Heat/ac/defrost know blows fuse.

[98mst]

Hey everyone, been lurking for a few years finding solutions to other problems and always had success. But this time I need to make a post.

I have a 1998 Mercury mountaineer with the 5.0 with 254891 miles. At some point it starting blowing the number 10 ( 7.5 amp) fuse on the fuse panel inside the driver's door. I lose blinkers, cruise control, rear defrost and found out this summer it also takes out the ac. Eventually I narrowed it down to the heat/ac/defrost knob (is there a better term?) As the problem. Any time I turn it, the fuse pops. I've had yhe dash apart and looked at wiring and have found nothing exposed or broken. It's my daily driver and while it's not a huge issue, using the defrost this coming winter would be nice.

Any info or suggestions would be great.

 

[gmanpaint]

Congrats on your first post! Welcome to the forum.

To me it sounds like you have a ground issue somewhere in that circuit. Could be all the way in the back, in the column, or in the dash harness all wrapped up. Have you done anything anywhere near any of these items in the past, that could have pinched/cut a wire? Lights, stereo, speakers, etc...

I would start there, and go over everything very closely. Check behind trims, carpet, etc... If nothing found, find someone with access to Alldata, (or something similar) and get the wiring diagrams for the switch circuit, and trace everything it is connected to. A multi meter can check for continuity, in each circuit. This is not an easy task, and I even struggle with these types of repairs.

If nobody responds in a day or two, just bump this thread, by posting in it again, so others can see it, and hopefully offer more help.

 

[RandomNerd2000]

At the age and miles and low price of another knob out the junkyard, it might would be worth just changing the knob assembly.

 

[98mst]

Due to time constraints I'm going to try a new knob first found 2 explorers that had the dash already ripped apart. 1 had the knob intact but I don't know how long it had been exposed to the elements. Ordered a new one for 32 bucks. Thanks guys.

 

[delexploder]

Unplug the heat/ac blower motor and run two jumper wires to it to make sure it works , ive seen a few either siezed up or jammed with rodent nests blow the fuse

 

[Turdle]

Look inside the power distribution box under the hood. Check the blower motor relay socket for heat damage.