Question, do you have frost all the way up the suction tube back to the compressor? I was thinking that 16oz of R-12 is a bit much for that size of a machine, the system is basically the size of a vendo V90 & that only takes 12-oz. of freon...did your machine have a specification tag that told you how much freon to charge the system to? just curious...
Insofar as your T-stat issue, if it were bad I couldn't see how it would regulate the temp between 40-32/deg. Fahrenheit, it would be the same (too cold temperature all the time regardless of the dial setting), but if the thermostat was be doing it's job, then the temp would vary with the dial setting, does the condenser fan shut off when you turn the thermostat off? (or just the compressor? )