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Frigidaire Microwave F9 — Door switch / monitor switch fault

Frigidaire Microwave · Error code F9

What F9 Means

F9 indicates the control sees a mismatch between the primary, secondary, and monitor door switches. This is a safety-critical fault — the microwave will not start until resolved.

Symptoms

  • F9 on display
  • Microwave will not start with door closed
  • Display reads PF/F9 after door slam
  • Blown line fuse in some cases

Common Causes

1
Failed interlock or monitor switch

One of three switches stuck open or closed.

2
Bent door / misaligned latch

Hinge sag prevents simultaneous switch actuation.

3
Blown line fuse (after monitor trip)

A primary stuck closed when door opened blows the line fuse — replace switches AND fuse.

How to Fix It

  1. Unplug the microwave.
  2. Open and close the door slowly — watch/listen for clean click of all three switches.
  3. Remove the control panel/grille; ohms-test each interlock for proper open/close with door action.
  4. Replace any switch that does not actuate cleanly.
  5. Check the inline ceramic line fuse — if blown, replace it AND replace all three door switches as a set (monitor trip damages them).
  6. Verify door alignment and latch hook engagement; adjust hinges if needed.

Parts You May Need

If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.

Common replacement Microwave door interlock switch kit View on Amazon→ Common replacement Microwave ceramic line fuse 20A View on Amazon→

More Frigidaire Microwave Codes

Child Lock 'Lock' / 'L' — Child lock engaged Cooling Fan 'Cooling Fan' / Fan-runs-after-cooking — Vent fan stuck on Demo 'Demo' / 'd' — Showroom demo mode on door 'door' message — Door not fully closed F1 F1 — Control board / thermistor open F10 F10 — Analog-to-digital / keypad communication error

All Frigidaire codes → All microwave codes →

Verified against manufacturer documentation: frigidaire.com

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician.