AC/Heater Blower during acceleration

I have a question about the AC/Heater Blower operation on
a 96 Dodge Ram.

During acceleration while running either the AC or heat when I accelerate
the AC or Heat exhaust is diverted from the dash to the defrost vents.

Now, I never noticed this occuring before but started happening after
Dodge replaced the MAP sensor on my truck.

My question is can the replacement of the MAP sensor cause this or during
the replacement they buggered up some vacuum lines?

Also, I know there is a TSB, 24-01-96, which talks about the same problem
I'm having but it just seems like too much of a coincidence that it occured
after the MAP sensor was replaced.

I plan on going down to the dealership tomorrow and speak to them, so any
assistance would be appreciated.

Thanks, Mark

 

I've had lots of cars that do something like this under full throttle.
Typically, a spring holds the HVAC dampers in one position and vacuum in
other positions. At full throttle, the vacuum drops dramatically often
letting the spring win the tug of war. I'm guessing that in your truck
the spring holds the damper in the defrost position and vacuum pulls it
to allow air through the other outlets.

I can't imagine replacement of the MAP sensor affecting this, but I
don't know the vacuum schematic for a Ram so I can't comment. I just
know that this general behavior isn't unusual. Also, many vehicles will
kick off the AC compressor when under heavy throttle. It isn't unusual
to lose AC temporarily when climbing a long hill.


Matt

 

Based on my experience on a Reliant with a similar problem, I would say
there's a vacuum leak which is putting the steady-state vacuum at a
level just barely enough to operate the defrost/vent controls normally,
then, when you accelerate the vacuum drops below that marginal
threshold.

Yeah - I'd look for a small vacuum leak.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

My Jeep Comanche did this often. We have grades here in PA that run for
multiple miles. The reservoir wouldn't hold out. The dealer installed
a second reservoir under warranty. That pretty much fixed it, but there
was still one grade, about 5 miles long, that I had to run at full
throttle with the old 2.5L 4 banger. After about 3 miles, I'd see the
HVAC system making uncommanded changes in setting...

Matt