Viking Oven Error Code 40: Defrost Heater Open Circuit... | appliancefaults.com

Technical Background:

The Main Control Unit (MCU) monitors the defrost circuit for proper operation. When the defrost heater circuit is open, the MCU detects a loss of voltage feedback or current flow and throws a fault code 40. This code indicates that the defrost cycle cannot complete properly. Voltage to the heater is typically 120V AC.

Symptoms:

The homeowner likely observes that the oven is displaying error code 40. They may also notice that the oven is not heating properly, or that ice is building up inside the oven cavity if it's a combination oven/microwave unit.

Possible Causes:

Defective defrost heater
Open circuit in the defrost heater wiring
Faulty defrost thermostat or sensor
Malfunctioning oven control board
Loose or corroded wire connections
Blown thermal fuse (if equipped)

Solution:

1

Disconnect power to the oven at the breaker panel (LOTO).
2

Locate the defrost heater, usually behind the rear oven panel. Access may require removing the oven from the cabinet.
3

Visually inspect the defrost heater for any signs of damage or burnout.
4

Using a multimeter, test the defrost heater for continuity. A reading of OL (open loop) indicates a faulty heater. Resistance should be around 20-50 ohms. Replace if needed.
5

Check the wiring harness connected to the defrost heater. Look for loose connections, corrosion, or damaged wires. Repair or replace as necessary, using wire nuts and electrical tape.
6

If the defrost heater and wiring are good, test the defrost thermostat (if present) for continuity when cold. It should be closed. Replace if open.
7

As a last resort, the oven control board may be defective. This requires specialized testing and may be best left to a qualified technician. Replace the board after exhausting all other possibilities. Ensure the replacement board is properly configured for the oven model.

Safety Warning:

Always disconnect power to the appliance at the breaker panel before performing any repairs. Lock Out/Tag Out (LOTO) procedures must be followed to prevent accidental energization. Some components may carry high voltage, even after the power is disconnected. Use caution when working around electrical components.

Prevention:

Periodically inspect the oven cavity for excessive ice buildup. Avoid opening the oven door frequently during the self-clean cycle. Ensure proper ventilation around the oven to prevent overheating.

Expert Tip:

Some Viking ovens have a service mode that allows you to manually activate the defrost cycle. Consult the service manual for the specific sequence of button presses to enter service mode and initiate the defrost test. This can help isolate the issue.

Frequently Asked Questions

•Where is the defrost heater located in my Viking oven model?

The defrost heater is typically located behind the rear panel inside the oven cavity. You may need to remove screws or clips to access it. Refer to your oven's service manual or a parts diagram for specific location details for your model.

•What type of multimeter should I use to test the defrost heater?

A standard digital multimeter (DMM) set to the ohms setting (resistance) is suitable for testing the defrost heater for continuity. Ensure the multimeter is properly calibrated and the test leads are in good condition.

•What is the proper resistance range for a functional defrost heater?

The resistance of a functional defrost heater typically falls within the range of 20 to 50 ohms. However, it is crucial to consult the service manual or the manufacturer's specifications for the exact resistance value applicable to your specific Viking oven model.

Viking Oven Error Code 40: Defrost Heater Open Circuit Troubleshooting

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip:

Frequently Asked Questions

•Where is the defrost heater located in my Viking oven model?

•What type of multimeter should I use to test the defrost heater?

•What is the proper resistance range for a functional defrost heater?

Related questions

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip: