My church's 92 B250 has this problem. When using the heat/ac/vent, when you accelerate the airflow goes directly to what seems like the defrost vents.

Is it the switch, or is there another issue which I'm not aware of.

Thanks in advance.

check for a vacuum leak.

Vacum leak or the vacuum check valve for the AC/Heater system is bad. When no vacuum the AC/Heater system is made to go to defrost as a safety precation. That way if you loose vacuum to the system and doors you will still have defrost to keep windows clear in winter. Ron

i agree with ron. when i was flipping minivans a while back, the 91-95's had the same problem. most all turned out to be in the switch, or the switch connector with all the vacuum hoses. i don't remember which though........

92... last of the square body's... got the 6 button control much like the 70s cars did... I have had that problem on a couple of Mopars over the years, CRS is preventing me from remembering what I had to do to fix it.

We are still using our 92 B 250 as well.

When towing and under extended acceleration it does the same thing.
I am calling annoying at this point, and most likely a bad check valve.

The problem exists up into the late nineties.

https://shallowbottom.wordpress.com/2008/07/08/dodge-ram-hvac-air-vent-blues/

Chrysler came out with a larger vacuum check valve later for the vehicles. I think the larger check valve that has a small resivoir built into it (its about 3 inches long and 2 inches wide) came out in the mid 90's and it can be used on any Chrysler vehicle that uses vacuum for the AC/Heater system. I did see a lot of the original smaller check valves go bad. Ron