Mitsubishi Mini-Split Error Code U3: How to Fix It

Medium 30-60 minutes Medium Severity Verified June 2026
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Error Code
U3
Brand
Mitsubishi
Product Type
mini_split
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
30-60 minutes
Mitsubishi mini-split error code U3 indicates an open or faulty outdoor coil thermistor. This sensor monitors the temperature of the outdoor unit's coil, and when it fails, the system may stop cooling or heating. This guide will help you diagnose and replace the thermistor.
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Tools You'll Need

How to Fix Error Code U3

  1. Turn Off Power and Safety First

    Always disconnect power before opening the unit. Capacitors can hold dangerous voltage.

  2. Locate the Outdoor Coil Thermistor

  3. Test the Thermistor with a Multimeter

    Do not touch the probes to live circuits.

  4. Replace the Faulty Thermistor

    Ensure correct polarity if applicable, though typically non-polarized.

  5. Clear the Error Code and Test

Parts You May Need

10kΩ NTC Thermistor (Outdoor Coil Sensor)
Check Price on Amazon
10kΩ NTC Thermistor (Outdoor Coil Sensor)
Check Price on Amazon
10kΩ NTC Thermistor (Outdoor Coil Sensor)
Check Price on Amazon
10kΩ NTC Thermistor (Outdoor Coil Sensor)
Check Price on Amazon
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When to Call a Professional

If replacing the thermistor does not clear the error, or if you are uncomfortable working with high-voltage components, contact a certified HVAC technician.

Frequently Asked Questions

Can I run my Mitsubishi mini-split with error code U3?
It is not recommended. The system may not heat or cool properly and could cause further damage. It's best to fix the issue promptly.
What is the typical resistance of a Mitsubishi outdoor coil thermistor?
At room temperature (77°F), a 10kΩ NTC thermistor is commonly used. Resistance decreases as temperature rises.
Where can I buy a replacement thermistor?
You can purchase a generic 10kΩ NTC thermistor online (Amazon, HVAC supply stores) or an OEM part from Mitsubishi dealers.
Is error code U3 serious?
It is a medium-severity error. It will disable the system until repaired, but it does not typically indicate a major failure.
Do I need to replace the entire outdoor coil?
No, only the thermistor sensor needs replacement. It is a small, inexpensive part.

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