Humidifier not working.

My Kenmore model 580.53650200 runs but only shows frosting up on the first finned tube and a little on the second tube. The frosting area is very cold but as far as I can tell, the rest of the finned tubing is not getting cold. I believe this means that the refrigerant gas is low as in a leak somewhere. Can I fix this myself? What equipment would be required? The label says it uses 9.9 ounces of R22.