87 m6 AC fuse blowing

[emccallum]

I just picked up an 87 m6 in very good condition but it has a few minor issues. Fuse #20 blows as soon as you turn the key on. I unplugged the heater blower still blows. Unplugged the blower swap relay, no change. Finally when I unplugged the AC blower and transistor the fuse quit blowing. I thought maybe the fan was locked up, so I removed the dash and the fan spins fine and runs when powered with leads. Pulled the fan transistor and it looks pretty unique. I am not sure if my issue is the transistor or the actual fan speed switch on the dash. I bought both of these (used switch) and going to start fresh. Curious if this is a known transistor mod?

20200211_224427.jpg

[DesktopDave]

I'm no an expert, but that looks a like a hack job. Might have been functional at one time...

These cars do always come with a history, it's always fun to pull apart previous owners' fixes and give them the love they need. I'm hoping that the washer on the right is a pre-83 penny...solid copper is best for delicate electrical work.


I'd be worried about other fixes based on this picture, I'm glad it's in good hands! I couldn't find the part at RealOEM, it's in the diagram but not listed. There's a lot of threads about upgraded replacements. Check out this thread over at BigCoupe. Yours might be too far gone to 'rebuild' with a new transistor, but I'm sure someone has an original. I'll go check my stash for a late model A/C fan controller if you're desperate to have A/C.

[emccallum]

Dave, Thank you for the reply I certainly appreciate the help. I haven't checked the pennies date! I didnt run across that thread in my search, very helpful. My plan is really to fix the few issues the car has properly and keep it for a good while. Waiting for the transistors to come in the mail.

I am concerned I have some other issue, as all the threads I read talk about fan speed going wacky. Mine is blowing the fuse, and I havent heard that issue before. Hoping this wacky mod is causing some kind of short. If not, then fan switch and A/C switch. Both fans work when powered with leads.

Other upcoming fixes: Rear suspension bushings, steering rack repair, and one day in the future the leather dash.

[DesktopDave]

It's possible that the transistor is internally shorted; they don't last forever. Less likely, but also possible, is a problem inside the HVAC controls. Some 80s BMW fan speed controllers also include over-limit protection in the form of a little bimetallic spring. It operates like a breaker but fails like a fusible link.

[emccallum]

Dave,
Got it fixed today. I took the center console out replaced the transistor and it started working. Great. Put it all back together and turned it on and it blew the fuse. Needless to say I was devastated as I did a very careful job putting everything back together. It turns out that the connector going to the A/C transistor was loose. I tightened the metal tabs on each post and it is working fine. Crazy.

[DesktopDave]

Glad it ended up being something simple! That AC fan shouldn't cause trouble for another 30 years now...