Hello and thankyou for using this service.can you tell me where the frost is building up on your refrigerator?Is it on the left side about 15" up from the bottom?
This is a common problem on your model Subzero. What is happening is , the unit is loosing freon and it is running continuously causing the frost to build up in that area. You can confirm it by removing the food and shelves from the fridge and taking off the back panel inside the food section. When you get the back off, you will see the evaporator coil and it will be frosted only on a small portion. That area will correspond to where you are seeing the frost build up on the front side of the panel.The problem is a serious problem that can only be fixed by replacing the leaking evaporator coil behind the panel. This is a job that will require the services of a refrigeration tech and you will need specialized tools to cut out and reweld a new coil back into the fridge and recharge the freon system
Here is a picture of what is happening
If you dont have any other questions, would you please "rate" my answer as positive for my help tonight?Thanks for the opportunity to help you.
This is a repairable thing. I have done many of them. vs the cost to replace the fridge.