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Subject: HVAC microswitch repair instructions Author: DavidC (moderator) : member since December, 2003 : 11918 posts Posted on: 2004-04-27 22:01:19

If your HVAC control panel appears to be dead except for the defrost function, the microswitch in the fan speed wheel (the Oreo-cookie wheel on the left of the panel) may be the culprit. If you're capable of handling a soldering iron and small screws, you can do this repair yourself and save the $200+ price of a new module from a dealer.

First, go to your local Radio Shack and get the following item:
Submini Lever Switch, part number 275-016A

You'll also need the following tools:
Soldering iron and solder
Small and large philips screwdrivers
Tin snips (or needle-nose pliers with a cutting end)
Vice-grip or equivalent locking pliers

Remove the radio from your vehicle to access the two 6x12 bolts securing the bottom of the HVAC control panel to the dash. Reach in with you hand on the left side and unplug the large rubber hose (do not disconnect any of the small colored vacuum lines). Remove the four small philips screws from the top of the plastic panel where it meets the dashboard. The entire panel can now slide out of the dash.

Remove the four screws holding the HVAC panel in place. Take note of the position of all the bulbs and connectors, including the two little wires on the underside of the pushbutton assembly. For info on how to remove the HVAC control panel from the dash and how to separate the cookie-wheel circuit board from the pushbuttons, see my other article, HVAC pushbutton repair.


Once the HVAC panel has been removed, remove the two screws on either side of it to separate the upper and lower halves.


Remove the upper half containing the fan speed and temperature wheels. Set the fan speed wheel to position 1 (actually, anything other than the "0" off position is fine).


Remove three screws on the back of the circuit board. Carefully pry the two tabs on the outer edges to release the circuit board, taking care not to allow the wheels to turn or come loose -- it contains a spring and steel bearing ball that are difficult to get back in place if they fall out. Set the wheel assembly aside for now.


Turn the circuit board over and locate the microswitch. Notice that it doesn't have a metal lever like the one you bought from Radio Shack.


Open the Radio Shack microswitch. Use a pair of locking pliers, such as vice-grips, to gently pull the metal arm out of the assembly. It will come out, but ...


Be careful not to cut yourself on it as I did.


The new (left) and old (right) microswitches.


The old microswitch is secured to the circuit board by the three soldered legs and by two metal rivets. Turn the circuit board over and drill out the two rivets using a 5/64" drill bit. You only have to go deep and wide enough to get rid of the lip that fits over the surface of the circuit board.


Now clip the three leads as shown above, leaving enough of the metal in place for soldering to the leads of the new microswitch later. If the microswitch on your particular board has wider legs with holes in them, you'll need to desolder them using a "solder sucker" (also available at Radio Shack), then solder in new legs using pieces of wire.


Remove the old microswitch.


Place the new microswitch on the circuit board in the exact same position. You can use the rivet holes as a guide. The Radio Shack switch is slightly wider than the original one, so you can actually slide the unit up to 1/2 mm more to the right and still be ok. I used Crazy Glue to secure the new microswitch to the circuit board, but you could use epoxy or new rivets, if you have the tools.


Solder the three leads of the new microswitch to the legs on the circuit board. Reassemble the unit and you're done!

David Cecil
'97 740iL, 120k miles
'86 735i, 91k miles
'77 320i, 140k miles

www.e38.org has links for everything about your BMW 7-series automobile

• HVAC microswitch repair instructions (pic) (url) - DavidC 2004-04-27 22:01:19 (10384 views)
  • Great post, just one suggestion... - Jeff '84 733i 5-Speed 2004-04-28 11:52:17 (860 views)
    • Yeh..that's what I did when I replaced mine..glue may overheat? (nt) - Kevin '86 735i VA 2004-04-28 18:58:50 (649 views)
      • I don't think it will overheat. The new switch should last for many years, but - DavidC 2004-04-28 23:22:58 (919 views)
    • That's a really good idea. I'll do that on the next one. (nt) - DavidC 2004-04-28 12:10:36 (639 views)