C3 Vacuum heater controls

[Jack O.]

On my '69 (no A/C), when I shut down the engine with the heater control in the off position and the other control on int the C (Cold) position, I hear air escaping - like a vacuum leak. Is this normal - for example, once the engine is shut down and no longer providing vacuum, the air control door returns to an open position and thereby forces air out of the vacuum controller or some such thing which is what I'm hearing? Or do I possibly have a true vacuum leak. I recently reassembled everything and believe its all sealed up good.

Thanks.

[Geoff C.]

Re: C3 Vacuum heater controls

You have a leak. Probably in the rotary valve, if not the rubber hoses. They can be taken apart and repaired, but also can be had new. It's a budget and/or time decision to repair or replace. Some jobs are better done just once, because they are a PIA to repeat.

Geoffrey Coenen

[Jack O.]

Re: C3 Vacuum heater controls

But it sounds like the escaping air is coming from up under the dash rather than at the controls (I have it pretty well apart). I take it from your answer you do not think my hypothesis, i.e. a normal leak down after engine shut off, is viable?

Thanks for the help.

[Geoff C.]

Re: C3 Vacuum heater controls

I missed your point about the leak coming from behind the dash. I do not believe a discernable vacuum leak down at engine shut off is appropriate. A tell tale symptom of significant C3 vacuum loss is the head lamp or wiper door popping open on their own or a climate control vent/blend door moving. This usually signifies there is a leak somewhere in the network: hoses, actuators or switches. Troubleshoot each individual component and hose separately to isolate the source.

Geoffrey Coenen