Attn jb

If you have no vacuum to the valve look for a leak in the system there is a vsv (vacuum switching valve) behind the right side console kick panel. If
you have vac to the vsv then the valve may be bad if not, then check the supply line from the vacuum source. Follow the vac lines from the motror to the affected area. Before you spend any money on a cc push button unit. Jo
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OK, no vacuum at defrost valve. I do have vacuum at the column of switches in center console behind climate control unit - 14 Hg on vacuum acording to my vacuum pump guage. one vacuum line goes to switch 1 (the top), teh otehr to switch 3. I put a used cc unit on it recently, but defrost didn't switch before i changed it either. Has never worked in the 10 years we have owned car.
1985 500sel AMG.

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