M113fan

My turn with center vent misbehaviors. '02 SL500. The red and blue buttons light up but no air flows. Ran the diagnostics and everything was normal except item #64, Vacuum actuator 47 feedback potentiometer Volts, which came back at 0.9, while the left and right came in at 4.2 and 4.3, respectively. The center knurled wheel volts did range from 4.1 to 0.8.

None of the three knurled knobs have any effect. I pulled the codes and found three in the temp memory: 416, 417, and 419.

The CCU itself is coded to 00P.

I'm not sure where to look next, I found this schematic (http://manual.startekinfo.com/manual/JSP/cc/3_8/m31.jsp) but also a reference to something under the dash behind a trim panel. In that schematic it looks like that whole assembly is under the hood? I checked the vacuum line block under the hood and all the lines were attached and snug.

Thanks all!

M113fan

Update, I found a reference that my car should be coded to 03P so I made that adjustment but no change in any of the symptoms described previously.

M113fan

Update #2: fixed! Turned out there's another vacuum line right behind the center of the engine which goes straight to the bulkhead. The hard white plastic line has little barbs and sets in a rubber coupling. Mine had pulled out. So put it back together and bingo, everything works again.

Victory!

M113fan

REDUX: oddly, the little white nylon line had pulled out of its rubber hose in the engine compartment again this morning. I'm not sure what has happened to cause its available length to be reduced, the nylon doesn't look to be broken and still has the little formed barb at the end. I've built a tiny extension using spare vacuum hose and fittings I had in my parts bin, but it is something of a mystery.

mahunt

It sounds like something isn't routed like it was originally.

M113fan

I think that's probably true but the question is why, or how? That bulkhead is a *long* way from the in-cabin visible fixtures of the dash, and as far as I know, the vacuum lines don't route to the CCU itself, only to the valves.

My workaround seems to be working fine today but it's still odd.