Thermovalve in CIS system???

I've been looking at the vacuum schematic for the 74-83 CIS system. Between the vacuum limiter and the warm up regulator there is a device called a thermovalve. Can anybody tell me what this thing is supposed to do, and how I can test whether or not it is doing it?

Thanks



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Bill Krause
'79 911SC Euro

Methinks that is the vacuum valve that controls the vacuum to the warmup regulator. It is open when cold, so on a cold start, it allows vacuum to the "vacuum controlled" warmup regulator for initial enrichment. It has an electrical heating element that warms with the ignition on. After about 30 seconds, it has warmed up and closes off the vacuum to the WUR. The WUR continues to warm itself up through its own electrical heater as the engine goes through its warmup period.

Thanks, that makes sense. My WUR has two vacuum hoses attached to it. One that goes directly to the throttle body, and one that passes through that thermovalve thing. My Bosch book has a picture of a similar WUR, but doesn't explain why there are two vacuum inputs, and doesn't describe any vacuum induced enrichment during warm up. I think I'll pinch off the one from the thermovalve and see if it makes a difference when starting cold.

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Bill Krause
'79 911SC Euro

The vacuum line thru the thermovalve should go into the bottom of the WUR. During the 30 seconds that it operates, it richens the mixture only during the very early period after startup. That's 30 second MAX at very cold temperatures. Up around 60 or so degrees, the thermovalve is closed BEFORE starting, so there it no initial enrichment.

The other vacuum line operates to lean the mixture at high vacuum (throttle closed) and richen the mixture at low vacuum (throttle open). Thus "vacuum-controlled WUR".

The two vacuum lines work against each other. The one that goes thru the thermovalve operates over a larger area and overpowers the line that comes in the top of the WUR. But it only operates for <=30 seconds.

Thanks, that was a great description.

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Bill Krause
'79 911SC Euro