Checked the vacuum canister and the lines in the engine compartment no leaks good vacuum. Checked the two check valves on manifold and going into the car where the AC tubes; both working. Where specifically does the hose entering through the firewall go to the vent controls / AC controls? basically, AC goes away on acceleration. Any ideas would be much appreciated,

 

Did you check all that stuff for vacuum under acceleration?

The problem is rarely behind the dash.
FWIW, the vacuum line goes to the heater control unit in the dash. from there, the vacuum is distributed to different components as selected.

 

What do you mean by the "ac goes away"? Does the airflow change from the dash vents to the defrost?

Do you still have the heater valve? Did you check that line as well?

 

Ooo this is something I actually have experience with. so as you know, the blend gates are vacuum actuated. My reservoir tank is gone, and when I'm on load the blend gates will close up. (helps that I don't have a dash, can see all this working!) Do you have any air coming through when on load? this would effect you any time your selector was set to anything other than heat or defrost (i.e. using your front vents). I know you said that you didn't think you had any leaks, but it sounds like you have plenty of vacuum to the controls, but it's not enough to keep the blend gates in the open condition.

To answer your question directly, there is a connection directly on the back of your climate control unit. this separates out to the vac lines at 3(?) actuators, selected by the vent control part, not the temperature control part.

If I've misread, and your blend gates are functioning correctly, then you probably have an AC issue, not a vacuum problem

 

Pulled the AC/Heater control and removed the rectangular insert that has all the small vacuum connections. The piece has a crack down the middle. replaced voila works.

 

Nice job!! You are now an expert.