98 Ram truck has an issue with the ac system, when vacuum drops when accelerating up a hill for instance, the cold air in my face drops out and I get what feels like room temp air, possibly from the defrost vents, then comes back on cold in my face when I back out of gas. My actuators, and I think there are three of them, are the vacuum type not electric. Can anyone tell me by the description I gave which actuator it is and the location, or if it's an actuator problem at all, maybe a broken vacuum line somewhere? Thanks for any input.

It's been a very long time since I was up on this, but if memory serves there was a check valve known to fail on occasion. Neither of mine ever failed so no firsthand experience.

as i have had several early caravans, that problem surfaced on them as well.
it was in the control, plus a check valve.
i know you don't have a caravan, but are experiencing the same problem with a vacuum control as i did.
you may find something if you pull the control from the dash and check out the back side of it carefully, as well as the connecting hose assembly.
just my experience with the same problem, although on a different vehicle. actually, several in the 85-90 something year range.

You have two check valves, one right out the intake and another up by where the vac line goes into the cab) You can get replacements from napa.
https://www.napaonline.com/en/p/NDP7301349

There was a TSB in the late 1990s to remove the factory vacuum check valve and replace it with a little “vacuum tank check valve combination”

I had the blend door go bad on my 2001 (common issue), although your description sounds different than what I experienced.
I could hear an audible "thump" under the dash and would get an immediate blast of heat out of the vents.
Just something to consider as you're diagnosing yours...

There was a tsb (tsb 24-01-96) about the early second gens because they didn't have the second check valve but never hear of this one.

Thanks guys for your thoughts, I will begin to investigate. Is it possible at this late date to look up any TSBs anywhere?