HVAC Vacuum Reservoir???

[First c10]

I searched and could not find an anwser, so thought I would ask the question.

Do you have to use the stock Vacuum reservoir for the HVAC?
and if so can it be mounted under the dash?

Thanks
Scott

FYI
1970 C10 CST with factory AC LC9/6L80E

[JimKshortstep4x4]

You don't have to use the factory vacuum reservoir and you can mount it under the dash. You will want to use a good canister that is made for vacuum and is at least as large as the truck unit.

Jim

[First c10]

So you have to use a canister???

[JimKshortstep4x4]

I did not mean to throw you with the terminology! Plastic or metal can be used as long as the part is made for vacuum.

Jim

[First c10]

Jim so you HAVE to use a canister? As in a canister is needed and will not work and will NOT work without it?

[68c10airstream]

Hi firstc10, I went to auto schooling in the 70's and remember the vac tank well. It's purpose is to check and hold vacuum, because when you step on the gas manifold vacuum drops off, and the vacuum that was in the lines would be bled off into the intake and there would be no vacuum available. 2 lines hook up to the tank, engine supply, and the other line goes to the controls inside the cab. It can be hooked up wrong (backwards), so here is the test. Use 2 vacuum hoses, install them on the tank, put your finger over the open end of one line from the tank, then suck on the other line that is hooked to the tank. When you release the vacuum that you put on the hose, there should still be vacuum present on the hose that your finger is on. Another words you are acting like the engine would with vacuum present, then bled off, but there should still be vacuum remaining on the other line. Good luck, Brian Fuller

[68c10airstream]

I believe classicparts.com has that tank very reasonably priced. It mounted on the engine side of the evaporator housing in the engine compartment. 2 screws were used to mount the vac tank ball.

[First c10]

Thank you for the explanation would I still have a vacuum problem with a stock 2011 LC9? I was wondering if I could just eliminate the reservoir all together. If I need to keep it where is the best place to get vacuum from? Maybe I need to ask in the lsx area.

[piecesparts]

The reservoir is an important piece for your controls in the cab of a vehicle. It holds enough vacuum in reserve, to make up for those moments when your engine does not make good vacuum. This keeps the heating and air conditioning dampers from cycling to a different position, when the vacuum signal drops from the engine while climbing a hill or driving in heavy traffic. The newer vehicles have electronic controls on a lot of their dampers and controls and do not require as much vacuum as the older vehicles used to. If nothing else, put the reservoir under your floorboard to keep the volume of your vacuum available but the reservoir is out of site.

[First c10]

Perfect thank you.

[68c10airstream]

Hi firstc10, as far as an available vacuum port on an ls goes, i know my 2001 5.3 has a unused port on the intake. If nothing is available, dodge, plymouth, and chrysler, into almost 2000's had a spare port that was capped off right at the vacuum line at the brake booster. The thick vacuum line went from the engine to this round check valve assy, and that pushed into the booster. The capped off line was used for cruise control, hence this is your vacuum supply and check valve all in one. You could install this check valve in place of the gm check valve (if it fits) you would not need to get a vacuum tank and add it to the vehicle. I hope i'm not confusing you in the process, but if the check valve fits it would be a clean install with minimal sized parts only needing the vacuum line from inside the cab to plug into the check valve at the booster. If you care to venture into this, take your old check valve out and go to a junk yard with this post printed in hand and i think they would help you. Good luck, Brian Fuller

[First c10]

I used the 1/2" port on the back of the intake that was for the brake booster. I put a tee to the vacuum reservoir and to the brake booster. So far so good.
Thanks for all the input guys.