by Michael Lewis
Servicing automotive air conditioning, particularly with R-12 freon IMHO, is better left to the pros who do it every day.
There are several weak points in most systems, most notably, the compressor seal, which is often a carbon seal relying on a thin film of oil for complete sealing. That's why older GM compressors are particularly bad. Many do not get run in the winter, the oil dries out and the freon escapes. Those long runs of hoses are subject to the same deterioration problems as our VW gas lines, however there is considerable pressure on the pump side. The system, including lines, evaporator and condenser must be completely leak free.
To properly charge an A/C system, it must be thoroughly evacuated, cleaned and a considerable vacuum applied with a vacuum pump. The reciever-dryer should be replaced at service time, as even opening the system can allow moisture inside which will shut the system down, first hot day.
Last, handling of pressurized freon is dangerous, particularly if it
escapes and hits the eyes. Corneal detachment can occur if this happens.
If you do decide to do this, wear proper mask type eye protection which
completely surrounds the eyes, good leather gloves and make sure you get
quality gauges. You _can_ pull a head of vacuum with the compressor, but
nothing like what they can pull in a shop with pro gear. That vacuum is
darn near the most important part.