my husbands 98 ram 5.9L is having issues. when he accelerates while driving down the highway, or at any time, the dang a/c stops blowing. he sets controls like hes always done.

when he stops at a light or stops period, no acceleration, the a/c blows great likle it's supposed to, nice and cold. temperature is not the issue. it's the blowing/blower, as opposed to NO blowing.

we live in texas and its NOT cold here.

what the heck can cause this?

the poor guy is melting cause he's made of sugar of course (and he comes home in a really bad mood).

hellppp!

 

Quick fix found!!!





Let him drive your car.
Seriously though, It sounds like a vacuum leak. hopefully others will chime in.
You might want to try searching " wild vents"

 

He's experiencing a loss of engine vacuum. have him look over this thread:

https://dodgeforum.com/forum/2nd-gen...ild-vents.html

Somewhere in the vac system is a leak, cracked tubing, plenum gasket shot to heck, etc.

Idling is the time when the engine has maximum vacuum, so it's fine at that time. Once he starts moving, the engine vac drops and he experiences this issue.

There are lots of systems that require engine vacuum to operate, and they could all be affected, though he might not have used them as much.

the HVAC, Cruise Control, CAD engagement of the 4x4 system, brake booster system (that makes it easier to apply the brakes, they won't fail completely with no vac, but will be harder to push), evap system and overall engine performance rely on vac to work correctly.

 

thanks we replaced the plenum about 3 yrs ago and still having nightmares about it. we just don't know where to start. truck is work truck and on the road 24/7. does he need to stop using a/c so vac sys won't be compromised? he says hes sure not the hoses under batt tray check valves hes not that familiar with. but he has always come thru and mostly fixed things himself. just finding the energy and time to do so. oh and the money. sigh, money. oh and he says so far brakes are not hard to push down. any more advice? i read thru the posts/link you kindly provided and "got" some of it but he'll have to read to know more. well try to find the time to actually sit down when dead tired and try to absorb it. thanks again

 

Well, to ease your mind a bit my truck has always done it with no driveability issues. I just thought it was one of Chrysler's genius ideas.. guess not. Gotta love this Texas heat though..

 

The brakes will more than likely never fail, as the booster canister holds its own vac reservoir for a good three assisted brakings.

There is a "tree" of vac lines on the passenger side of the engine that connect to the intake manifold, the widest point in this tree is the check Valve. You can remove it and test it by lightly blowing thru each end. Air should go one way but not the other. There is another check valve along further up one of the lines that branches off of the tree. To reinstall, The flow should always go toward the intake manifold so vacuum can be pulled on those lines.

 

Continued...

If a check valve is bad replace it. Unfortunately I've had no luck with finding the correct size check Valves at the parts stores, seems to be dealer only.

Trace all the hoses that go into the throttle body or intake manifold. If they are cracked, replace them. If they are the hard plastic ones, they can be fixed with a bit of rubber tubing that can fit over the outside of the line. Just cut it at the crack and stuff the plastic lines in the rubber tubing.

Also, how exactly did you fix the plenum? Did you reuse the same belly pan that was stock, or did you buy an aftermarket one made of aluminum? They can blow a second time if you reuse the stock pan. Might want to check for oil in there just to rule it out. It usually takes a pretty large vac leak to cause the vents to go nuts. Might want to double check the torque on a few of the intake manifold bolts as well.

 

There's a white line (OEM) that is hard plastic like material that runs behind the intake manifold and routes down the driver side of the engine down under the firewall and up and over to the tranny.

Check that line. HOW: remove both ends and plug the end down below. Using a hand-held vacuum pump, apply vacuum to the upper end of the line. This is the one that is going to be connected on the PASSENGER side of the intake to a T-fitting. Disconnect that line and apply vacuum.

If the vacuum falls, you've got a leak / hole in that line. R & R. (remove and replace)

Now, there's also a vacuum switch at the top of the tranny where, quite a few lines (4) come into a rubber boot. What I don't recall is the schematic for that vacuum circuit. There is a switch that also, may be leaking thus causing a drop in vacuum at the engine as well.

What I do if I just want to find it quickly and I don't have time to test every point, I simply run a smoke test. It's a pressurized test that pumps smoke into the lines and, where the smoke comes out, there's your leak.

If you can't afford the tester kit, any shop can do this and, the guy that used to do mine used to charge me 22.00. It was that cheap to do in So Cal where, shop labor is 95 / hr.

I would go that route if I were you to find it quick, fast and cheap.

CM

 

ok guys he located the vac leak real quick...very lucky...i have attached a photo of the line...what is it, where do we get one those kind of questions. hope you can tell by the pic. all and any info about it and any installation help if tricky, would really be appreciated. thanks.

 

Easy, find rubber vac hose at the parts store that is slightly smaller Inside diameter than that plastic tube is on the outside. Slide about 1 inch of rubber hose on one end and 1 inch on the other end. Should cost about 50cents unless they make you buy a foot of hose.