Hate to see this so often and respond to an old thread but few understand how a GM AC of the 80s works.
First the DA6 compressor (early cars) was flawed from the start, Replacement is an HR (Harrison redesign) 6.
Are two levels of warnings:
- low refrigerant - can add more
- very low refrigerant - compressor is off - usually need to disconnect negative lead on battery to clear.
OK any time the compressor is opened for replacement, I flush and replace with R134A. By this time most have already been converted.
- to properly convert usually means replacement of compressor, dryer, oriface tube (white), O'rings, flush, and compatible oil. Missing any usually means going back in again. I then pull about a 50 micron vacuum and leave overnight to remove any moisture evaporates) and leave overnight to make sure are no leaks.
With a "very low" the system is usually empty and needs a full charge. Once negative side of battery is R&Red and before starting car add a can of refrigerant. This will bring the static pressure up to about 50 psi. Can then start engine in auto and add more to suit (usually about a can and 3/4 for R134A and an Allante or Reatta (same HVAC system) compressor should keep running.
- I generally use a 24" shop fan in front of the rad to keep high side pressures from going to the moon.
When done I like so see 35-45F at the outlet on high max cool.
Being a Floridian all of my cars have AC and all work.