I have a 12 cubic foot frost free fridge (Camco Model CRT1200VLT-1) whose freezer isn't cold enough to keep meat frozen. This is one of those GE apartment size fridges where you have to take out the freezer floor to get to the evaporator, evaporator fan, defrost heater and defrost thermostat.

I can feel a draft in the freezer compartment, so I know the evaporator fan is running. On this fridge the defrost thermostat diverts power from the cold control to the defrost heater, so if the evaporator fan is running, then the cold control is calling for cold, the evaporator fan and compressor are getting power and therefore the fridge can't be stuck in defrost mode. The compressor sounds like it's running when I use a mechanic's stethoscope on it and the line between the compressor and the condesnor coil behind the fridge is hot to the touch. Still the freezer compartment isn't getting cold enough to freeze water or keep meat frozen.

I replaced the cold control, but that didn't do any good.

Until now, this fridge would make a loud knocking sound when the compressor stopped, presumably due to a broken suspension spring inside the compressor housing. Now, the compressor and evaporator fan seem to run continuously 24/7 except for defrost cycles.

I'm coming to the conclusion that the refrigerant must have leaked out of the sealed system on this fridge, and I need to buy a new fridge.

Is there anything I might be missing? Should I get an appliance repair tech in to measure the pressure drop across the compressor to see if that really is the problem, or have I covered all the bases already and proving that it's a lack of refrigerant is just a waste of money?