What does Mitsubishi Electric U1 mean?

The outdoor unit's high-pressure switch (63H) has tripped because refrigerant pressure on the discharge side rose above its safe limit, so the compressor was stopped to protect the system.

What does Mitsubishi Electric U2 mean?

The discharge temperature at the compressor outlet climbed too high, which the control reads as overheating from a shortage of refrigerant. The compressor is stopped and U2 appears on a blinking display.

What does Mitsubishi Electric U3 mean?

The control has detected an open or short circuit in the discharge-temperature thermistor (TH4, TH33) on the outdoor unit. Because the controller can no longer trust the discharge temperature reading, it stops the compressor and shows U3 on a blinking display.

What does Mitsubishi Electric error code E6 mean?

E6 on Mitsubishi Electric split systems and City Multi VRF indicates a communication fault between the indoor and outdoor units. Check the inter-unit wiring on the S1, S2, S3 terminals (S1=common, S2=power, S3=signal). Verify correct polarity and check for damaged cable insulation. Also confirm the outdoor unit has power before the indoor unit is tested.

How do I put a Mitsubishi Electric City Multi system into service mode?

To enter service mode on a Mitsubishi City Multi outdoor unit, press and hold the SW01 (check/test) button on the main PCB for 5 seconds. In service mode, you can view refrigerant temperatures, pressures (if sensors fitted), expansion valve positions, and operating frequencies on the PCB LED display. Use the Mitsubishi G-50A or AE-200 central controller for comprehensive system diagnostics.

How do I check the refrigerant charge on a Mitsubishi Electric VRF system?

Mitsubishi Electric VRF systems require precise refrigerant charge per the installation manual based on pipe lengths and number of indoor units. Use the Mitsubishi charge calculator to determine the correct charge for your system configuration. Connect low-side and high-side gauges to the service ports, operate in cooling mode at full load, and verify pressures and subcooling/superheat against the Mitsubishi target values at the current outdoor temperature.

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By Octavian Ghindea

Co-founder & CTO · Reviewed July 2026

What error codes does Mitsubishi Electric display?

Abnormal high pressure (63H worked)

Abnormal high discharge temperature, shortage of refrigerant

Open/short circuit of discharge thermistor (TH4)(TH33)

Open/short of outdoor unit thermistors (TH3, TH32, TH6, TH7 and TH8)

Abnormal temperature of heatsink

Abnormality of power module

Abnormality of superheat due to low discharge temperature

Abnormality in outdoor fan motor

Overheat protection

Abnormal pressure of 63HS

Compressor overcurrent interruption (When Comp. locked)

Current sensor error

Common questions about Mitsubishi Electric equipment

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