Some Sub Zero refrigerators have electronic control boards, actually most modern Sub Zero refrigerators do. The control board on the refrigerator does a lot. The control board tells the compressor when to come on, sends voltage to the lights fans, so on and so forth. If the refrigerator has an internal problem, Sub Zero has the logic in the board programmed to display an error code in the digital read out. One of the more common Sub Zero refrigerator code is error code 50. The code 50 means excessive compressor run time, more often than not resulting from a leaking evaporator. Unlike most residential refrigerators, Sub Zero uses two compressor and two evaporators. This means that if one side stops cooling it wont affect the other side (refrigerator side and freezer side).
The first thing that needs to be done is to examine the evaporator itself. The back panel needs to be removed to have a look at the coils. The coils should have 1/16 frost from top to bottom. In most cases with this error code, the evaporator will only have frost in the upper left corner, this means you have a freon leak.
Finding the coils with a full frost pattern would indicate a dirty condenser or failed condenser fan motor. Several other things can cause this issue and tests would need to be made to determine the exact failure. If needed, we would be happy to assist you. Sub Zero refrigerators can be simple to work on; we know these units well and can answer or review any question you have