A/C switch broken

[yonatan11]

A bit of a funny story. Me and my brother were driving back from a football game in our prized 1991 bmw 318i, when suddenly our windows stopped working. One was down, and driving on the interstate with 1 window down is a headache so we decided to pull over and replace the fuse. We didn't have a spare one and since it was a clear, blue, sunny day we decided to temporarily swap the windshield wiper fuse for the blown window fuse.. Problem solved! woohoo! Not so much. We roll the windows up and continue on our way. It's getting pretty hot so we try turn on the A/C.. doh! A/C doesn't work now! So we roll down the windows and the window fuse blows again. Once we replaced the window fuse with a new one the windows have worked fine and no blown fuses since then, BUT, the A/C doesn't work now. The fuse in the A/C is fine, so i'm guessing something with the wires? Perhaps it's just the switch?

Anyways, sorry for the longwinded story but I figured that the series of events may have had something to do with it

Any help would be aaawesome as i'm in Louisiana and it is starting to get hot hot hot

[romeomike]

Blown power window fuses (#17 @ 30A) generally are due to shorts in the wiring, or someone putting in a fuse of the wrong capacity (as I've observed in other threads on this issue).

I have a 1991 318i as well, and recently went through an extended AC troubleshooting session on a 1990 325iC.

An AC pressure gauge would be very useful to see if you have enough refrigerant in the system to at least engage the compressor clutch. I'd do this test first. Not enough or too much pressure at the refrigerant pressure switch = AC won't cycle. Once that's eliminated as a cause...

1. If you look around on the Internet, you can download the Electrical Troubleshooting Manual (ETM). The one for our model year is a bit small at 6MB, while the 90 convertible is about 16MB. In the ETM is an extended series of tests you can run that don't require you to evacuate the refrigerant from your system. A digital voltmeter will come in handy.

2. There is an E30 factory repair manual (around 100 MB) -- search for Bentley-boembi.rar.

3. There is an E36 pdf version of the Bentley repair manual out there, because the Bentley BMW 3-series manual doesn't cover the M42 model year.

The main fuse for the AC is 20 (30A). Back when I was having troubles (that unfortunately weren't cured until I replaced the compressor), when I cycled the AC, fuse 19 (7.5A) would blow as well.

There's a small black AC diode (1-3/4 inches long) underneath your fuse box. With a voltmeter in diode test mode, place the red positive lead on the male spade terminal and the black negative lead on the female -- you should get a reading other than 1 or OL (out of limits). Reversing the test leads should yield a 1 or OL if the diode is good. From looking at the ETM schematic, if the auxiliary fan runs when you press in the AC switch, the diode is probably OK (as well as fuse #3 and the K1 relay).

If you have a salvage yard nearby, you might get fortunate with parts or a BMW to practice on.

Good luck -- we're all counting on you (Airplane!)