E6
MrCool Communication Failure Between Indoor and Outdoor Units

Indoor unit displays E6 and does not respond properly; outdoor unit may not start.

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Loose or reversed communication wiring, Broken communication cable, Incorrect polarity on S1/S2/S3 terminals, Faulty indoor or outdoor main PCB

How to Fix / Troubleshooting

Safety first: Turn off power at both indoor and outdoor disconnects before touching wiring.

Steps:

  • Verify wiring connections: Open the electrical covers on both indoor and outdoor units. Confirm that the communication terminals (often labeled S1, S2, S3 or L, N, S) match exactly on both ends (same color to same terminal).
  • Check for damage: Inspect the communication cable along its route for cuts, crushed sections, or rodent damage.
  • Tighten terminals: Gently tug each conductor at the terminal block. Retighten any loose screws.
  • Power cycle: After corrections, restore power and wait 5–10 minutes for the system to re-establish communication.

If E6 remains: A failed indoor PCB or outdoor PCB is possible. Board diagnosis and replacement should be done by a technician.

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Repair Difficulty

Medium 3/5

Required Part

Indoor-Outdoor Communication Cable
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