Heater vent change

93 transtport, push off button for heater/blower vents, then select vent, blower on high will start but vent will not change. lots of blower noise air comes out of bottom vents, select vent, def. or bi-lever will not change for quite a while after some time will change to the vent selection. What would be the problem for??

The vents are controlled by a vacuum switch either on the back of the vent control or somewhere under the dash. You could have a blocked line or a bad selector causing this problem. Check for both. You can probably find a used one at a wrecking yard to replace yours with.