My Ram, '91 model, flips between the defog and the dash vents when you start
up a hill. It don't have to be much of an incline either, just 2 or 3
percent, just enough to put a little load on the engine. I've had it to the
part changers over at the dealership and after $300 it is still doing the
same thing. Now they want to put a $400 part on it, a gas canister. With it
only doing it on an uphill slope it seems to me it would be a vacuum thing.
Anyone have any ideas?
It sounds like a simple vacuum check valve has gone bad. As I get older
and the memory deteriorates, posts like this help me remember why I don't
want to buy a new truck again or have anything to do with dealers.
Yep... check for vacuum leaks - common areas are the cruise control
diaphragm that sits under the battery tray (acid drips on the vaccum lines
and eats them away), the vacuum line going to your your transfer case, and
the lines from the case to the front axle disconnect (if 4x4). As BIR
suggested, it could also be the check valve on the line that runs to your
HVAC controls. Find the vacuum line off the back of your intake manifold,
and look for the check valve. Note which side connects to the engine, and
which goes towards the passenger compartment. Remove the valve, and try
pulling a vacuum (use a hand vacuum pump, or, in a pinch, suck it like a
straw) from the engine side. Air should flow freely. Do the same on the
other side. There should be restriction (no air should flow). If it does,
the check valve is bad.
I had a '94 doing the same thing. They come from the factory that way.
There is a fix that increases the size of the little vacuum canister
next to the throttle body. The factory one is about the size of your
little finger, the fix is about the size of a 35mm file canister.
Someone posted the part number and connectors for the fix on line but I
erased my copy when I installed it. Parts cost about $10 and 10 minutes
to put it on. No more problems. When you hit the throttle the little
cannister doesn't provide the vacuum buffer and the vents change from
dash to windshield.
and look under 24-Heat/AC for TSB 24-01-96A. This is the Dodge response
to the problem but this is not the fix that was posted on line. I can't
find a copy. The fix I applied was to replace the existing canister with
a larger canister from Dodge. If I remember correctly it is the same
canister that was installed on the Jeep Cherokee. The other parts were
miscellaneous rubber connectors from Advance Auto Parts. You might talk
to the Dodge parts man.
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