Heat and A/C control vacuum leak fix DIY

[gizwiz]

After troubleshooting my control unit with a Mityvac and a lot of beard scratching, I concluded two things: The black hose that feeds the vacuum motor that controls the airflow to the rear seat had a leak somewhere. I couldn't locate that particular motor, so I plugged the hose. The folks in the back seat can have a blanket. But there was still a leak in the controls.

With the unit out I it's possible to investigate all the stuff on the backside. And there is a lot of stuff there - I really didn't want to have to take it apart. But I found that there were five different vacuum valves that the hoses led to. One of them, connected to the right hand knob, was the easiest to get to. It's the thing with the blue (and other) hoses leading to it here:



It looks like there's a hose missing, but that's a vent there by design. Anyway, this one is acessible so i was able to get it out. The backside looks like this:



Notice the four plastic "hooks" holding the sandwich together. By deflecting these hooks it's possible to separate the parts.
For example, the valve that I suspected as being the leakiest is connected to the center fan switch knob. The backside of it looks like this, it's on a metal bracket with a BMW sticker on it, standing off at a 90 degree angle to the panel itself:




Although I was reluctant to try to get this off like I had the other, I had access to two of the plastic hooks that held it together. You can see them in this photo:




By prying the hooks and separating the assembly, I was able to slide a strip cut from a business card into the gap created, once it was slathered with vacuum grease (any silicone grease will do):




Plunging it in and out a few times slimed up the sliding valve parts so that once they were snapped back together it worked like new.

I've no idea if later e23 models had these or anything similar, but if Behr made them, it's likely.
My car is all back together now and it's great to hear the "whoosh - thunk" of the flappers doing their thing again.

[Hit Man X]

PM me your email. I have a bunch of files I scanned for that very early HVAC system.