Where is my vacuum pump?

[tony6373]

I have a '85 270 Isuzu diesel and the manuel says there are vacuum pump(s) where required. I spent a whole day crawling around under the M/H and never found a single thing that looks like a vacuum pump to me. Tried following lines but they all seem to go under or over something and disappear. The vacuum operated entry step has been replaced by a modern electric step. All four air bags are holding pressure at least for a few hours, I'm still watching that. There are various air or vacuum lines that are disconnected and just hanging and I don't know what they used to do? Also there is no power to the air compressor but when I hot wire it back to the battery it runs and fills the rear air bags.

Thanks for listening,

[Smartstream]

Originally Posted by tony6373

I have a '85 270 Isuzu diesel and the manuel says there are vacuum pump(s) where required. I spent a whole day crawling around under the M/H and never found a single thing that looks like a vacuum pump to me. Tried following lines but they all seem to go under or over something and disappear. The vacuum operated entry step has been replaced by a modern electric step. All four air bags are holding pressure at least for a few hours, I'm still watching that. There are various air or vacuum lines that are disconnected and just hanging and I don't know what they used to do? Also there is no power to the air compressor but when I hot wire it back to the battery it runs and fills the rear air bags.

Thanks for listening,

High Tony, your vacuum pump is mounted on the rear of the alternator. I'm not sure about your year but some of your heater/dash air controls may be vacuum operated along with the cruise control.

There should be a pressure switch that provides 12 volts to your air compressor when the air tank pressure drops below about 80 psi. and shuts the compressor off when the tank reaches about 100 psi. The compressor amperage draw is pretty high for the fuse in the fuse block so many of us have installed a heavy relay or solenoid with a heavy wire directly from the battery to the compressor. The fused wire from the ignition is now used to energize the relay/solenoid. This provides a good 12 volts to the compressor and takes a big load off the ignition switch and fuse block. This is the case on the earlier motor homes. I would guess it is the same on your '85 but Airstream or previous owners may have done strange things.

Good luck.

[overlander63]

There will probably be two oil lines going to the vacuum pump as well. Be careful removing those.

[shepherd57]

Dan

Where is the vacuum tank located I can't seem to find one on my 85 32.5. All I can find is a couple of black round plastic globes that look like they could have something to do with vacuum. Looks like the PO has disconnected a bunch of things. I can't even find vacuum hoses.

John

[tony6373]

Those round plastic globes ARE the vacuum tanks. In my case one is located aft of the engine and toward the curb side just barely visible from the doghouse. I think there is another under the dash.

Thanks to all who posted.

[Smartstream]

This is where the difference between years gets interesting. On my '82 all the controls are mechanical. Now that the original cruise control is gone, the only thing vacuum operated is the step. I have no tank, the hose goes directly from the vacuum pump to the step. You guys with newer coaches have all the vacuum spaghetti under the dash and the head aches that go along with it. I don't know when the change took place but I think it was '83 or '84.

[shepherd57]

Dose anyone know if there is a schematic of how the vacuum lines are run on these coaches with the Isuzu diesel