Yama is right about the dryer and exp valve. With A/C there are a few areas for leakage and most of them are hoses, sometimes the ports leak and now and then it is the compressor shaft seal. Almost 100% of the time we have a new suction hose made with a 134 port added so we can get at it. (runs from exp valve over the engine and down to compressor) This is also a common hose to leak as it gets super heated by the exhaust manifold. The high pressure hose running from the compressor to the condenser is also a common failure hose as some one in the past usually hasn't anchored it correctly and it vibrates loose or cracks. The next common hose is also a high pressure hose it runs from the dryer to the exp valve. it is also next to the exhaust manifold and is usually dry and brittle. You can have a high pressure port installed at this point but we usually don't.. I have a local rad shop make these hoses for me as they are cheaper than Volvo and I can get a good quality hose that is a barrier hose to handle R134. Volvo never had ports in these hoses. You need to drain and flush the old R12 oil from the system and especially the compressor and add at least 6oz of Ester oil. PAG is for cars that came with 134. The dryer has only a 3 min life expectancy in humid air when the caps come off. SOOOOOOOOO when the dryer is installed the vacuum pump needs to start lowering the atmospheric pressure in the system immediately, not in 5 min's. The amount of R134 charged is critical to a good system so you will need a digital charging station to do this not the cans of 134 at the auto parts store. If you try the cans make sure they do not have sealer in the 134. this screws up charging stations. We see a lot of 240 a/c problems usually caused by a lack of knowledge by the person doing the work. A/C is not really a DIY, project. My advice is to find an independent Volvo repair shop and have it done by people that know what a 240 is and they have done this job many times. A/C shops may be good but in my area there about 25 shops and only 1 that I know of could do a proper job on a 240. A final note the 134 system is ok when you install a cooling fan in front of the condenser.( the larger diameter the better) Use a relay and have it come on when the compressor comes on. a final note remember to always put refrigerent oil on all connections and replace all black "O" rings with 134 compatable colored "O" rings. You said detailed is better for you. Hope this helps. By the way my daily driver is a 1990 244 that I turboed and the 134 system is just fine in central Florida.