Diagnosing Sub-Zero Defrost Issues

Diagnosing defrost issues in Sub-Zero Freezers.

This is the proper procedure that will work for diagnosing your Sub-Zero Freezer that is not defrosting. This works on pretty much all Sub-Zero freezers and most household refrigerators that utilize a control board. In order to do this test you need a few tools

  1. Volt meter and non-contact meter.
  2. Philips head screw driver
  3. Needle nose pliers
  4. Blow Drier

How does your defrost system work?

Your control board gets power from the wall.

When it is time to defrost your control board sends power to the defrost heaters.

In between your heaters and your control board you have a Terminator switch which is in essence, a heat sensitive on/off switch.

When its too warm, the terminator switch opens, or turning the heaters off.

This should happen at the tail end of the defrost cycle, or if the machine is too warm to need a defrost cycle.

We need to do a few things to verify operation of this heating cycle.

Watch the video to learn how to check for power at your control board, your terminator switch, and your heaters.

Watch Our Diagnostic Video:

Extra info:

  1. A defrost cycle in a sub zero should last about 15 to 20 minutes.
  2. Frost ups dont necessarily point to a defrost fault but certainly can.\
  3. Common error codes you may encounter: EC 24 EC 21 EC40
  4. If left alone for a long time we have seen may other issues develop, including bad evaporator fans, bad ice makers, bad drain heaters even compromised sealed systems.
  5. Although this is performed on a 600 series unit the procedure is the same for 700 series units as well as BI series units. Quite honestly, this is how all appliances work to defrost the units now. Use it on any fridge.

What if i dont have a control board?

Then you have a Defrost Timer! Which is a little timer mechanism designed to send you circuit into defrost every six hours. Do the same exact procedure but treat your defrost timer like a control board!

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