ISSUE IS FIXED !!!

THANKS  FOR YOUR THOUGHTS. 

1975 Corvette Roadster 

Engine:  350 / 330 Gen 1

Problem 1:

Headlights don't  open & close.  Engine vacuum 19 reading normal range.

Action taken:

Checked vacuum hoses under hood found headlight vacuum relays and canister seals leaking, replaced all with new.

Results:

Headlights function as good if not better than factory new!

Problem 2: (Requested assistance from C3vette registry forum)

Interior air / heat system actuators not functioning properly. Doors not opening.

Found the "factory" vacuum supply hose from the engine compartment side  "check valve" compromised inches from the firewall inside the cab.

Action taken:

Replaced with new vacuum hose.

Results:

System functioning OK now.

* Thank you all for your helpful comments. I hope this helps other who may have similiar issues with their C3.

Start at your source vacuum (engine) and test from there using a gage or at the actuators and move back to the engine.

Remember the lines go into the switch as well. Test where you have vacuum and see if it is routing of hoses, or component failure causing issues with lower vacuum reading.

Keep Us posted👍

There are actuators under the dash and up inside the side panels.  The actuators could have developed a leak.  Once you locate them you can check them with a hand held vacuum pump. 

Or that rotary vacuum selector valve that is hooked up to the HVAC control on the console is leaking.

Thanks!

Phil,

In the future, please do not remove the text from your original post.  It should be left there so that people can learn from whatever your issue was and the recommendations that follow.  Posting a reply to say it is fixed is helpful, and maybe detail on what was done to fix it.