What amount of superheat is recommended for R-22?

Superheat depends on the type of metering device you are using in the equipment as well as the current state of the load. With a fixed orifice, the superheat will be high, about 20 to 30 degrees when the box is warm, down around 10-15 when the box is cold. With a txv, the superheat should be constant, normally between 10-15 degrees.

It is best to check the superheat at the outlet of the evaporator. this will ensure that the compressor does not slug with liquid refrigerant.