The Modbus client function includes the following two:
- 1-to-1 Modbus/VRF gateway with Modbus client function (usually customized product by gateway suppliers)
- 1-to-n Modbus/VRF gateway with Modbus client function or an additional Modbus client unit
The Modbus client manages communication between VRF HMI units (server function) and the Modbus gateway to ensure proper operation. When using a Modbus gateway without Modbus client function, an additional Modbus client unit is required.
RDF280.V.. does not have termination resistor.
For VRF systems with multiple indoor units
If its VRF outdoor unit (2-pipe system) can only support either heating or cooling control sequence each time, only Modbus client or VRF HMI units selected as Client unit can select the fixed heating or cooling control sequence for the VRF system.
- When heating mode is selected, the Modbus client also sets P01 of each connected VRF HMI server unit = 4 (HEAT/FAN) only.
- When cooling mode is selected, the Modbus client also sets P01 of each connected VRF HMI server unit = 5 (COOL/FAN/Dehumidification) or 6 (COOL/FAN) depending on VRF operating modes supported by the indoor units.
If, e.g., heating is selected, RDF280.V.. can only select VRF operating modes: HEAT or FAN. If cooling is selected, RDF280.V.. can only select VRF operating mode: COOL, FAN or Dehumidification.
If a VRF outdoor unit (4-pipe system) allows both heating and cooling control sequences selected by individual indoor units, each connected VRF HMI unit can be preset with P01 = 0, 1, 2 or 3 according to the VRF operating modes supported by the indoor and outdoor units. Note that some indoor units do not support AUTO or Dehumidification.