toofast928

Looking for some more room. If the Vacuum tank is removed does the HVAC still operate normally? Has anyone tried it?

dr bob

That reservoir supports the flappy on the intake, the HVAC diverters, and the cruise control servo (right there by the vacuum accumulator). Without the accumulator, the heater valve will open and the airflow will divert to the defrost vents on accelleration. Cruise will work so long as it doesn't ask much of the engine, to the point where intake pressure goes higher than what the cruise actuator needs. Flappy wouldn't work when you accellerate, pretty much the times you would want it to work. Also-- vacuum for tank vent diverter? Need to inspect the vacuum diagram more carefully.

You might decide to find a smaller one and put it someplace else, but I'm pretty sure you want to keep one someplace in the system.

toofast928

Well I only have one of the three Bob, the heater valve. Good point that it will open on acceleration.
Thanks

dr bob

All the HVAC actuators will go to their default positions when there is no vacuum. That's pretty much full hot to the defroster. Center and footwell vents close, fresh-air door closed. defrost vent and heater valve open.

What were you planning to put in that wheelhouse area? Not a whole lot of room there even without the bubble-bottle.

Tails

Dr Bob,
Totally agree with your assent as the vacuum tank is the same as an accumulator, in actual fact it is an accumulator at a perfect vacuum (zero pressure).

I have driven cars where the vacuum tank has been too small and under hard acceleration the vacuum actuated solenoid valves would change to default positions.

Excellent posts.

Tails 1990 928S4 Auto

FLYVMO

There are electric vacuum pumps you can install in lieu of the vacuum canister. JEGS sells them and probably Summit Racing as well. Here's a link: http://www.jegs.com/p/Comp-Cams/Comp...45586/10002/-1

Cheers!
Carl
90GT Project

Hold On

That vacuum pump is interesting. Would that solve my cruise control issue with low vac on my supercharged car. I could take the cruise and HVAC vac circuit completely away from the engine source?? hmmm any comments?

jpitman2

If its the specific space under the fender you need, just move the tank elsewhere. Or use a different style - there are many after market vac tanks around (round ended cylinders in steel), used for things like extra vacuum for trailer brakes etc.
jp 83 Euro S AT 54k

FLYVMO

I haven't tried it...yet, but from reading the manufacturer's instructions, it seems to be ideal for those instances you mentioned. Maybe someone on the list has first hand experience with this setup and can share some info?

Cheers!
Carl

GlenL

I've removed the tank and have the heater valve only and the HVAC circuit. I don't find it opening. The trick is to have an HVAC system that is sealed well and a good one-way valve up by the booster.

When I track the car I hold it at WOT for extended periods and never have I felt hot air gush out the vents.

Aloysius

I thought that w/o vacuum, if the heater valve is installed the correct way, the circulation of the coolant will keep the valve shut -> no heat. This would jive with GlenL's experience. Also, the vacuum take-off for the HVAC / Cruise and the bottle is from the brake booster IIRC, so is this affected by the engine / fuel vacuum system at all? I thought they were separate systems. . . . hmmmm. Someone set me straight - I have an 83, maybe it's different than what you're working on.

dr bob

The takeoff to the one-way valve is from the manifold side of the brake booster check valve. On my S4 that's manifold pressure minus whatever extra the little venturi booster can help. If the hvac is perfectly tight then no need for the accumulator.

PorKen

You could replace the external tank with a 78-79 door lock tank (19), which mounts inside, above the pedal assembly.

toofast928

Thanks Ken I was thinking the same thing.
Bob I was pondering installing an electric power steering pump in the cavity. Little tight in front of the engine mounting the Pro-Vent, Fuel Cooler Can, and Electric PS.
Tony

GlenL

That's what happened to mine. The oil/air separator/catch can sits in the fenderwell instead of vacuum can and cruise control servo. A few spare holes in the fender wall made it easy.