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I had air coming out of all vents on the Ac or Heat. It was suggested that it is the vacuum supply line coming from the back of the manifold that is the culprit - Because Battery Acid Leaks on it and it burns through. Well this is what happened or perhaps just it was rubbing and rubbed through thus allowing "NO" vacuum to get to the HVAC Vacuum manifold. (It did not have any Acid residue on it at all).
This vacuum line is "HARD" plastic and not easy to locate WHY? because it is within the wire loom going down to the area behind the passenger front wheel that goes to the PCM.

To Begin:
I had to jack up the front end of the Vette and turn the wheel all the way to the left, so I could remove the panel to access the area by the PCM and Vacuum junction One Way Check Valve.
You "WILL" need to take all the 7mm nuts off the panel (The ones underneath too) AND the last one for the fender on the bottom furthest toward the rear of the Vette right next to the door! This is because you will need to pull a little on the fender panel there to help see and work on the vacuum junction. Here is the culprit fully pulled out: I tested it by capping the end after I removed it from the back of the manifold, it held "NO" vacuum at all- I mean I could blow through it and inhale through the line even though it was capped off on one end!


Damaged area:


It is not hard to get your hand behind the manifold with the Valve cover/coil covers off , plus make sure you unclip the MAP sensor it makes it a little easier too get your hand on the vacuum line- I pulled the rubber end of the line off the fitting in the back (there are only two fittings on the back for vacuum) One for the Brake BOOSTER and one for the HVAC Unit


After it was all traced out and I found the end in the fender well - It ran into a oneway check valve: (Pic) The line on the bottom comes from the manifold and the other two - One goes to the canister right above and the other goes into the Vette's Cabin to the HVAC vacuum block.


With it pulled off:

The bottom goes to the manifold (vacuum supply) the one off the side goes to the Canister above and the one in the middle (top) goes into the cabin area.

Next I re-routed the new vacuum line to the unit using 3/16" fuel/vacuum line: Plugged it into the Manifold and routed it behind the battery down to the canister area-



All tucked in:

Remember to re-plug in the MAP sensor

Next I went to the fender area and tested "ALL" the lines off the One-Way Vacuum Check Valve (Using my mighty Vac): Tested to 20 PSI, the only one that did not hold was the direct line to the manifold:


I went ahead and replaced the small 90* vacuum line to the canister for a just in case since it was easy enough(You never know) :



Now After that was done I went into the Vette and removed the floor mat, the panel covering the BCM (Computer) and the upper kick panel - now make sure you pop the foot well light out of the upper panel so you can remove the whole thing and have a free open area to work (YEAH! Like there is a lot of room anyway - all twisted on my back crunched in that little area- Stinking crazy! )

Here is a shot of the line coming into the cabin area from the fender: They are kind of a hard to see but they are the two (One from the manifold and one from the check valve to the cabin) there in the back ground right above the PCM:


Now I tested the line from the fender to the cabin, here is a shot inside the Vette - The Black plastic line from the One-Way Check Valve couples into a "PURPLE" Line : As seen in pictures
Black plastic supply line: Seen at finger point


Pulled down a little to see the coupler: Black into Purple


A few pics of all the pretty colored vacuum lines from the vacuum block: (And to think I was getting no vacuum to this bad boy )



Next I pulled the Black to Purple Couple apart for testing and capped it off: Held very good at 20 PSI of vacuum for a sustained period of time:


I also tested the vacuum block and it held too. I was glad the supply line was good because I did not want to punch a hole in the firewall to install a 3/16" vacuum line, So I was able to use the factory one.Since it was good at this point I buttoned up the inside and put it all back together - even the floor mat - no really I did! Now back outside to the fender area where I re-assembled the One-Way Check Valve: Here are a few pics installed




At this point you can put everything back to factory - the fender screw and the panel screws and snug them all down - Lower the Vette back on the ground and make sure nothing was left off and no extra parts! AGAIN: Make sure you clipped the MAP sensor wire back in - because you needed to pull it off for easy access to the vacuum fitting on the back of the manifold - You did put it back on right!

Well now it is time for the test: Fire up - Turn on AC - Try different Modes - ALL WORKS GREAT - It's a cold party in here