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Upper lamp blinks 0.5-second ON 0.5-second OFF

Upper lamp blinking 0.5 seconds ON/OFF — Indoor and outdoor units not operating

Mitsubishi Electric · Air Conditioning

What does Upper lamp blinks 0.5-second ON 0.5-second OFF mean?

The indoor and outdoor units will not operate. This indicates the serial signal from the outdoor unit has not been received for 6 minutes. Check for wiring issues or signal interruptions.

Common Causes

  • Miswiring between indoor and outdoor units
  • Serial signal interruption
  • Outdoor unit not receiving signal

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Refer to the section 'How to check miswiring and serial signal error'.

  2. 2

    Check the compressor protector status in the outdoor unit service manual.

  3. 3

    Ensure all wiring connections are secure.

Browse all codes in this manual (170)
Verified technical data. Last updated: April 2026

Related Faults

0.5-second ON / 0.5-second OFF blinkUpper lamp blinks 0.5-second ON/OFF - Miswiring or serial signal error00Normal operation - No error codes1 beep during error display mode1 beep during error display mode - Unit has an error (different code)
Source: Mitsubishi Electric Air Conditioning
Open Manual (Page 38)Search more codes in this manual