Maytag Refrigerator: Defrost Heater vs. Defrost Timer... | appliancefaults.com

Technical Background:

Many Maytag refrigerators use a defrost system with a defrost heater, defrost thermostat, and a defrost timer (or an electronic control board). The timer or board activates the defrost heater for a short period (typically 20-30 minutes) to melt any frost buildup on the evaporator coil. The defrost thermostat acts as a safety switch, preventing the heater from overheating. The MCU (Main Control Unit) controls the defrost cycle based on temperature sensors and pre-programmed algorithms. Voltage is supplied from the breaker panel through the refrigerator wiring to the defrost components. Failure of any of these components can disrupt the defrost cycle.

Symptoms:

The refrigerator is not cooling properly, and ice is building up on the back wall of the freezer. Food in the freezer may be thawing and refreezing. The refrigerator may be running constantly.

Possible Causes:

Failed defrost heater
Defective defrost timer (or electronic control board relay)
Open defrost thermostat
Wiring issue in the defrost circuit
Faulty Main Control Board (MCU)

Solution:

1

Unplug the refrigerator or turn off the breaker at the breaker panel.
2

Locate the defrost heater, usually behind the evaporator coil in the freezer. It might be a glass tube or a metal-sheathed heater.
3

Disconnect the wires to the defrost heater.
4

Use a multimeter set to ohms (resistance) to test the heater. A good heater should show some resistance (typically 20-120 ohms). If it reads open (OL), the heater is bad.
5

Locate the defrost timer (if applicable – some models use an electronic control board instead). If it's a mechanical timer, manually advance it into defrost mode. If you have an electronic control board, consult the service manual to initiate a manual defrost cycle through the service mode.
6

With the refrigerator plugged back in (carefully!), use a multimeter to check for 120V AC at the defrost heater terminals during the defrost cycle. If voltage is present, but the heater isn't working, the heater is the problem. If no voltage is present, the timer (or electronic control board) or defrost thermostat is suspect.
7

If the timer or electronic board is suspected, confirm proper operation following service manual instructions. Use a 1/4-inch nut driver or 5/16-inch socket to access components.

Safety Warning:

Always disconnect power to the refrigerator before attempting any repairs. Lock Out / Tag Out (LOTO) procedures should be followed. High voltage (120V AC) is present in the appliance. Exercise extreme caution.

Prevention:

Periodically check the refrigerator for proper cooling. Avoid overfilling the freezer, which can restrict airflow and contribute to frost buildup. Vacuum the condenser coils every 6 months to improve efficiency and reduce stress on the components. Replace the water filter regularly.

Expert Tip:

On many electronic control board models, you can force a defrost cycle by pressing and holding the freezer temperature UP and refrigerator temperature DOWN buttons simultaneously for 10 seconds. Refer to the service manual for your specific model to confirm the correct service mode sequence.

Follow-up Questions:

Frequently Asked Questions

•How do I test the defrost thermostat?

The defrost thermostat should be closed (0 ohms) when cold (below 40°F) and open (OL) when warm. You can test it by placing it in a cup of ice water for a few minutes and then checking for continuity with a multimeter.

•Where is the defrost timer located?

On older models, the defrost timer is usually located behind the control panel, either inside the refrigerator compartment or behind the kick plate at the bottom front of the refrigerator. Some electronic models do not have a physical timer; the function is controlled by the main control board (MCU).

•What if the defrost heater has continuity, but still doesn't work?

Even with continuity, the heater element could be internally damaged and not producing enough heat. Also, ensure you're getting the proper voltage (120V AC) to the heater during the defrost cycle. A low voltage reading can indicate a problem with the wiring or the control board.

Maytag Refrigerator: Defrost Heater vs. Defrost Timer Troubleshooting

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip:

Frequently Asked Questions

•How do I test the defrost thermostat?

•Where is the defrost timer located?

•What if the defrost heater has continuity, but still doesn't work?

Related questions

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip: