Just bought a used 1998 Ram 1500 and the A/C quits blowing anytime I use passing gear or go past half throttle from a stop? I'm been told it is a vacuum line off someplace under the dash. Anyone know which one and where to look for that line? TIA.

 

welcome to DF. common problem. do a search on check valve for lots of posts, some with pics. there are 2 little check valves in the vac lines. they're small about the size of a quarter, maybe 1/4" thick. one just off manifold and one closer to the firewall. if not those valves then it could be a broken line anywhere between manifold and dash controls or even over on the cruise line.

 

+1 on the vacuum, very common prob for our trucks.

The easiest thing is to replace the 2 small check valves on the passenger side of the engine. Just trace the vacuum lines from the manifold, should see 1 very close to the inlet, splitting into a "Y" there. Then also there is another one hanging from some very small vacuum lines on the firewall, splits into a "T" in most cases, but should be easy to find.

Cost me $7 for 2 new check valves at Autozone, fixed it. Good luck!

 

Thanks for the replays! I took a week of vacation but am back now and will check out the check valves you both mentioned.

 

is it a 4X4? if so my vacume lines from my tcase to my front axle rotted out.. thats where my leak was

 

No, it is a 2WD. Still checking.

 

I have this issue too and was wondering if you found/fixed it?