Dodge Repair: Diverter Door, dodge ram 1500, vacuum lines

Question
I have a 1997 dodge Ram 1500 2 wheel drive with a 5.7 and automatic. My problem is with the A/C Diverter door, it changes from Dash discharge to defrost when a load is put on the engine,such as going up a hill. A vacummn problem for sure, but I cannot find a leak. Do you know of any common problems that cause this symptom?

Thanks

Bob

Answer
Hey Bob,

I'll trade you my 5.9L for your 5.7L because it's lacking some power.  Actually, I wish they did come with the new hemi 5.7L but I think you may be mistaken on displacement.  They only offered the wimpy 3.9L v6, the 5.2 and 5.9L v8's in the 1500 series gas engine categories.  

But regardless, you've got a problem and I think I might know the answer.  Your dash doors are controlled by a vacuum system.  When you accelerate engine vacuum goes away briefly inside the intake.  RPMs pick up, the vacuum starts to return and you continue to accelerate.  When this happens anything that is controlled by vacuum is subject to bleeding back and not holding their end components anymore.  

On the side of your intake manifold you will see several vacuum lines coming off.  One will have a diaphragm in it.  Some are all black, some are black and white and I think some are gray too.  Additionally, you will find one in the vacuum lines along the firewall probably just to the passenger side of the intake.  Take one out (note the direction it was installed in first) and try and suck through it.  Flip it around and do the same.  The check valve/diaphragm should block flow in one direction and allow it in another.  If you've not got that then you've got a bad valve.  Swap them out and you've more than likely fixed your problem.  Check the other the same way.

If you don't find a problem there then you may have damaged or pinched vacuum lines somewhere.  The most common place is near the battery.  
Let me know what you find.
Doug