Troubleshooting by Indication on the Remote Controller Si34-603178 Troubleshooting3.41 “U4” Malfunction of Transmission between Indoor Unitsand Outdoor UnitsRemoteControllerDisplayU4ApplicableModelsAII indoor unit modelsRX(Y)MQ4~6PMethod ofMalfunctionDetectionMicrocomputer checks if transmission between indoor and outdoor units is normal.MalfunctionDecisionConditionsWhen transmission is not carried out normally for a certain amount of timeSupposedCauses Indoor to outdoor, outdoor to outdoor transmission wiring F1, F2 disconnection, short circuitor wrong wiring Outdoor unit power supply is OFF System address doesn’t match Defect of outdoor unit PC board Defect of indoor unit PC board
