What It Means
Outdoor defrost temperature sensor hardware fault.
York All Systems
York Error Code F21
Troubleshooting guide for the York system fault F21.
Possible Causes
- Defrost temperature sensor open, shorted, or out of range.
- Damaged, loose, or corroded sensor wiring harness.
- Outdoor control board sensor circuit malfunction.
Not sure which one it is — or if it's none of these? Try ACLogics today.
Disclaimer: This information is for general reference. Error codes can vary by model and production year. Always refer to your machine's specific manual and the information printed on the unit itself.
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Full Diagnosis
Defrost temperature sensor failure.
All Recorded Causes
Verify Before Replacing Parts
- Confirm the exact York model family and default context before acting on a generic code description.
- Verify the sensor or thermistor reading against the expected range for the current operating condition, keeping in mind that the most likely cause listed above.
- Check the sensor harness and board connection before condemning the sensor itself; on York units this is also where you'd confirm the next candidate on the list.
- After the correction, run the system long enough to confirm the default fault does not return under normal load.
Not sure which system this York code is on?
ACLogics has guided diagnostics for 60 York fault codes and asks the right questions to narrow it down.
