My mech. added dye to the system but could not find a leak that is what lead him to believe it is the evaporator. Do you know why the a/c wont blow any air out the vents? Thanks so much!

If he suspects the evaporatoris leaking. He can pull the side panels out from the trans tunnel and remove the drain tube from the heater box if evap. is leaking there will be a trail of dye runnin out of this hole.
Is the blower motor running?