A/C problems?

For one thing dexcoolant is for 2000 and above, and he is right on the threads comming out of block, if its not leaking and fans run properly you have a headgasket prob.

I just posted a reply to your first question before you included these details. The system will not work on only two ounces of refrigerant. For all practical purposes, it's empty. Most systems on larger cars take around 1.5 to 3.5 pounds of refrigerant. The low-pressure cutout switch would trip before half of that was lost.

I would get a second opinion, preferably from an AC specialty shop or a radiator repair shop. Most of them do AC work too. If they too find the leak is in the evaporator, that is fairly common but there is no way anyone could cause it to leak intentionally or unintentionally. It is buried way too deeply inside the heater box. Chalk that up to a bad coincidence. Also, refrigerant escaping from there could take hours to leak out completely, and as it does it expands which is what makes it get real cold. That alone can make it look like the system is working. I recharged the system on my minivan years ago and was impressed when I saw frost coming out of the vents. It was really cold, but the next day it was empty. It was the escaping refrigerant that was making the "cold", not the system itself, and as I realized later, that frost was the refrigerant I was seeing. You can't SEE cold.

Sometimes inexperienced mechanics use the wrong terminology when they say "evaporator". If they are pointing to the unit in front of the radiator, that's the "condenser", and it is another common failure item. That one is relatively easy to replace. Since they said the engine needed to be lowered, (something I've heard about on some GM cars but have never done), that does point to the evaporator in the dash. On most cars the steering column is lowered and the dash assembly is pulled back to get the heater box out. It's still an expensive job on any car.

If the diagnosis IS for the condenser, have the mechanic point out exactly where the leak is. Typically it will be in a corner where the aluminum corroded. If it's in the middle in the front, it may have been hit by a rock. If it looks like it was hit in the back, I'd suspect the first mechanic hit it with a tool. The tubes on the condenser are pretty tough and accidentally bumping it would not damage it. They're also fairly well protected. The person giving you the second opinion will be better able to evaluate that kind of damage.

Do you mean it is coming from the defroster vent?

Under the dash in the HVAC system are vent doors. They are what direct the air flow. I believe in 99, these vent doors were actuated by engine vacuum. Based on that, I feel there is a vacuum leak not allowing the vent doors to work. Check around for broken, disconnected, or damaged vacuum hoses. Also, there will be a supply hose that runs from the top of the engine through the firewall into the vehicle. Make sure it isn't disconnected or damaged.

If you found the end hose, one way to get a general area it is, where was it sitting when you saw it? The area is usually around there close. The piece that broke off may still be on the end and you should be able to find it after some looking.

Its low on freon, you have a leak

Suggest take to a shop that specializes in AC work have diagnosis should be minimal charge the post results will advise.
Ask for High and Low side pressure readings