Hi,

I have a 96 dodge ram 1500 pickup, bought used. When I go up a hill or accelerate hard the interior vents temporarily switch to the default 'defrost' position. The shop installed vacuum check valve that lasted about a day then failed. I guess it's supposed to maintain the vacuum only in the vent controls when the manifold vacuum drops(engine under load).

The check valve was added, it does not origionally come that way?? Did new 96's have this problem or is there something else thats broken causing this problem? I'm guessing that if I had vacuum leak that the check valve would not have temporarily fixed the problem?? Any ideas why the valve would have failed, I found another post a couple of days ago where somebody had the exact same problem, the valve also quickly failed..

He solved by installing a vacuum container/resivour??

thanks, bill

 

I think you have a broken vac line in the engine compartment. There was a TSB on this (I think) and I remember several posts on this as well. I'll take a look for them.

 

here is some useful info... http://www.pavementsucks.com/forums/...froster+vacuum read the 2nd post down.

couldn't find the TSB yet...

 

Thanks, i would appreciate it!

But if I had a leak in the engine compart, why would it only show up while the engine
is under load(uphill/accel). I'm not an expert, but I guess as the throttle plate opens the engine can suck in air less restricted(thus less vacuum).

Maybe I have small leak and it's only noticable when the vacuum level drops??

I'm stuck trying to understand why it doesn't always fail(going to default setting;defrost)

Still the check valve worked for a day(maybe less) so it's definitely a vacuum problem..

 

to me it sounds like the check valve is no good or you have a leak inside the cab. if the the defroster flap goes then I'd say your not holding vacuum inside the cab (check valve or a leak inside the cab). But I'd still check out the other stuff under the hood.

 

The funny part is I found a similar post, the guy had the exact same problem, installed the check valve and it failed 'shortly' for him also. Is it likely both our's cv would fail, or is there something else going on?

 

may be the design of the check valve. i'd get the one from dodge.

 

It did come from Dodge...

Whats the easiest way to determine if I have a leak??

Can I disconnect the line at the engine and connect it to a vacuum and gauge?? Pump it down and see if it holds?? Or will it normally fall off??

Thanks for you help! bill

 

I would expect it to hold for a bit using the vacuum pump, if it falls of right away then there's a leak. Think about how it's supposed to work, as long as there is vacuum it will keep the air flowing in the direction you want (vent, floor etc)... no vacuum, flow to the defroster.

Can you post what your findings are... for the next guy who has this problem.