while under above normal load(accelerating entering on-ramps, driving up hill), air coming from the vents will transfer to the defroster vents and leg vents. if i let off the gas, or maintain speed, it will go back to blowing air from the cabin vents.

ive tried cycling the dial to "max AC", "vent", and "recirculate", but it makes no difference. it will still switch on me while driving. ive watched the little plunger behind the glovebox move, while changing the settings. it seems to be doing what it needs to do. im thinking the problem is vacuum related, but there is no presence of a leak. ive also pulled out the HVAC panel, and check the vacuum line connections. all felt good and tight.

problem seemed to have occured after i put the ASP plate kit on my manifold. what do i look for now?

its a 99 ram 318/5 speed 2WD, BTW.

 

I also have the same problem but have yet to care to go looking for the problem so if some can tell us both how to fix this. Some like hansonHVAC for instance

 

Vacumm leak

The truck uses vacuum to switch between the modes. It's also the purpose of the resevoir...to keep your settings from changing while you're under load/braking/etc. But if you have a leak in the system, the resevoir is useless [8D]

If the problem started after you messed around with your manifold, that's the first place I'd start looking for a leak.

 

the burning rom is correct. I had the same problem on my truck and it was a vacuum line that ran by the battery.

 

I had the same problem and this fixed mine... however I do not think you vehicle falls within range of the TSB...

http://dodgeram.info/tsb/1996/24-01-96a.htm

 

i didnt see a vacuum line near the battery. i saw a line coming off a "tee", that goes to a black plastic box inside the cowl panel.

that check valve is already there.

 

That "T" line that goes to a box under the cowl is your cruise control.

 

bump! lol

still having the problem. how do i isolate the vacuum leak?

 

If you cant find the leek i think theres a machine that pumps smoke throught the intake into all the vacuum lines. The smoke would leak out of any cracks. Not sure where youd get this done though.

 

replace your vacuum check valve(s)