01 Winn Journey air pump

Finally found the problem,after replacing the canister ,still kept running.took the dash apart,found nothing there.started digging around in the front compartment and sure enough there it was a dry rotted piece of tubing,cut out the bad part and works like a charm now.Once again the vast and unpaid research department came through with a lot of help.Thanks again jg

Vacuumm pump

I wrote Dorman about the size, reply was 156mm about 6-1/8 inches.

The Dorman is the only popular aftermarket tank. If it fits it's the one to get. Others start at about 3x the price, and a sphere is the perfect way to store vacuum or pressure.

Looks similar, the pump is electric,when I unplug the hose it runs continuously.Will look at it this morning.Thanks for the info. jg

If your chassis uses vacuum powered controls for your Heat/Ventilation/Air Conditioning (HVAC) system, then a Diesel probably uses an Electric Vacuum Pump to provide the vacuum for those controls. This is the most popular automotive vacuum reserve tank/reserve reservoir on the planet.
There are two models: Dorman 47076 has a built-in check valve. Purpose of check valve is to retain maximum vacuum in the reservoir if the source vacuum (which I think is a pump in your case) reduces or stops. This happens in gas engine vehicles when the throttle plate opens. Dorman 47077 has no check valve and at least with gas engines it needs an external check valve. If you have such a reservoir and it's cracked, one of the two Dorman models should fix your problem. 47076 has two connectors and 47077 has only one.
Your pump should run only occasionally. If it runs continuously or cycles often, something's leaking.
On gas engine vehicles, the problem is often BEFORE the actual HVAC control panel in the dashboard.