Sub-Zero UC-24 Code 06: refrigerator evaporator sensor issue

What 06 means

Code 06 on a legacy UC-24 undercounter unit, such as the UC-24C or UC-24R, means the refrigerator evaporator thermistor read open, was shorted for 10 or more seconds, or gave readings that did not agree with each other. The control uses this sensor to judge when the cooling coil needs defrost and when it is cold enough. The 600 and 700 Series built-ins share this numbering but keep a separate chart, so the two should not be mixed. Common signs are frost building on the back wall or uneven cooling.

Common causes of 06

A disconnected or corroded evaporator sensor plug
Sensor wiring damaged near the evaporator or by ice buildup
An evaporator thermistor that no longer reads correctly
A control board that misreads the sensor input

✓ One safe check you can try

1. Look through the interior for heavy frost on the rear panel. 2. Check the door gasket for gaps that let humid air in. 3. Remove items that block air circulation at the back. 4. Turn the unit off at the breaker for one minute, then back on. 5. If frost keeps growing or 06 comes back, schedule service.

! Why to stop there

The evaporator sensor sits behind the rear panel near the cooling coil
Chipping ice off the coil can puncture refrigerant tubing
Testing the sensor means reading resistance at a known temperature

Opening a panel yourself does not automatically cancel a manufacturer warranty, but it can cause accidental damage, and some manufacturers set their own service conditions. Check your warranty terms, or ask us, before deciding.

→Same appliance

Other Undercounter & Drawers codes

05Sub-Zero UC-24 Code 05: refrigerator cabinet sensor reading 07Sub-Zero UC-24 Code 07: freezer cabinet thermistor reading 08Sub-Zero UC-24 Code 08: freezer evaporator thermistor 22Sub-Zero UC-24 Code 22: no defrost voltage feedback 23Sub-Zero UC-24 Code 23: defrost overheat without feedback 50Sub-Zero UC-24 Code 50: refrigerator compressor runs too long 21Sub-Zero UC-24 Undercounter Code 21: defrost overheat EE + Service flashingSub-Zero UC-24 Undercounter EE with "Service" Flashing: temperature sensor problem

0606 questions

Why is there frost on the back wall of my UC-24C?

The control relies on the evaporator sensor to start and end defrost. With a bad reading, defrost may not run when it should, so frost builds on the coil and spreads to the rear wall.

Can I defrost it myself?

You can unplug it and let it thaw with towels down, which may help for a few days. The code will return until the sensor or wiring is fixed, so plan a repair.

How do you fix it?

We check the plug, trace the wire and measure the sensor, then quote in writing before replacing anything. Work is covered by our 30-day workmanship warranty.