You need to check the vacuum lines for the a/c system for leaks, breaks and loose ones first.......
Your front blower motor has gone out. There is a front and a rear blower motor.
My ac blows only in the defroster and not any of the other vents i have 98 ford windstar 3.8 v6
The air of your Chevy trailblazer 2004 blow out of the front vents when the air conditioner is on because the air condition is faulty and it needs repair.
The blend door actuator may not be working.
Check your fuses.At first
Possible blockage in the rear air units expansion valve. I just replaced mine for the same reason.
probally closed or clogged
The AC does not blow on the main front vents. Only rear and defrost.
Under the hood in front of the transmission dip stick is a vacuum line. If it is disconnected or split it will make the air vents not work. If that's not it check your fuses.
It sounds like your vacuum controls are stuck on the defroster I had that happen and I sprayed a lubricant into the vacuum lines and it cleared up
You probably have a faulty rear temperature blend door actuator. Remove the left rear trim panel to access it. Be sure to review "Related Questions" below for much much more on Windstar heating/cooling problems
why dont bottom vent doors not open on 2001 gmcsonoma