Mitsubishi Air Conditioner Error U3

⚡ Quick Answer: The Mitsubishi Air Conditioner error U3 indicates a communication failure between the indoor and outdoor units, often due to an open or short circuit ... ✅ DIY Fixable

What Does Error U3 Mean?

The Mitsubishi Air Conditioner error U3 indicates a communication failure between the indoor and outdoor units, often due to an open or short circuit in the thermistor sensors, such as the discharge or shell thermistors in the outdoor unit. This error may lead to intermittent beeping sounds, a flashing display, and issues with temperature regulation, causing the system to stop operation when the fault is detected.

Common Symptoms:

  • Error U3 displayed on remote or indoor unit panel
  • System may stop operation when fault is detected
  • Temperature regulation issues or inability to maintain set temperature

Possible Causes

  • Open circuit in outdoor unit thermistor (e.g., discharge thermistor TH4 or shell thermistor TH33) (medium)
  • Short circuit in outdoor unit thermistor wiring or connector (medium)

How to Fix Error U3

DIY Fix Basic Visual Inspection and Reset

  1. Turn off and disconnect power to the air conditioner at the breaker.
  2. Visually inspect accessible outdoor unit wiring harnesses and connectors for obvious damage or loose connections.
  3. After confirming there are no visible hazards, restore power and attempt a system reset by turning the unit off, waiting ~5 minutes, then powering on.
  4. Check if the U3 error clears.

Technician Only Diagnostic Testing and Sensor Replacement

  1. Use a multimeter to measure resistance of the outdoor discharge thermistor (TH4) and shell thermistor (TH33) to confirm open/short conditions.
  2. Inspect outdoor unit sensor wiring and connectors; repair or replace damaged harnesses.
  3. Replace faulty thermistor(s) identified during diagnosis.
  4. Verify correct operation and clear U3 error after replacement.

Parts needed: Outdoor unit thermistors (e.g., TH4/TH33), Wiring harness/connectors

🛑 When to Call a Pro:
  • If you are uncomfortable working near the outdoor unit or electrical components
  • If visual inspection shows damaged wiring or components you can’t safely repair
  • If the U3 error returns after basic reset and inspection

Technical Specifications

wattage N/A
component Control Board
resistance N/A
part_number Mitsubishi 9B040000
voltage_rating 230V AC

Common Questions

What does U3 error mean on Mitsubishi Air Conditioner?

U3 error signifies a communication failure between the indoor and outdoor units, often due to thermistor issues.

Can I fix Mitsubishi Air Conditioner U3 error myself?

Yes, you can perform a basic visual inspection and reset the system after ensuring no visible hazards.

How much does it cost to fix U3 error?

Repair costs for the U3 error typically range from ¥5,000 to ¥25,000+ for parts, with labor varying by region.

When should I call a technician for U3?

Call a technician if you're uncomfortable working near electrical components or if damage is beyond your repair capabilities.

Sources & References

Data last verified: 2026-07-01

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