Sub-Zero Refrigerator Cooling Coil Frozen: Troubleshootin... | appliancefaults.com

Technical Background:

The Sub-Zero's MCU (Main Control Unit) manages the defrost cycle based on temperature sensor readings and timer settings. The MCU energizes the defrost heater, melting ice on the evaporator coil. Voltage (120V AC) is supplied to the heater through the defrost thermostat, which acts as a safety switch. Faulty components in this circuit prevent proper defrosting, leading to ice accumulation.

Symptoms:

The refrigerator section is warmer than usual, and you notice excessive ice buildup on the back wall of the freezer. Food may be spoiling prematurely. The compressor may be running more frequently than normal.

Possible Causes:

Defective defrost heater
Faulty defrost thermostat
Malfunctioning defrost timer
Damaged temperature sensor
Air leak into the refrigerator compartment
Blocked drain line

Solution:

1

Disconnect the refrigerator from the power outlet.
2

Remove the back panel inside the freezer to access the evaporator coil. Use a 1/4-inch nut driver.
3

Inspect the defrost heater for continuity using a multimeter. A reading of 20-120 ohms is typical. Replace if open.
4

Check the defrost thermostat for continuity when cold (below 40°F). It should be closed. Replace if open. Use an ice pack to chill the thermostat for testing.
5

Test the defrost timer. Manually advance the timer into defrost cycle. The heater should activate. If not, replace the timer.
6

Examine the drain line for ice blockage. Use a steamer or hot water to clear any blockage. Ensure water drains freely into the drain pan below.
7

Check door seals for air leaks. Replace if damaged. Use a dollar bill to test the seal around the door.

Safety Warning:

Always disconnect power before servicing. Lock-Out/Tag-Out (LOTO) procedures should be followed to prevent accidental energization. High voltage (120V AC) is present in the control panel.

Prevention:

Regularly clean the refrigerator interior and door seals. Ensure proper ventilation around the refrigerator. Avoid overfilling the refrigerator, which can restrict airflow.

Expert Tip:

To force a defrost cycle on some Sub-Zero models, simultaneously press and hold the “Freezer Up” and “Freezer Down” buttons for approximately 10 seconds. This will initiate a manual defrost. Consult the service manual for your specific model.

Frequently Asked Questions

•How do I access the defrost timer on my Sub-Zero?

The defrost timer is typically located behind the control panel, either in the refrigerator or freezer compartment, depending on the model. Consult your service manual for specific instructions on accessing it.

•What type of defrost heater does my Sub-Zero refrigerator use?

Sub-Zero refrigerators typically use a glass tube heater or a metal sheathed heater. The correct replacement heater will be listed in your unit's parts diagram. You can usually find this on the Sub-Zero website by entering your model number.

•How often should a Sub-Zero refrigerator defrost?

Sub-Zero refrigerators typically defrost every 8-12 hours of compressor run time. The exact frequency can vary based on usage and environmental conditions.

Sub-Zero Refrigerator Cooling Coil Frozen: Troubleshooting Guide

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip:

Frequently Asked Questions

•How do I access the defrost timer on my Sub-Zero?

•What type of defrost heater does my Sub-Zero refrigerator use?

•How often should a Sub-Zero refrigerator defrost?

Related questions

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip: