Originally Posted by parallelcircuits
I would start by putting some AC oil in it, 2.5 ounces would probably be enough. I know everybody says you are suppost to have a licence to mess with the AC but any autoparts store carries the hose, pressure gauge, and oil you will need to do this, Wal-Mart even carries what you will need.
I think you're mixing two different rules here. You _do_ need licensing of some sort to work on the older R-12 (Freon) systems, which were used in Bonnevilles up to and including the 1993 models. Newer ones used R134a refrigerant instead of R12, you don't need a license for that, and it'* the R134a kits that are available at Wal-Mart.
If you've got an R134a car and it just needs a little refreshing, like our '96 Trans Sport that was working but just not very cold anymore, there'* a nice Interdynamics kit at Wal-Mart that comes with a refill hose _and_pressure_gauge_ and three 15-oz. cans of R134a with oil for something like $25-$30 or so.
With the gauge I was able to measure the current system low-side pressure in the Trans Sport, and add just enough new refrigerant to bring it up to where it was supposed to be. (Basically you stay the hell away from messing around with the high-pressure side; the scale of the refrigerant gauge goes up to something like 200 psi just so it doesn't blow apart if some numbskull hooks it up to the wrong hose, but its operating pressure is actually down around 30 psi or so on the low-side hose.) I know I did it properly because now my wife keeps closing the A/C vents on her side of the minivan again, like she used to when it was new. I like my A/C _cold_.
If you don't want to do it yourself it shouldn't cost much to have some oil put in it but I have never had mine serviced, always did it myself, so I don't know how much.
It depends on what components were replaced, if any. According to my '93 service manual (which was for an R12 system, so don't assume this will be correct for R134a as well), if you replace the evaporator you have to add 3 ounces of oil, a new condensor needs 1 ounce of oil and a new accumulator needs 4 ounces of oil. The oil is added in the low-side input port of the accumulator. The local Goodyear place wants $1.00/ounce for the 525-spec oil in my R12 system, so I assume the R134a-compatible oil would be less. It'* basically chump change.
Whatever you do, check the manual first. It'* easy to screw up the system by adding the wrong amounts or wrong types of refrigerant or oil.