OK I had a leaking AC evaporator and compressor(I found out after putting uv dye in the system) and after four years I decided to fix my AC. My system was already empty so I didn't need to have the system evacuated. There is a write-up on how to change the compressor so I'll focus on the evap, orifice tube, vacuuming the system, and charging.
The evaporator is directly under the maxifuse assembly. Disconnect the positive and negative batt cables. Remove the strut bar, maxifuse assembly, and any wiring in the way(there is one loom that bolts the the firewall that can be disconnected, the other one I left alone). I also disconnected both heater hoses. Next I removed the accumulator dryer and the bracket that bolts to the back of the block used to lift the engine. (pic#1)
Next I removed the blower motor and what looks like a temperature sensor from the top of evaporator housing. Now you can see the housing that the evap is inside of. There are about ten screws and bolts that hold the housing and plastic cover on.(pic 2)
Once you remove those screws and miscellaneous brackets the plastic cover can come off. WRONG there is no way of removing the cover unless you cut it. If you look closely GM has already placed a groove for you to cut through and even printed cut line on the cover directly below where the evap piping enters the housing.
With the plastic cover off you can now see the metal cover. There are about six small screws that hold it on. And a hidden screw on the bottom that threads into a plastic fitting that you have to squeeze in order for it to fit through the hole in the metal cover.(pic3)
The metal cover barely slips between the firewall and the engine. And now you see the evaporator, it isn’t held in place by anything. Take the time to clean out the box and make sure the drain is open. Put the new evap in and put everything back together.(pic4)
After everything is back together on the firewall I would suggest replacing the orifice tube. It is inside the high pressure line going from the condenser to the evap. About two inches from the connection between the line condenser you’ll see some indentations in the high pressure line. Disconnect the high pressure line from the condenser and stick some needle nose pliers into the line, and pull the orifice tube out. Replace it making sure you put it back in the correct way.(pic5)
I replaced the accumulator/dryer and replaced the o-rings at all of the connections in the AC system. Then I rented a vacuum pump and AC gauges from Autozone. I vacuumed the system down to -30 on the gauges for two hours, then disconnected the pump and watched for any leaks for six hours. I put 8 ounces of oil in the compressor so I then subtracted the oil from the total amount of refrigerant required for the system. I charged the system, and it’* been about 3 weeks and no leaks.