I have a kelvenator 2

Evaporator temperature is what controls on and off operation and indirectly controls the case temperature. The charge in these system does have to be correct to the ounce. To much charge and the evaporator Pressure will run end giving a higher temperature. To little charge and it will only frost part of the evaporator. These system are critically charged systems.

These type of systems are controlled by the thermostat which should cycle off at a preset temperature and not return to the on position until the cooling coil reaches 37-38 degrees. Setting the control to cold will cause the evaporator to freeze up. Turning the temperature control to the off position will allow the fans to melt the ice from the coil. When reseting the control set it to #1 or 2 setting to begin with.

Also an old unit with an old compressor may not allow the unit to reach design temperature before freezing up the coil.