Toyota Repair: 1992 Camry A/C diagnosis/estimate question, r 134 freon, r 12 freon

Question
Hi Ted,

Have a 1992 Camry and the A/C has stopped working.  The vents blow air, it's just not cold.  I just got the car, so I don't know much of it's past repair work.

1.  Are there any tests I can do to help pinpoint the problem before I take it in to the mechanic?  I don't know if the freon needs to be filled, or if there's a leak, or if the whole thing needs to be overhauled.

2. Can you give me a rough estimate for a freon fill-up?
3. How about an estimate for an overhaul?

I'd be happy to perform any tests you can suggest and post my results here so others can benefit.  I'd like to have a better idea of what I'm facing before I take it in and am at the mercy of the mechanics! :)

Many thanks in advance,

Brian

Answer
There is a good chance that it is low on freon and there may be a leak, the system should be connected to pressure guages first to determine if this is the case then the remaining freon,if any, is evacuated. 1992 models used R-12 freon which is no longer available in most locations, I would recommend having the system retrofitted to the R-134 freon which is much cheaper. After that the system is filled with the specified amount of freon and checked for leaks. A/C systems are usually not overhauled, just serviced and any necessary parts replaced. Unless there is another problem, retrofitting and the service should run about $300-350 parts and labor.