vacuum reservoir for heater/defroster controls

[FOOSE]

Hello,

I'm wondering if I need the vacuum reservoir for my heater controls? its a big ugly ball and it sure doesn't look good under the hood of a custom engine bay. could I just go straight off the intake or what kind of problems would I run into?

Thanks a bunch!

[Jason S]

If you have the vacuum operated controls in the cab, such as what came on a factory air truck, then you will need the reservoir.

You could hook up the controls straight to the manifold, but when the engine vacuum drops (i.e., wide open throttle or chugging up a long hill), the heater/defroster doors under the dash may change positions.

[FOOSE]

Hmm yeah that makes sense...do you know how big of a reservoir I may need? I don't want the factory bubble type. I was thinking about making one with a piece of 2.5" stainless steel exhaust pipe and custom TIG weld it shut. maybe 7 inches long. it would give me 25 cubic inches. does that sound like it could work? I have no idea how many cubes that factory ones are.

[Jason S]

I didn't measure the actual diameter of the spherical reservoir; but if it is a 4-inch diameter sphere, then the volume would be somewhere around 33.5 cubic inches.  So your fabricated reservoir would probably be adequate. 

You might also consider relocating the factory reservoir up under the dash (route the vacuum line into the cab) or use a reservoir from another brand car/truck and mount it under the hood or under the dash.

[FOOSE]

Yeah that could work, i'll have to check how much room is left under the dashboard.

It wouldn't by any chance just work to put a check valve between the line so I wouldn't lose my vacuum under low vacuum circumstances would it? without a reservoir then. I don't know its just a thought.

[werewolfx13]

You'll need a reservoir for reliable operation. I made one I used for awhile on my '83 c10 out of two 3" sch. 40 pvc caps and a piece of pipe cut just long enough for the caps to fit snugly, short enough for the caps to be touching. Sealed it shut, drilled and tapped it for 1/4" pipe thread, screwed a nipple into it,and adapted from that as needed. Just make sure you put a check valve on the engine side of the canister. I left mine loose in the glove compartment while I was using it, as it was just for function, but went back to the OEM ball type when I pulled one off my parts truck. Performance was the same, I just wanted my glove compartment back.

[Jason S]

It wouldn't by any chance just work to put a check valve between the line so I wouldn't lose my vacuum under low vacuum circumstances would it? without a reservoir then. I don't know its just a thought.

My $0.02, you'll want to have some sort of reservoir...  Whether it is the factory reservoir, constructed like werewolfx13's or swapped in coffee can reservoir from another make, you will be better off putting one somewhere.