General Assist Technical Reference

E:11 Serial Communication Error

Serial reverse transfer error - Outdoor unit
Multi Split Service Manual SR_MU006EF_06 | Revision 06 | Issue date 7 March 2025
What this error means: E:11 is generated when the indoor unit cannot receive the serial signal from the outdoor unit. The fault can be caused by a connection problem, an external electrical disturbance, an outdoor main PCB fault, or an outdoor fan motor fault.
Electrical safety: The checks below include live voltage measurements. Testing must only be carried out by appropriately qualified service personnel using suitable test equipment and safe electrical work practices.

1. Error indication

ItemIndication
Operation indicator1 flash
Timer indicator1 flash
Economy indicatorContinuous flash
Error codeE:11

Detection condition

The error is detected when the indoor unit cannot receive the serial signal from the outdoor unit for:

  • More than 2 minutes after power is switched on, or
  • More than 15 seconds during normal operation.
Detected at the outdoor unit: Main PCB / outdoor fan motor circuit.

2. Likely causes

Possible cause
Indoor-to-outdoor connection failure
External electrical noise / harmonic interference
Outdoor unit main PCB failure
Outdoor unit fan motor failure
Outdoor EEV coilk

3. Diagnostic procedure

Check point 1 - Reset the power and operate

Reset the system power and operate the air conditioner again.

Does E:11 return?

  • Yes: Continue to Check point 2.
  • No: Go to Check point 1-2 and investigate external electrical interference.
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Check point 2 - Check the connection
  • Check for loose or disconnected wiring between the indoor and outdoor units.
  • Check the control-unit connections for loose connectors, open-circuit wiring or incorrect wiring.
  • If an abnormal connection is found, correct it in accordance with the applicable installation manual or Design & Technical Manual.
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Check point 3 - Check outdoor power supply voltage

Measure the voltage at the outdoor unit power terminals L-N.

Required voltage: AC 198 V to AC 264 V
Equivalent to AC 220 V -10% through AC 240 V +10%.
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Check point 4 - Check the reverse-transfer serial signal

Measure the serial signal at outdoor unit terminals 1-3.

Normal reading: The measured AC voltage should swing between approximately AC 90 V and AC 270 V.

If the serial signal is abnormal:

  1. Check the outdoor unit fan motor.
  2. If the outdoor fan motor is abnormal, replace the outdoor fan motor and the main PCB.
  3. If the checked components are normal, replace the outdoor unit main PCB.

Check point 1-2 - External electrical interference

  • Check the integrity and insulation of the grounding system.
  • Check for equipment near the power cable that may generate harmonic interference, such as neon lighting or other electronic equipment.

4. Quick diagnostic summary

CheckExpected result / action
Power resetIf the fault does not return, investigate grounding and electrical noise.
Interconnection wiringNo loose connectors, open circuits or mis-wiring.
Outdoor L-N voltageAC 198-264 V.
Outdoor terminals 1-3Serial signal should swing between AC 90-270 V.
Outdoor fan motorIf abnormal, replace the fan motor and main PCB.
EEV
Check for shorts and open circuits. If short or open, replace EEV coil and main PCB
All checks normal but fault remains
Replace the outdoor unit main PCB.
Important: Do not replace components solely from the error code. Complete the connection, supply-voltage and serial-signal checks before condemning the outdoor PCB or fan motor.
Source: AIRSTAGE Multi Split Service Manual SR_MU006EF_06, Revision 06, issued 7 March 2025 - Troubleshooting with error code, E:11 Serial communication error (Serial reverse transfer error) (Outdoor unit).