Hi- I have a 2001 DRM 3500 5.9L.
I just took off on a road trip from Fl. to Ca.. My AC system was largely rebuilt recently and ice cold working great in the "flatlands" of S. Fl. for a month. No work needed to be done on the blower but getting into some large hills (not mountains) the fan is cutting out under very specific conditions. I "goose it" for better gas mileage from like 60 to 70 going into the base of these moderately steep inclines and slowly slow back down to 60 or so going uphill. Sometimes I'll have my cruise control set for that 60 but not always. In either case when I reach that speed I maintain it to the top and by experience know right at that point (hold speed at 60) the tranny almost "wants to" kick down but doesn't quite need to. At this 60 mph point sometimes the blower quits at any fan speed including high- never any other condition. So far I don't know if the compressor has also disengaged but could figure that out if I need to.
No big deal so far with fan always restarting (instant cold on restart) after maybe the 15 seconds at most it takes to the top of the higher hills. I'm heading into a "heat wave" and real mountains in a day or so and would appreciate any ideas here.
Thanks.

 

Question becomes, is the fan actually stopping, or are the vents simply switching to defrost? (default position when there is insufficient vacuum.....)

 

I see what you're asking. I'm not in hills now but when I get back in them I'll check. Defrost makes quite a different sound and of course I'll just feel for air there.
I only use 1st AC dial setting (max AC) and when I do feel the the air come back it's on my feet first than like 2 seconds later out of the dash vents. I noticed this sequence occurs whenever I first turn the AC on AND when I switch from defrost to max AC. This van throws 1 code (PO441 I think) for small vacuum leak.
Thanks HeyYou- I'll get back after checking defroster

 

The code is for incorrect purge flow. An emissions thing. Not sure it that would be a contributor to the problem.

 

Sorry I gave wrong code.
There are 2 now- P0442 & P0455 being small and large evap. emission system leaks.
Back in hills and confirm vents switching to defrost then back to dash vents at top of hill. I didnt know vents were controlled by vacuum but guess fixing them is my next step. If I could I would find the "blend doors" (I think they're called) and screw them permanent to dash vent position.
Sort of a side question this is happening when engine under load and "almost" kicking down the tranny. Should I have my overdrive turned off over these big hills? Asked another way when should you turn overdrive off?

 

Wouldn't matter. It's the loss of vacuum that is the problem. At higher RPM (like, if you downshift) there isn't much vacuum either.

Check valves, and make sure the vacuum reservoir doesn't leak will deal with most of it. In order to completely eliminate it, you'd need a vacuum pump.

 

Thanks so much
New territory for me. What valves? I'll find and check the "reservoir".
is a "vacuum pump" a replacement swap or an add on?
Sierra Nevadas in 2 days.
Indebted.

 

Vacuum pump would be an add-on.

Check valves are on the vacuum lines between the intake manifold, and the firewall. According to theory, there is supposed to be two of them. You can get replacements at napa pretty cheap. Somewhere in the second gen ram section there are even part numbers. (wild vents thread in FAQ section.)

 

Got it-
not to push my luck but while you're on "vacuum pump" a replacement item or some kind of addon the the van never came with

 

Van never came with one.