Re: HVAC Microswitch Repair (archive)

Mike:
I recently went through what you did with HVAC in 86 735i after viewing archives here. I also had bad blower motor, though...had it rebuilt. Did you rebuild the microswitch when you had the assembly out? It requires drilling out the tiny rivets and popping off the cover, then lightly sanding the contacts? (Reminded me of a miniature set of distributor points.) I think that, in my case, that did more to cure my probs than removing/cleaning the button assembly. Now my HVAC system reacts to changes in temp selector or button actuation instantly. I recommend it for you if you haven't done it. The archive link to the instructions is no longer valid, so here are the instructions as I recall them, as follows:

1) With the thumbwheel board out of the dash, remove the cover screws (3) and the cover from the board.

2) Drill out the two rivets that hold the microswitch to the board. The microswitch is the tiny black box in between the two thumbwheels...the only thing there with 2 rivets in it. (Make sure you hold the switch in place as you drill out the rivets or the switch will spin and shear the third rivet, which holds the switch and its solder lugs to the board.)

3) Remove the lid from the switch by hand.

4) Lightly sand both contacts for the switch with a very fine sandpaper. (I used 600 grit.)

5) Replace the lid and secure it to the board through the old rivet holes with 2 (approx. 2.0 x 10mm nuts/bolts. Because I didn't have any handy, I used a short piece of plastic-covered twist-wire tie, and then glued it in place. It's very secure.

Jens- I am posting my followup to the board instead of emailing you since someone else might benefit.....

To the board: I emailed Jens 2 questions, one on a leaky steering gearbox and the other on the always challenging HVAC controls on my '84 733iA.

Good news and bad news:

1. I brought up the ATF Fluid (I didn't know they didn't make Dex II products anymore) with a Valvoline Dex III product and the steering seems to be operating much closer to normal. This leads me to believe it may only be a leaky hose instead of a bad gearbox. If anyone can tell me if they've had loss of P/S oil on a 733, please share your diagnoses. I am waiting to see how this goes.

2. HEAT:
I took out my microswitch and pushbutton switch on the HVAC and cleaned it all up and reinstalled. I saw the fix instructions on this excellent link and followed the very well photographed directions:

http://home.attbi.com/%7Efongman/repairpages/HVACmicroswitch.htm

While I had it out, I noticed that there was a burn pattern on the pushbutton control module (on the long connection tab in back) closest to the "Up/Down" or "Recirculate" end of the module. Other than that it was a little grimy so I cleaned up and put back together Note that it's very important to keep track of that pesky little ball bearing and spring on the Volume thumbwheel and make sure you don't install the notch past the switch when you reassemble.... you'll know what I mean...it'll lock up behind the switch {:-[)
After some unusual functioning it is back to it's earlier state: all buttons light up when depressed but it still only sends air to the defrost and ignores the pushbuttons. The air volume will increase when cranked up. I can't tell if the temperature changes when that thumbwheel is moved.
It seems like everything wants to function but it's not switching from the initial defrost stage.

Thanks for any further information everyone.

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