Auto Air Conditioning & Heater Repair: heat & air blower, vacuum line, blower works

Question
my 1991 astro van blower works on defroster but nothing blows from air conditioner vents, is there a control that switches air back and forth?

Answer
In most cases the problem is a broken vacuum line from the engine that goes thru the firewall and in under the dash.

What mechanical work or ANY kind of work has been performed on the vehicle recently ?. As most problems that occur after a recent repair was made can be traced back to the area of where the repair was made as an electrical and or vacuum line may have been knocked loose. Look around in the area where work was performed