airconditioning on 2001 Chevrolet Silverado 3500

How can I add refrigerant to the air conditioner in the truck..

If your air conditioning does not work well you may have a leak that needs to be repaired but check this link.
1 more answer
Go to a parts store & get a AC kit & start with one can of freon.You gotta find the suction line that has a connector which is off the AC pump.If it emty be sure to add a can of lubrican for AC & if its leaking put a can of sealer in before the AC Freon.Not sure how much it'll hold,around 3 cans.Also if its running when you put it in it'll go faster far as sucking it in.Just be carefull around the running engine,It'll get ya if your careless.