[Bruce Clarkson]

I just got a 68 Bonneville with the 400. I also got machine readable versions of the various service manuals. I'm trying to understand the misconnected and disconnected vacuum lines on this car. I see various diagrams of parts of the vacuum stuff in the manuals. Is there somewhere where there is a more comprehensive and overall diagram? For example, I see a diagram showing HVAC actuators, etc. but I don't understand where that vacuum comes from. Is it connected to the Vacuum thermal sensor that is on the front of the engine? (I'm not at all clear what that whole vacuum thermal business is all about.) Anyhow, an overall roadmap would be so useful in putting this car back the way it used to be. Perhaps I missed something in the manuals? Perhaps I need some additional publication I did not know about?

Thanks in advance,
Bruce Clarkson

[steve25]

The Termostatic vacuum system was used for emissions and to keep the motor from overheating.

In 68 all the motors be they in front of a auto or manual transmission had that TVS switch in the front of the intake.

[pfilean]

I don't have 68 manuals for reference but I suspect that the HVAC system is best referenced from the the HVAC specific manual. Generally that vacuum would be separate from the engine system and from a fairly small vacuum connection from the rear base of the carb or manifold. Engine vacuum needs won't care about the heater or AC.

[steve25]

If I recall right everything in the 68 HVAC system is controlled by cables other then 1 vacuum diaphragm, so only one full manifold vacuum source would be needed..

If you look closely at my second photo you will see a 2 port Tee at the rear base of the carb.
There’s one unused port seen there and that’s the vacuum source for the HVAC if I am not mistaken.

Sorry I should have noted this detail in my first reply.