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Left/Upper lamp blinking ON and OFF at 0.5-second intervals

Left/Upper lamp blinks on/off every 0.5 seconds — Indoor/outdoor unit miswiring or serial signal issue

Mitsubishi Electric · Air Conditioning

What does Left/Upper lamp blinking ON and OFF at 0.5-second intervals mean?

This indicates a problem with the connection or signal between the indoor and outdoor units. The indoor unit may not operate when the EMERGENCY OPERATION switch is pressed.

Common Causes

  • Miswiring between indoor and outdoor units
  • Trouble with the serial signal communication
  • Poor connection or damage to indoor/outdoor connecting wire

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Check the indoor/outdoor connecting wire for correct installation, damage, or loose connections.

  2. 2

    Refer to section 10-6, 'How to check miswiring and serial signal error', for detailed steps.

  3. 3

    Verify power supply to the indoor unit.

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
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