Hello & Welcome to JA,
Condensation can form when there is an air leak in the evaporator case.If the leak cannot be stopped ,replacement of the evaporator case is needed.
If the evaporator case that you're talking about is the tray that fits underneath the dashboard, under the glove compartment, (12 inches x 18 inches, by about an inch high, [my estimates]), that tray has been replaced and is new. As I said, the Buick dealer has sealed this case a number of times, and there are channels within the case specifically for sealant. These channels hold a soft but semi-rigid sealer that fits in these channels and compresses in both surfaces as the tray is put into place. The drain is through the firewall, roughly in line with the glove compartment, and condensation leaves huge puddles of water on the ground as it drips to the ground through this hole. This drain appears fully functional.
You say "Condensation can form when there is an air leak in the evaporator case." There is no question that condensation is forming. That happens by virtue of an operating air conditioner, and the function of this tray, I am told, is to handle this condensation which is normal when the AC is operating. I have also been told by the dealer that it acts as if the air flow is being restricted in some way, but they assure me that such is not the case.
I was hoping that there was some unknown, little detail that the mechanics and body shop personnel are overlooking. Some small trick or something that is being overlooked that is peculiar to a 1992 Buick Roadmaster AC system.
The Buick dealer is Rahal Buick in Marianna, FL, and they have been in business there over 60 years. They are quite familiar with Buicks. They are excellent people and I don't know where you could find any better, but this one has them stumped.
I am sure your Dealer has been in business long enough to know the product,but what you do not realize is the people in the shop now are not the seasoned GM technicians of years past ,they are a bunch of parts throwing kids who have to ask someone Techline when a problem comes up.
I have repaired vehicles for over 40 years ,a condensation leak is not a one time thing.I have repaired vehicle with ac leaks in all lines of GM.The drain is functional or you would have a floor board full of water ,like a flood.If you think you have a one of a kind problem you are sadly mistaken.The small tray under the dash is NOT the evaporator case ,it is only a small part of the evaporator.
If this problem has them stumped,they have to be some of the dumbest people ever to manage A shop.I would be ashamed to give a problem like this back to a customer & admit that I could not fix it.
In reading your post I can only laugh at the scam they have pulled over on you.This is not a shop it is a circus.You need to find a "real GM technician" , a seasoned person that is qualified in repairing all parts of your GM vehicle.
Sorry John, but your answer is not acceptible. Throwing rocks at my dealer as you have in your answer above and telling me to find a "real GM technician" is not a solution to my problem that I would pay for.
Thank you for your time, anyway.