I have the air control system for the air suspension I think. The bottom of the tree has one hose that goes to the dash heating/cooling controls. There is one hose loose and one nipple open, both blow air. If I connect the hose to the open nipple the dash air controls don't work.

See photos

Opps the second photo did not post, the end of this the unit is not hooked up to anything. Any suggestions?

That thing coming off the air manifold is first a air regulator and followed by a vacuum generator. It uses a venturi principle to generate a vacuum by passing air over a reduced orifice. Vacuum is needed to operate you dash HVAC controls and because diesels have no manifold vacuum, a source of vacuum is needed. When it is operating, you will hear a hiss of air coming out of the open nipple. It should cycle, if not, you have a vacuum leak or the unit is defective.



These vacuum generators work well but do fail and they are NLA, originally used in Ford diesels. Both of mine gave up and I replaced the front one with an electric vacuum pump and switch.

You will probably find another one back in or around the engine if you have a vacuum operated cruise control. When that one failed, I replaced the cruise control with and electronic unit from a GM 2500 pickup truck.

The thing that I did not like about these was that it uses a continual supply of air when generating vacuum which means that as you drive down the road, you air pressure will cycle up and down. These are supposed to be self regulating units and should shut off when a vacuum of a certain level is reached. Unfortunately, leaks in the vacuum system and use of vacuum, will use air.

That explains why the dash stops working when I block the open vents, I stop the venturi jet from working. Makes sense now! Thanks, and yes it does cycle the air pressure.

Hey, thanks for asking that question. I have been wondering what that thing is. I have also wondered where the A/C controls got their vacuum, as they appear to be stock GM vacuum operated of the era.

My vacuum does not cycle.

What are the chances that my cruise control is operated from vacuum? It is rock solid (both air pressure and speed.)

Is the Jake Brake operated from vacuum?

'96 Barth Regency 400hp Cummins M11.

quote:

What are the chances that my cruise control is operated from vacuum? It is rock solid (both air pressure and speed.)

Is the Jake Brake operated from vacuum?

'96 Barth Regency 400hp Cummins M11.

Chances are that yours may have an air pressure operated cruise control, they are MUCH better then the vacuum systems. Jakes are air pressure operated also.

the M11 uses engine braking and not exhaust braking. Don't often disagree with the wrench but I believe the M11 will have electric controls.