Acme Dash A/C vents not operating

[Jim Edwards]

Hi Looking for any info, diagrams, flow chart, etc. on the operation of the vents. I have fan, cold but cannot direct the vents to dash or defrost etc. Systems seem to be pneumatic. I would think vacuum. but source of vacuum? (or pressure). Driving down the road was working then not. !?!
 Any help would be greatly appreciated.

Thanks Jim

[Steve Huber Co-Admin]

Jim,
Your coach has a vacuum pump located under the front cap. (Diesels do not create vacuum so a pump is required for the climate control). It feeds a vacuum reservoir also located near the pump. Both should be accessible when the generator slide is out. However, before you dive into that, check the vacuum lines that hook up to the dash climate control unit. They normally are combined in a plug and this can come just loose enough to break the vacuum supply.
Steve

[Joel Ashley]

Steve's probably on the mark re. the vacuum.  But also check that the flex tubes under the dash are fully connected, as they can come unclamped over road time.  One time one of our tubes even became full of water from a hidden windshield or front cap leak, and the subsequent belly in the tube acted like an under-sink P-trap, so air couldn't flow.  Doesn't sound exactly like your intermittent symptoms, but easy to take a look.

Joel

[Jim Edwards]

Hi the final solution, was that the vacuum pump had failed in that burnt electrical way. It was a Hella pump that is no longer available. A replacement of similar configuration is a Dorman 904-214. Unfortunately the connector on the original is oval and the Dorman pump is round so a Dorman 645-740 Vacuum Pump Pigtail is required. The pigtail for some reason is 4 wire of which you only need two. Green is ground and black is power. (wires are NOT labeled) In diagnosis, it should be noted that the power to the vacuum pump is NOT connected directly to ignition power but is switched by the A/C control unit. So ignition key AND a/c fan must be ON to test power to the vacuum pump. As always this was the way it was done in my coach!