I just got a 96 blazer this summer low miles and rust free. The only issue I have noticed so far is with the heat. The volume of air coming from the vents in any of the positions is very little when the heat is on full hot. When moved to cold the air volume greatly increases, double or more than when it is on full hot. Any ideas?

 

Can be a couple of things.
Obstruction from debris, leafs a mice's nest or simply a control disconnected and the door does not open for the warm air.