Frost continually forms on the back wall of our Sub Zero Refrigerator - Model 501R. How can I fix this problem?

Frost continually forms on the back wall of our Sub Zero Refrigerator - Model 501R. How can I fix this problem?

It seems your automatic self defrost system is not working. If you have the proper tools and a wiring diagram test the following. Defrost timer,defrost heater, and the defrost bi-metal/defrost termination thermostat. The heater and defrost bi-metal/termination stat will be located inside the refrigerators freezer compartment behind the evaporator wall cover panel inclosure. I do not know where the defrost timer is located on your model number machine but it should show on the wiring diagram.

Here are the service manuals to help you fix the defrost system:
http://dl.dropbox.com/u/8010163/Sub_Zero_600_Series_refrigerator.pdf
http://dl.dropbox.com/u/8010163/Sub-Zero_500_series_refrigerator.pdf
http://dl.dropbox.com/u/8010163/Whirlpool%204322537A%20How%20to%20use%20Test%20Equ ipment%20Service%20Manual.pdf
You will need a good digital meter which you can buy at any hardware, building supply, or Radio Shack store.

Here are the service manuals to help you fix the defrost system:
http://dl.dropbox.com/u/8010163/Sub_Zero_600_Series_refrigerator.pdf
http://dl.dropbox.com/u/8010163/Sub-Zero_500_series_refrigerator.pdf
http://dl.dropbox.com/u/8010163/Whirlpool%204322537A%20How%20to%20use%20Test%20Equ ipment%20Service%20Manual.pdf
You will need a good digital meter which you can buy at any hardware, building supply, or Radio Shack store.

Hi drtom444,
I am wondering if you can share with me the installation instruction of Subzero 561 thermostat (4201260). I removed it, it has two capillaries with one bulb. I would like to know where and how long they goes into the evaporator.
I appreciate

kudus

They have to match the old t-stat. If the old t-stat had 10 inches going into evaporator then the new one has to be the same way with the excess coiled up (without any sharp bends) and placed behind new one. The new one must be in exactly the same place. I have never seen one with two capillary tubes in my 35 years in refrigeration work, but anything is possible. Make sure the electrical leads are well insulated and have no contact with capillary tube or it will ruin the t-stat at once.