Kitchen Large Electric Appliances - Sub Zero Model 511 Freezer Problem

I have a 19yr old Sub Zero, bottom freezer model 511. The freezer failed and the compressor, dryer, cold control and defrost timer were replaced. The freezer does not work properly. It will make ice but the cubes stick together and ice cream melts and refreezes. The lowest temperature I have recorded was 2 degrees on the max setting and it rises to 20 and higher for several hours at a time. The light and heater appear to function properly. The service man has been here numerous times and has contacted Sub Zero service. The gas was replaced, pressures rechecked and compressor current draw verified. Any suggestions?

Maybe a defrost thermostat out of whack. Or a bad electrcial connection somewhere that causes the unit to not always run when it should and then shut off whenever it feels like it and start again whenever it feels like it. Or, gas pressure is NOT right, and maybe his gauges are bad, or trapped air or some clog in the lines (I'm just throwing this out there in theory as I am no refrigeration recharge person, as you have to be state certified for that), or somehow the specs for that unit are not what he thinks. It does indeed behave like low on refrigerant. When somewhat low, they can act sporadic where one minute things freeze and then on some new cycle it does not, and things thaw. Or the defrost timer or control replacement is bad. Or the defrost drainage is not occuring properly and refreezes in freezer blocking off something.

Through elimination of the electrical stuff, which surely can be done by competant repair person (WHEN THE PROBLEM IS PRESENT), he should be able to rule everything out, so that he can determine if the issue lies with the refrigerant circulation system or not.

Sticky problem. The way to find it is to use data recorders which will monitor temperatures, compressor run times and defrost run times. Ask the serviceman what the superheat and subcooling on the refrigeration system are. Looking at pressures and compressor amp draw isn't enough. No way should the temp be going up to 20 degrees and staying there. I suspect that either the wrong cold control was applied , the cold control sensing bulb is in the wrong location or the compressor is going off for long periods when it shouldn't be off. The mid range setting on the cold control should work just fine. Can you post the complete model #?

You could have an intermittant condensing fan or evaporator fan. Next time it stops, feal the compressor for overheating and verify evaporator fan is running.