Toyota Repair: ac on 2001Toyota Sienna, compressor clutch, sight glass

Question
When a/c is turned on the compressor clutch does not seem to be engaging. Looking into the sight glass, can't tell if the system has freon in it. Is there a special adapter for charging the system.
 Any ideas would be helpful.

Answer
Most of the time the compressor does not turn on because the freon is low, there are self service recharge kits available at most autoparts stores as well as wal mart , target etc. just follow the instructions that come with it, there is everything you need in the kit.