Hello all,
I'm writing in w/ a quest about A/C my son just turned 16 and we found him a good looking 99 ram , 318 engine , excellent interior , but has something going on w/ the a/c . It cools very well , but on acceleration the air stops blowing f/ the vents in the dash and seems to route through the defrost vents near the windshield?? I haven't looked into it too far , was wondering if anyone here had any insight as to this problem??? Thanks in Advance.

 

Fortunately the answer is simple.
The check valve under the hood is probably leaking. Upon acceleration, the lower vacuum allows the faulty check valve to bleed off sending the HVAC system into failsafe mode which opens the defrost door. This valve is located on the right side of the intake manifold (one of several). The vac. line then goes up through the firewall and under the cowl to the vacuum storage box. That box being plastic could have also developed a crack/leak as could the vac. tubing, however, most times, it's simply the check valve gone south.
WC

 

Thanks alot, !! That's exactly what it was, went to the dodge dealer and picked up a new check valve , actually a larger one and it works perfectly now. . Glad I found the forum.

 

Glad to help. Ya gotta love the easy fixes! And thanks for reporting back. More people should.
WC

 

I have the same problem. My air goes out when in the throttle. My cruise doesn't work either. I know it's a vaccum problem, I just haven't messed with it. Did you cruise go out to?

 

No, the cruise seemed to be working properly. The vacuum line to mine looked like it split off to the wiper motor, didn't see it going to the cruise control, but wasn't looking for it either.