The beautiful, light touch climate control system in my 91 740 seems to be loosing its mind. Some days I get A/C, others not. Some days, the blower fan works, others not. Sometimes the air doesn't appear to go anywhere, other days it works fine. Do I have a circuit board taking a dive, or is there something else? (Mechanical side of the system has been checked, fully charged a/c, engine compartment switches and sensors seem ok and functioning.) If there is a board to be replaced, what's the trick to getting at it? I've been searching for a manual covering the later 700 series cars, but there doesn't seem to be one available. Any suggestions?