First, go here:

http://www.epatest.com/

Pay the ~20 and get the 609 certification. Its open book and not that difficult.

Next, go here:

http://store.lenzdist.com/

and buy a couple 12 oz cans of R12 along with the proper gauges.

Do it right the first time, you'll be much happier.

__________________
Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE