I am far from an expert but here is what I have learned: To diagnose internal a/c problems. requires that it be charged. Since it uses R12 that is no longer made, that is very expensive. Have you checked simple things like the fuse and wiring to the compressor, ground, and the switch on the console? Assuming those seem functional, I believe your next option is 1]do without; 2]bite the bullet and have it recharged w/R12 3]do the conversion to Freeze 12, an environmentally safe and cheap alternative to R12 or to R134a. I have not done this to mine but I know Groton and IPD sell conversion kits. BUT, after you convert, you then must trouble shoot. It could be anything for example a bad compressor, bad clutch on the compressor, bad seals allowing the refrigerant to leak, bad pressure switch. What shops do is add a dye that can be seen under UV light to detect leaks. The other part they replace is the receiver dryer which is like a filter because when a/c has not been used or when work is performed, minute particles like rust that has formed can block the small orifices in things like the expansion valve. I understand from this forum that the actual conversion is not hard and is a DIY job but then you must take it to a shop to have the system evacuated and refilled w/refrigerant. You might want to google "freeze 12" and see what it is about. I believe but can't swear it uses the same oil as R12 but verify this. R134a systems use ester oil, don't recall what the R12 oil is called but it is NOT compatible w/R134a. I also read a resonse to a similar q as yours this week on this forum to an a/c question that said he had added insulation to his roof, I assume under the headliner, which improves the effectiveness of Volvo a/c