Reciever dryer should be changed in two condtions, if the a/c system has been open for a while, and two if it's been over five years and you are opening up the a/c system for something, good idea to replace it then also. You are correct a desseciat bag is inside the reciever dryer and quickly absorbs moisture from the air, so work quickly to get it on the fittings and get the system evacuated as soon as possible (not days, hours at most).

The amount of R-134a (generic name called Suva) is usually no more than 80% the amount of R-12 (commonly known as the generic name Freon). A retrofit is NOT just taking out old oil (which is usually mineral oil for R-12, although I believe the old system used also POE...have to look at specs) and refrigerant and putting in new oil (usually POE for Honda's and Toyota's...or NippoDenso oil #8 as it is known). There is usually the requirement for a high pressure cutoff switch to be installed, to replace the high pressure valve (I think that's the name, I forget right now). Sometimes you may also need to install certain barrier hoses and a pusher fan, depending on the vehicle.

This is what I tell people, if your system was designed for one type of refrigerant, stick with it! Retrofitting, will decrease efficiency of the heat load removal from the interior of the car.

By law, a vehicle with an a/c system must have a decal underneath the hood somewhere, where a/c capacity and oil type is indicated for that vehicle. The Honda's have a silverary color decal and is usually just beside the top radiator support. That should tell you the type of refrigerant used, the capacity, and oil type. Per the Montreal Protocol of 1990, by the end of 1995, all production of R-12 was to be ceased, due to the chlorofloro compounds that cause ozone depletion. Honda's 5th gen accords and up, contain the new EPA approved refrigerant which is R-134a. There are blends out there and for those, they have special fittings so that you don't contaminate refrigerants.

If you live near Sacramento, CA and can wait for like three months, I can install a new reciever-dryer and vaccum your system and charge it up. You'd be responsible for parts and refrigerant cost, I think R-12 is $3.00 an oz...and that's damn cheap! Oh and for the love of God, please do not buy the store bought cans with sealer in them. They may work for a while, but it only makes it more difficult on the techncian to service your vehicle in the future should a problem arise in the a/c system.