Tom, both of my vans ac systems work flawlessly regardless of engine speed. 80mph on the highway driving uphill in the ozarks it works great. At an idle still works great! I can turn the **** and the adjustments are as expected. I bypassed the vacuum canister.
You have to do whatever you are comfortable with. Me i had the supplies on hand. So that's what it got. I may have been ribbing others about the canister being an evolutionary thing like an appendix. And that stems from my fondness of the 7.3 powerplant. And thats ok too. Again you have to make your repairs as you see fit.

 

dieseldogtom,
Can and reservoir are the same (mean the same thing to the car). The can reference is from the 70's and 80's when they used a soup can looking metal can
IMHO you need no can (reservoir) with a vacuum pump that functions properly (as long as it works and the engine is running you have good vacuum)
The can is there from the factory IMHO possibly just to get the sobs out of warranty with no problems. ha ha (they do not want to have to replace a weak vacuum pump under warranty)( only sourced from Great Brittan)
You start pumping the brakes on an old 6.9 with a vacuum brake booster and you will quickly know why the can is there (hard brake pedal after about 3 pumps)
I have not had the pleasure to replace a can on my or any van yet (thank God) and if engine removal is needed then for sure find a place for a new can or delete it and hope for the best
If you continue to have trouble with this after all the can bullchit you had better check the vacuum mode switch for supply and proper function (sometimes the mode switch itself leaks and you get defrost heat or panel only)

 

Weather warmed up enough to replace the VACUUM line ONLY (well a check valve on it too).
System works just like it's supposed to under all conditions.
For clarification purposes only.. I separated out the words Reservoir & Can because
I consider the vacuum (container) a "Reservoir". I consider the mechanical operating
devices that control the arms that move the flap positions "Cans" Because THEY are ACTUALLY
shaped like cans AND are made of a metal material.
My (ISSUE) I already diagnosed was/is not with the selector switch. (I'm stupid but not that much).
Anyway, I choose to run my new length of vacuum line down on the passenger side but as some
know it's not an easy area to run anything through from engine side to interior floor area side.
I decided to just feed it through where the Radio antenna wire went through which is not being used anyway.
Fairly easy access area and nice rubber grommet already there once I pulled antenna wire out.
All works as it should. Just for fun I tried to use my little endoscope device to see if I could get a glimps
of the mysterious hidden reservoir. Didn't matter what hole I stuck the thing into I never could get a glimps
of it. I don't believe it's really there!!!!!!! LOL But who cares because it's USELESS when ya got a vacuum
pump.
This is my last post on this subject. Just wanted to follow up with another confirmation to anyone that might
be interested that all works well WITHOUT the reservoir And if "the pros" would never repair it without
installing a reservoir back to OEM, That explains why so many of (us) avoid "the pros" like the plague!
I don't need everything brought back to OEM conditions & I sure don't need to pay the extra labor hours
it would take to do so. I just want it to work again, And it does! And frankly, I don't want to spend the extra hours
to OEM it back either. I read the post where one of you cut into the wheel well area to access the OEM reservoir
& R&R it and then do a patch job on the hole. While that's all well & good to at least prove the thing is there! LOL
I would never go to that length for something like this. If you absolutely feel you need the thing just do the
relocation job. But for those that might be reading this in the future that are having this decision to make as I did,
Just run a new vacuum line & forget the reservoir. It works just fine.