On my 1997 BMW 328is, the A/C works whenever it wants!! (on and off)

I had a similar issue with my '96 328i. The buttons on the climate control worked, but no air blowing through the vents. It turned out to be the Final Stage Unit a.k.a. Blower Motor Resistor. Found one online at SoCal Motorsports for about $75 bucks. Local dealer wanted $135. Do the math. ha ha. Here is a link to DIY http://forums.bimmerforums.com/forum/showthread.php?p=3349096 Hope this helps.

wow my car is doing the exact same thing! same year and model and does the same thing. found out its a chip fried iside the panel... $600 to fix or find a whole new panel for 120. so yeah.

In my case it was a card that went bad. An electromechanic put a bridge on the fuse box to avoid spending 200 bucks on a new card.

you need a final stage resistor.replace it yourself.u can access it to the left of the passengers footwell.probably need to remove the glovebox or at least the lower panels.

Typically it's the blower motor regulator. I've ran across it on a Mercedes I owned but not one (of the eight) BMWs I've had. It's usually mounted to the blower motor and located either under the glove box or between the firewall and center console depending on the design. The regulator has a heat sink on it to help cool the regulator. Over time they fail or function periodically because it will overheat sooner than normal.

can be the compressor clutch failing..

can be the fan speed resistor........if the climate controll display-unit in the dash goes on and off, you have to re-solder the little blue capasitor inside the unit on the pc-board. on the right-hand drive cars the fan resistor sits behind the cabby-hole!