a/c and heat won't blow if truck is accelerating?

hey guys,
 
My a/c doesn't work hasn't worked at all all summer (the system is charged and the condensor gets frosty if it is on, but won't blow into the interior).  When the a/c is on, I feel warm air coming in at my feet (slightly warmer than the outside air temp.)  But, I tested my heat last night since it was cool here, and it only wants to blow when the truck is in idle, or driving but under limited load...if accelerating, it barely blows.  What causes this?  I was told there is some sort of control unit behind the glove box with a nylon gear in it that wears out...?  Anybody know what it is or how to change it?
 
Thanks,
Nick

Sounds like your HVAC system isn't directing the airflow properly.  It has to switch the mode door to direct airflow through the A/C core.  If it doesn't do this, you won't get any air...  You may have either a vacuum leak in the engine compartment or a faulty control unit.

After reading your original post again, I'm not sure if you are saying that only the COLD air will not blow in, or that neither cold nor hot air will blow in...
 
If you crank the blower motor on high, what does it do at idle vs. what does it do when accelerating?  Does the volume of air change, or just the temperature?
 
 

If I am accelerating, the volume of air coming in is drastically reduced, basically to nothing.  Last winter, the Heat didn't work for about one week (which happened to be the coldest week)  The A/C never really blows in, and warm air is onstantly coming in from under the dash.

Wow, that's odd... the only thing I can think of at the moment is, I wonder if the bearings in the blower motor are going bad and the motor binds when you accelerate.  I know it sounds odd, but that actually happened with an 87 cavalier I had, bearings were worn out enough that every time I'd hit the throttle the blower motor would slow.  It never stopped blowing though...