On my 1985 300D when I turn the thermostat wheel to heat I get plenty of warm air however I also hear a vacuum sound and the car will not shut off normally (like when you have a loss of vacuum). When I turn the thermostat wheel back to cool I get cold air and the engine turns off normally. I am thinking the problem is one of the switch over valves but which one? Thanks.

First, the only thing I've done with a 300D CCS is pull the dash and put it in my garage rafters after going 'holy crap, thats a lot of vacuum hose'.

My observation is that there's vacuum servos which tend to wear with age, and vacuum hose which is fine after 35 years. My bet is it's a leaky vacuum pod, and if there is a fresh air / hot air flap in the heater box, it's that one, the one inside everything.

Until things go more seriously wrong, you might put it back on cold air before shutting down.

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more likely to

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have an accident

two things

when you're on

at the same time.

a cell phone.

www.kiva.org It's not like there's anything wrong with feeling good, is there?

Sounds like the diverter flap that switches between air through the heater core and footwell vents vs. the a/c center vents.

On the W126, its control pod is located behind center console kick panel, driver's side.

There is a good optical function test in the FSM that helps to trouble shoot. (search "source FSM")