Microswitch cleaning and repair
Life has been great with my 735I. I bought it with 87,000 miles and the previous owner had just replaced the $400 HVAC electrical board. Inspite of what others have said my HVAC system had worked flawlessly until now. When it works right it's great, set the temp and forget it!
Now 9 years later and with 215,000 miles the microswitch is acting up. Here what's happening, when I turn the fan switch from off to on I hear the microswitch click but no green lights. At first I could click it back and forth to get it working. After awhile that didn't work. By then the only way to get it on was to leave the fan switch in the ON position turn off the ignition then back on. For some reason it didn't work with the ignition on and moving to on. Now it has finally stopped working at all but does click. If your led's light up but the fan doesn't turn on or your fan works intemittenly such as when hitting a bump. The blower motor brushes are probably worn out. Click here to see blower fan replacement.
To get at the microswitch, start by removing panel on right side of center console by glove box. Check fuse for continuity at left side of glovebox.
If you do have power at fuse go ahead and remove center panel. (skip the next two pictures) If you have no power at fuse,
check fuse 16 at fuse box.
If fuse 16 is good power may have been cut at AC pressure switches. I am unsure of how AC pressure switches are wired
into circuit. But if your freon is low the compressor will not come on possibly causing HVAC to not work.
Test for power from fuse 16 to Hi-lo switches at drier connector below. (Receiver drier is located at right front corner below air cleaner.)
If you have power then check for continuity at both switches.
Switches appear to be wired inline so they must both work for power to go through.
After cleaning and repairing my microswitch I've since found that unplugging the AC pressure switches doesn't effect HVAC pushbutton controls. My led's remain lit if pressure switches are unplugged.
To remove center panel start by removing radio then centerpanel screws and bolts.
Right side of console will pull out. To remove left side you must reach in through radio opening and
pull off rubber air hose from temp sensor behind radio.
I think 6 screws hold control unit to panel
Here's what you will find inside.
The switch appeared to work since it still clicked so I used TV tuner cleaner and sprayed it
into microswitch. This did the trick and the switch was now operational again.
If you plan on using brake cleaner test it first!
The chlorinated brake cleaner (Brakekleen) in the red can I've had turn plastic and electrical parts white. Use the blue unchlorinated and test first on some other electrical part!
Right pin seemed to work opposite of left. When switch wasn't pressed center pin and right pin had continuity opposite of left pin.
Upon reassembly check that spring and bearing are inplace. Dial should turn smoothly and click at first 3 stops.
Start reassembly, once you get everything together and plugged in turn on the ignition and try the switch.
With good luck the cleaning will get it working again. You can finish assembling it and enjoy your HVAC again!
Update: cleaning my microswitch lasted only a month. Then it started acting up again. If cleaning doesn't work for you then you will have to disassemble the switch and clean it as shown below.
After removing the switch you will have to drill out the third rivet which holds the switch together. Carefully remove the cover so that nothing flys out. I suggest you work on it inside a plastic bag so if the spring and parts fly off they don't get lost.
Clean the contacts with very fine sandpaper, points file, or even a course paper towel which worked for me. Since disassembling and cleaning the contacts I've had no trouble with AC.
Happy motoring,
©2002 Winston Fong
