Danfoss · VLT HVAC Basic FC 101
The frequency converter has stopped receiving valid control word commands via its serial communication interface, leading to a timeout. This alarm is active when parameter 8-04 Control Timeout Function is not set to [0] Off. If configured to Stop and Trip, the drive will safely ramp down and then trip, indicating a loss of communication. Unresolved communication loss prevents external control of the drive.
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Verify the physical connection of the serial communication cable (e.g., RS485 A/B, Ethernet RJ45) at both the drive and the master controller.
Check drive parameters P8-00 (Protocol), P8-01 (Address), P8-02 (Baud Rate), and P8-03 (Parity) match the master controller settings.
Monitor communication activity using LED indicators on the drive's communication port or the master controller's module.
Temporarily disable the control word timeout function (set P8-04 Control Timeout Function to 'No function') for diagnostic purposes.
Use a communication diagnostic tool (e.g., Modbus RTU scanner) to test direct communication with the drive's address.