Blower fans run all the time - without switch

Post in this forum for topics relating to the interior.

Moderators: GRNSHRK, ron, bfons

Post Reply
635911
Posts: 81
Joined: Wed Jun 15, 2016 12:33 pm
Location: Sydney, Australia

Blower fans run all the time - without switch

Post by 635911 »

Hi All,

This is a new (I think, after searching the forums) twist. Here is the story so far:

I have a 1986, Australian delivered 635 with A/C etc. It is in really good shape/unmolested. Some weeks ago the car started blowing fuse 20. I changed the A/C blower transistor (I think it was actually a short around this transistor, not the unit itself). All worked well at this point.

Last week, I had that terrible electrical smoke smell, and then blowers only worked on high. As per the great info on this site, I removed the dash blower fan controller, and just as the voices of experience had predicted, was a seriously fried original transistor.

I replaced the transistor with the beefier TIP3055, and here is where things went odd. reconnecting everything in the dash to test, the blower fans (one at a at time depending on A/C switch position) run on (very nearly) full blast, regardless of fan knob position. when I go full speed setting (micro-switch click), there is a slight increase in fan speed (again either heater or A/C depending on A/C switch position).

After pulling the controller apart (several times!) checking the transistor and its junction continuity etc, checking the variable resistor function etc, I put it all together and tested again. same issue.

Here is what seems odd to me. I then pulled the main (four connector) plug out of the speed controller. exactly the same behavior (ie fan on 90% , micro switch makes it 100%).

I pull the A/C switch out. exactly the same symptoms.

I have the ETM and can only guess that some 90% voltage is leaking in, but cannot understand where that might be.

I have had to pull fuse 20 to turn the fan off!

Any advice on troubleshooting this would be very gratefully accepted.

Toby
1986 635 CSi Lapis Blau with Anthrazit buffalo
1988 911 3.2 231HP Grand Prix white (Sold - 13 years of Zuffenhausen fun))
1984 BMW R80 G/S Dunkel Blau
1982 Yamaha SR500 scrambler
Pod
Platinum Member
Platinum Member
Posts: 4492
Joined: Tue Mar 16, 2010 8:32 pm
Location: usually in the barn, Kent, England.

Re: Blower fans run all the time - without switch

Post by Pod »

Try changing the transistor, or even try fitting another circuit board?
635911
Posts: 81
Joined: Wed Jun 15, 2016 12:33 pm
Location: Sydney, Australia

Re: Blower fans run all the time - without switch

Post by 635911 »

Thanks POD,

It's interesting that the car operates identically with or with out the controller plugged in. Or am I missing something?

I would love to try another circuit board, but they are not that common here in Oz.

I will keep looking.....

Cheers,

Toby
1986 635 CSi Lapis Blau with Anthrazit buffalo
1988 911 3.2 231HP Grand Prix white (Sold - 13 years of Zuffenhausen fun))
1984 BMW R80 G/S Dunkel Blau
1982 Yamaha SR500 scrambler
Post Reply