Help with dash a/c-1994 georgie boy pursuit

[glamisorbust]

I have a 1994 georgie boy pursuit on the P30 chassis. I just got done replacing all of the dash a/c parts as follows:
expansion valve, receiver/dryer, a/c line, fittings, o-rings, switches, etc. Got it blowing ice cold which is awesome. What isn't so awesome is that under even medium throttle around town it blows straight to the defroster which ain't cooling me off at all. If you come back down to idle, the air starts blowing good again. On the highway, just going 55 mph, the engine has lost enough vacuum to make it blow on defrost the whole time. Has anyone had this exact problem, and what was the fix? I'm thinking it's a bad vacuum line or a check valve/vacuum ball. I have not ripped the whole thing apart yet to repair it, trying to get some ideas on where to look for the problem.

[PaulJ2]

Most likely looks like a coffee can or a round plastic ball type. I have seen them everywhere from on the firewall, the inner fender on the right and the left, and even behind the front bumper. Start by following vacuum hoses from the engine.

[Big_Katuna]

The RV maker places it so it moves around. You can test for leaks with WD 40; when the spray gets sucked into a cracked line the RPMs raise up.

[wny_pat1]

A picture is worth a thousand words.
https://www.google.com/search?hl=en&site=imghp&tbm=isch&source=hp&biw=1092&bih=514&q=Chevy+vacuum+ta...
One of the images in the above link should give you a very good idea of where and what to look for. My best guess is near the engine compartment fire wall.

[glamisorbust]

That still doesn't answer the question of where this thing actually is on the chassis, if there is one. I have looked all over, have seen nothing like it anywhere on my chassis. What would the vacuum lines hook up to?

[Big_Katuna]

Google " Chevy vacuum tank". Tap "images".

It could be the big round one or the coffee can.

[glamisorbust]

I looked all over the place, both under the hood and underneath on both sides. Nothing that resembles a coffee can. At this point I don't think this motorhome has one. I guess i'm gonna take the dash apart and replace every piece of vacuum line.

[havasu]

Biggish round sphere usually on the bulkhead on the drivers side.

Recognized by the vacuum line going to it. On my old 84 P30 I had replace every piece of vacuum pipe. It's hard to find in colors so I used black and remembered to label them 🙂

[glamisorbust]

Where exactly on the chassis is the vacuum can? I will replace it if need be.

[Big_Katuna]

I agree you have a leak somewhere. Inspect the vacuum can; coffee can looking thing. I have heard of people adding a small vacuum pump to run the dash stuff. My 97 GB Pursuit didn't do it even in the mountains under WOT.

[sch911]

"I'm thinking it's a bad vacuum line or a check valve/vacuum ball."

I would agree. The tank may be in the shape of a coffee can. They do rust out.

[Johno02]

Sounds like a vacuum line. put a gauge on the vacuum lines, if there is a leak ore bad line, it will also help the way the engine runs.