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Error code reference

KitchenAid Microwave Error Code FDE3

Hood Fan relay failure.

KitchenAid codesKitchenAid microwave codes

Hood Fan relay failure.

First step from the service manual

Unplug microwave oven or disconnect power. Replace ACU.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What FDE3 means on a KitchenAid microwave

The FDE3 error code on a KitchenAid microwave indicates a hood fan relay failure. The hood fan relay is a component within the Appliance Control Unit (ACU) that switches power to the ventilation fan motor. When the control board commands the fan to run, it energizes this relay. If the relay fails to close, fails to open, or produces a feedback signal outside expected parameters, the control logic flags FDE3 to indicate the relay circuit is not functioning correctly.

The ACU is the central control board that manages all major microwave functions, including the hood fan relay output. A relay failure can result from a welded or stuck relay contact, a failed relay coil, or internal PCB damage such as burnt traces or a failed driver transistor on the control board. In some cases, an overloaded fan motor can draw excess current that damages the relay over time. The failure may present as a fan that runs continuously, a fan that will not run at all, or an error displayed at startup during self-diagnostics.

The specified first diagnostic step is to unplug the microwave or disconnect power, then replace the ACU. This approach reflects that the relay is integrated into the control board rather than being a standalone serviceable component. Because the relay is part of the ACU assembly, individual relay replacement is generally not a supported repair path. Technicians should confirm power is fully disconnected before accessing the control board, as microwave capacitors can retain a dangerous charge even after unplugging.

Source: manufacturer service documentation.

Common causes of FDE3

  1. 01

    Failed ACU relay

    Part replacement

    The relay on the Appliance Control Unit responsible for switching the hood fan has failed internally, either stuck open or stuck closed. This is the primary cause identified for FDE3 and requires ACU replacement.

  2. 02

    Burnt or damaged PCB traces on the ACU

    Part replacement

    Overheating or electrical surges can damage the printed circuit board traces or driver components near the relay circuit. This damage prevents the relay from receiving or completing proper switching signals.

  3. 03

    Fan motor overload damaging the relay

    Part replacement

    A seized or failing hood fan motor can draw excess current through the relay contact over time, causing the relay to overheat and weld shut or fail open. Inspect the fan motor for free rotation and check for obstructions.

  4. 04

    Intermittent wiring connection to the ACU

    Wiring / connection

    A loose or corroded connector between the ACU and the fan motor circuit can produce erratic relay feedback signals, triggering the error code. Inspect harness connectors at the control board for corrosion or backed-out terminals.

See the test procedure for each cause

Frequently asked questions about FDE3

What does FDE3 mean on a KitchenAid microwave?
FDE3 indicates a hood fan relay failure. The relay that controls power to the ventilation fan motor, located on the Appliance Control Unit, is not functioning as expected. The control board detects that the relay circuit is outside normal operating parameters and displays this code to alert the user or technician to the fault.
Can I fix a KitchenAid microwave FDE3 error myself?
The repair requires replacing the Appliance Control Unit, which involves accessing internal components of the microwave. Microwave capacitors can retain a lethal electrical charge even when unplugged, so full discharge of the capacitor is critical before any internal work begins. Technicians comfortable with appliance electronics can complete this repair, but inexperienced DIYers should consider professional service due to the high-voltage hazard.
Is it safe to use my microwave when it shows the FDE3 code?
Operating the microwave with an active FDE3 error is not recommended. The ventilation fan may not function correctly, which can allow heat and steam to build up improperly during cooking cycles. Continued use with a known relay failure can also place additional stress on other components of the control board.
Will unplugging and resetting the microwave clear the FDE3 code?
A power reset may temporarily clear the error display, but because FDE3 points to a hardware relay failure within the ACU, the code is likely to return once the microwave runs its diagnostics again. A reset does not repair the faulty relay or control board. Permanent resolution requires ACU replacement.
How much does it cost to repair a KitchenAid microwave with an FDE3 error?
Repair costs vary depending on the specific model and whether you use a professional technician or source parts yourself. ACU replacement parts typically range from $100 to $250 or more depending on the model, and professional labor adds additional cost. In some cases, if the microwave is older or the part cost is high relative to the appliance value, replacement of the unit may be worth considering.

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