Fujitsu Mini-Split Error Code 39: How to Fix It

Medium 30-60 minutes Medium Severity Verified June 2026
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Error Code
39
Brand
Fujitsu
Product Type
mini_split
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
30-60 minutes
Error code 39 on your Fujitsu mini-split indicates a fault with the outdoor unit's air thermistor (temperature sensor). This sensor measures the outdoor ambient temperature and helps the system regulate operation. When it fails, the unit may not cool or heat properly, or it may stop running altogether.
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Tools You'll Need

How to Fix Error Code 39

  1. Turn Off Power and Safety Check

    Always disconnect power before servicing. Capacitors can hold dangerous voltage even when off.

  2. Locate the Air Thermistor

  3. Check Thermistor Resistance

    Handle thermistor carefully; it is fragile.

  4. Inspect Wiring and Connections

  5. Replace the Faulty Thermistor

    Use only a Fujitsu-approved replacement thermistor to ensure correct temperature calibration.

  6. Reassemble and Test

    If the error returns, the control board may be faulty; contact a professional technician.

Parts You May Need

Outdoor air thermistor
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Outdoor air thermistor
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Outdoor air thermistor
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Outdoor air thermistor
Check Price on Amazon
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When to Call a Professional

If replacing the thermistor does not clear error code 39, the issue may be with the control board or a wiring harness fault. A professional HVAC technician can diagnose and repair these complex components safely.

Frequently Asked Questions

Can I bypass the thermistor to clear error code 39?
No. Bypassing the thermistor is not recommended and can cause system damage or safety hazards. Always replace the faulty sensor.
How much does a Fujitsu mini-split air thermistor cost?
A replacement air thermistor typically costs $20–$50. Ensure you get the correct part for your specific model.
Will error code 39 make my mini-split stop working?
Yes, the system may stop cooling or heating, or run inefficiently. It's important to address the fault promptly.
Can a dirty outdoor coil cause error 39?
No, a dirty coil typically causes different error codes. However, cleaning the coil is good maintenance and can prevent other issues.
Do I need to vacuum the refrigerant after replacing the thermistor?
No, replacing the thermistor does not involve the refrigerant circuit. No vacuuming or refrigerant handling is required.

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