Cornelius Compact 50

[fkg41]

My Cornelius Compact 50 is operating properly but delivers 40 degrees. Cuts off and on correctly. As I have previously mentioned in the Discussion Area, the chest type beverage box will not go below 40 degrees. Turn it any higher than #1 on the thermostat setting and it frosts up and hampers air flow and eventually freezes up.
Another thing I need to mention is if I put hot(room temperature) drinks in the box it will run for a day or two before cutting off even though in a few hours hours the drinks are 40 degrees. They are not stacked high enough to hamper air flow.        Is there another idea of what may be wrong from anyone out there?
This unit operates using R-12. The low side psi is 16 lbs. According to the Pressure-Temperature chart,16 psi corresponds to about 12.5 internal low side freon temperature. Since the unit should operate on low side at twice the saturated temperature the temperature should be 25 degrees going into the coil inside the box. Those are the readings I get.
I may not have done the right thing here but this is what I understand from another person that answered one of my topic questions in this discussion. PLEASE correct me if I am wrong on this.

[globalcompressors]

You answered your own question... 12.5 psi equals 25 degree saturated coil temperature. 25 degrees is NOT
cold enough for a box temperature of lower than.......40 degrees. So....as stated in the other posts, it sounds like
the unit is overcharged, the box has a bad seal, or maybe the compressor isn't pulling all the way down...mechanically.
Maybe a combonation of all the above. Maybe someone replaced the compressor with the incorrect one. Several
factors could be working against your project.

Go back and reread the info Yaro and myself gave you. 40 degree box = 8-10 psi.....NOT 12.5. 
30 degree box = 5 psi or so.