Vacuum for DIesel Pusher LY

[Paul Dobbin]

Vacuum for Dash A/C

On our Diesel Land Yacht, the following occurs:
With Dash A/C on, all the vacuum operated dampers default to blow the air only through the defroster vents.
I assume that the controller is a Chrysler product with this as a default setting that happens when there is a lack of good vacuum.
Questions:
1. If my assumption is correct, What is the source of Vacuum for the Diesel.
I always thought Diesels had low vacuum and needed a vacuum pump.
2. If so, where is it?
3. Has anybody else had this problem?
4. My manuals have nothing on this. Is there a better manual?
Thanks for you input.

[overlander63]

Paul, you may just have a broken vacuum hose going into the dash, most vacuum-controlled ductwork defaults to the "defrost" setting when it has no vacuum.

There will be a vacuum pump on the engine somewhere, if it is an Isuzu engine, the vacuum pump should be mounted on the rear of the alternator, and they do go bad.

[Paul Dobbin]

Originally Posted by argosy20

Paul, you may just have a broken vacuum hose going into the dash, most vacuum-controlled ductwork defaults to the "defrost" setting when it has no vacuum.

There will be a vacuum pump on the engine somewhere, if it is an Isuzu engine, the vacuum pump should be mounted on the rear of the alternator, and they do go bad.

Thanks, I'll start there. The Airstream has diesel engine is a Cummins 230 (used in all Chrysler trucks) I'm hoping it uses the same vacuum pump as the Chrysler,
if so I should be able to get it at any auto parts store.

[Tom Nugler]

Hi, Paul. You're on the right track. In addition to the vacuum pump on the engine there is probably a vacuum reservoir hiding somewhere in the engine compartment. (Yes, a place to hold nothing.) These are always a prime source for leaks, split hoses, and bad check valves. I'm not too familiar the this product, but it can look like anything from coffee can to any other piece of injected molded plastic hanging around in a modern engine compartment. Just try to follow the main hose off the pump.
Good Luck, Tom.

[Paul Dobbin]

The Answer:
As most carburation problems turn out to be electrical, so did this vacuum problem.
After looking all over the engine compartment (in rear/diesel pusher) for the vacuum pump, even had a picture of one from the parts store, I started at the front of the coach. I thought if I took the temp. regulator out I could track the big vacuum line back to the pump. In the process I found the vacuum pump right behind the left headlight, under the front bonnet. It's an electric pump!!!
When I started the coach, the pump did not run (now that I knew where it was) so I then knew why I had no vacuum.
Next step, Why no pump? So I tracted the wire and before I could find my meter to measure the electric current to the pump, I found a loose connection at the master electric board. Connection repaired and all the A/C functions worked by vacuum work perfectly. So does the dash A/C.
YEAH !!!
So some days it's better to be lucky than good, this was one of those days.
Thanks for all the input. Does anybody have a source for a good Sparton/ Airstream Land Yacht find/repair manual.