A/C condensate leak

Can't stop. Anyone have idea, the a/c unit is leaking condensate from somewhere high along the inside firewall. Has been in shop for 3 weeks and thay don't know where to go other than removing entire dash and full a/c unit tp look for problem. This is a '94 Skylark 4-cylinder. No one seems to have any ideas, how about you guys!! Thanks

When the car is running does the condensation from the ac drip onto the ground under the car? If not then the drain could be plugged.

The factory-applied insulation-seal molding applied to thefirewall prior to installation of interior components dried out and caused the a/c handler to become loose from the firewall; vibration inceased the side of the bolt holes in the plastic case. The unit became loose, and the bottom pan, including the drain to the outside quit sealing to the upper case. When the a/c operated, some of the condensate went outside, but most of it went inside the vehicle. Dealer re-mounted unit and resealed it. BTW, they said they couldn't get a replacement liner, panel, whatever, to go on the firewall.