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Error code · Microwave

Code 4d21 on Whirlpool Built-In Microwaves: Cooling Fan and Airflow Too Slow

Code 4d21 on Whirlpool built-in microwaves and microwave drawers, including the WMC50522AS, means the cooling fan speed is too low. The listed areas to check are an airflow restriction, the oven cooling fan, or the wiring…

Medium · inspection needed
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Code
4d21
Appliance
Microwave
Brand
Whirlpool
Warranty
30-day workmanship

What 4d21 means

Code 4d21 on Whirlpool built-in microwaves and microwave drawers, including the WMC50522AS, means the cooling fan speed is too low. The listed areas to check are an airflow restriction, the oven cooling fan, or the wiring connected to it. A fan that cannot move enough air lets the oven run hotter than intended, so the oven shows the code and may stop heating to protect itself.

Common causes of 4d21

  • Airflow restriction at vents or around the installation
  • Oven cooling fan running slower than the control expects
  • Wiring or connector to the fan
  • Brief condition that a power cycle removes
✓ One safe check you can try

1. Check that vents and the space around the microwave are not blocked by items or dust. 2. Flip the breaker off and wait a minute. 3. Turn it back on. 4. Watch the oven for one minute to see whether 4d21 comes back. 5. Finish by running a short cooking cycle.

! Why to stop there
  • If 4d21 returns with the vents clear, we test the fan speed and its wiring
  • A fan that spins can still be too slow, so we measure rather than listen
  • Price in writing first, and workmanship covered for 30 days
Opening a panel yourself does not automatically cancel a manufacturer warranty, but it can cause accidental damage, and some manufacturers set their own service conditions. Check your warranty terms, or ask us, before deciding.
→Same appliance

Other Microwave codes

Feature Not Available or Fault DetectedWhirlpool Built-in Microwave Message "Feature Not Available": Retry or Cut Power LOCWhirlpool Microwave LOC on the Display: Control Lock Is On PFWhirlpool Over-the-range Microwave Showing PF: Power Failure Indicator Press Cancel to ResetWhirlpool Built-in Microwave Message "Press Cancel to Reset": Error Cleared by Cancel F8 E4Whirlpool Microwave Drawer Error Code F8 E4: Exhaust Air Temperature Sensor Probe or Insert ProbeWhirlpool Built-in Microwave Asking for "Insert Probe": Seat the Meat Probe F8E5Whirlpool Microwave Code F8E5: Exhaust Air Temperature Sensor PUSH or PSHWhirlpool Built-in Microwave Shows PUSH or PSH: Press Start
4d214d21 questions
How do I know the cooling fan is slow?

You often cannot hear much difference. The oven measures fan speed and posts 4d21 when it is too low. We check the fan and the airflow path to find the cause.

Can a blocked vent cause 4d21?

Yes. Restricted airflow is one of the listed areas. Clear any obstruction around the oven, do the one-minute breaker reset, and see if the code stays away.

Is an older microwave drawer worth a fan repair?

Often yes. Older built-ins are still common in Houston, and a fan repair is usually modest compared with a new unit. We say plainly if it is not worth it.

Book a visit

Still seeing 4d21?

A technician diagnoses it on site and gives you the price in writing before any work starts.

(713) 589-6107