugging the relay should stop the blower.

The relay gets un-switched power on terminal #30. If the relay sticks, connecting 30 to 87, it will send power to the fan no matter if the ignition is on or not.

The switching should happen when the ignition is on and when the heater lever is up all the way. The former provides power to the coil in the relay, the latter provides the ground. Even if the wire to the heater lever shorts to ground, turning the key off should still stop the relay from connecting 30 and 87. So that means either the relay is faulty, or something is connected incorrectly.

Swap the relay for one of the headlight relays. If the light doesn't work (or doesn't stop going up and down!) and the blower works correctly, you've found the problem.

--DD

Posted by: jmargush Sep 9 2014, 04:11 AM

You mention the lever being up
Are you refering to the one on the floor? If so doesn't that just control the blower motor back in the engine compartment?

Posted by: BeatNavy Sep 9 2014, 05:01 AM

Yes, the lever on the floor. Pulling it up opens the flapper boxes to allow heat from the exchangers to pass through the longs and into the passenger compartment. As Dave said pull that lever up high enough and it grounds the blower motor circuit so the blower motor gets power and runs (assuming the relay is working correctly).

Posted by: jmargush Sep 9 2014, 05:45 AM

Does that lever also control the motor up front by the gas tank? Cause that is the one that is staying on

Posted by: bdstone914 Sep 9 2014, 06:03 AM

The heater lever does not control the defrost fan. It is probably the relay as suggested.

Posted by: Dave_Darling Sep 9 2014, 09:23 AM

Shoot, you did say "behind the gas tank". I should have realized you meant the fresh air fan. My advice was all intended for the heater blower, which is what I thought of when you said "defrost fan". Sorry about that.

I'm not sure what feeds the fresh air fan, except that one of the relays on top of the fuse panel sends switched power to it. And to lots of other systems as well. If you can figure out what else gets powered from that, check if those things are on or not.

--DD

Posted by: jmargush Sep 9 2014, 12:10 PM

Thanks
I'll check that relay board

Posted by: rhodyguy Sep 9 2014, 03:11 PM

did you try moving the fresh air control sliders?

Posted by: partwerks Sep 9 2014, 09:24 PM

I'd pull the ask tray, and see what's going on with that.

On mine, somewhere in it's past, the bottom contact has gotten pushed down, and looses contact with the top one. Hard to get in there and pull it up, but may be able to do it when getting the conversion done, and get better access.