ac "odd" behavior?

... but I've been surprised what "normal" is before.
I have a '97 Ram Van B2500, standard AC (front only). Under idle or cruising conditions, all is fine & ac comes through the dashboard fairly
strong (might need recharge).
Under acceleration or hillclimbing load, the ac comes through the lower (heater?) vents. When I back off on the throttle, the ac again comes through the dashboard. When the ac's coming through the lower vents, nothing comes out the dashboard.
So, is this normal behavior? If not, what would cause it? I know that the heater/ac are a single black-box unit, but my Haynes manual doesn't describe it very well.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Vent position (floor, panel, defroster) depends on a set of vacuum actuated doors. Under hard acceleration, vaccum changes, and thus so does the direction the A/C blows.
This is normal.
--
Max

"There are four boxes to be used in defense of liberty:
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks. It'll probably be less annoying after I recharge the ac.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
writes:

True, this is how the vents work, but my bet is if you've had this vehicle for a while that this is possibly "not" normal behavior to you else you wouldn't be asking about it now after so many years of ownership.
It hasn't always done this, right?
My own guess is you've developed a vacuum leak, possibly due to a broken vacuum line somewhere. Just "where" would be anyone's guess, but one of the more common places is right at the top of your cruise control vacuum cannister. If your vehicle has 'cruise' does it still work? If not, then you've found your leak. Fix the leak (replace the line) and you will have fixed your cruise and your AC. ;-)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.