Microwave displays F3 and may shut down or refuse to start.

Safety First: Disconnect power. Internal components can carry lethal voltage even when unplugged; do not touch the high-voltage section.

Inspection steps:

• Locate the temperature sensor: On many Frigidaire microwaves, the cavity temperature sensor (thermistor) is mounted inside the oven cavity wall or on the top/side behind the interior liner.
• Check wiring: With power off, remove the outer cabinet (screws at back and sides). Carefully locate the sensor and follow its wires to the control board. Look for burnt, pinched, or broken wires.
• Check connections: Reseat the sensor connector at both the sensor and the control board.
• Test sensor (advanced): Using a multimeter, measure resistance across the sensor leads. Compare to Frigidaire service specs (typically several kΩ at room temperature). An open or shorted reading indicates a bad sensor.
• Replace faulty part: If the sensor is defective, replace the Frigidaire cavity temperature sensor / thermistor. If the sensor tests good but F3 persists, the main control board may need replacement.

Note: Removing the outer cabinet exposes high-voltage components. If you are not experienced, have a professional perform this repair.