1. Required Modbus Interface

Important: For integration of the VRF network, use the UTY-VMGX. The UTY-VMSX is a different interface and must not be treated as an equivalent replacement.

2. How the Modbus Connection Works

The UTY-VMGX operates as an interface between the external Modbus master and the VRF transmission network.

The converter receives commands from the Modbus network and transfers supported commands to the VRF equipment. It also makes supported equipment status information available for BMS monitoring.

3. System Connection Limits

These are the published connection limits. The actual project design must also comply with the VRF network, wiring, addressing and device limitations.

4. Electrical and Communication Connections

The UTY-VMGX has separate connections for the power supply, Modbus network and AIRSTAGE VRF transmission network.

Communication Switches

The manual identifies the following switches on the UTY-VMGX circuit board.

The project BMS settings and UTY-VMGX settings must match. Confirm the required baud rate, parity, stop bits and slave address using the converter installation manual and the BMS design documentation. The V-IV design manual identifies the relevant switches but does not provide a complete switch-position configuration table in this section.

5. Available BMS Control Functions

The following functions are identified in the manufacturer's control and monitoring tables. Availability depends on the system configuration and installed equipment.

Indoor Unit Control

System and Outdoor Unit Control

• System time-setting command.
• Emergency stop command.
• Outdoor unit low-noise setting.
• Outdoor unit capacity-limit setting.

6. Available BMS Monitoring Functions

The converter can provide supported monitoring information including:

• Indoor-unit On/Off status.
• Operating-mode status.
• Temperature setpoint status.
• Room temperature.
• Airflow and louvre status.
• Remote-controller restrictions.
• Indoor-unit error-code status.
• Defrost, oil recovery and pump-down status.
• Indoor-unit maintenance and emergency-stop status.
• Outdoor-unit low-noise status.
• Outdoor-unit capacity-limit status.
• Outdoor-unit error-code status.
• Converter communication settings, model and software version.

For exact registers, supported values, scaling, read/write permissions and Modbus function details, use the manufacturer's UTY-VMGX interface specification. The VRF design manual provides the available functions but is not a complete Modbus register map.

7. Registering Indoor and Outdoor Unit Addresses

The manual identifies three registration methods.

Method 1 – Default Addresses

Where the documented default indoor and outdoor network addresses are used, initial address registration is not required.

The published default address ranges are:

• Indoor units: [00-00] to [00-63] and [01-00] to [01-63].
• Outdoor units: [00-00] to [00-03] and [01-00] to [01-03].

If the actual system addresses differ, use a supported registration method rather than assuming that the default address allocation applies.

Method 2 – Automatic Network Scan

1. Confirm the VRF network is correctly installed and addressed.
2. Turn on the converter's scan-setting switch (SET2-4).
3. Confirm that the scan indication appears on the LED display.
4. Wait for the converter to complete its scan and display the number of connected indoor units.
5. Turn off the scan-setting switch.
6. Confirm that the address-update indication is displayed.
7. Restart the main power using the approved isolation and restart procedure.
8. Confirm that address rewriting and synchronisation are completed.

If a scan error occurs, investigate the network and repeat the scan.

Method 3 – PC Registration

The supplied converter setup tool can also be used to register the network address information.

1. Install the converter setup software on a compatible computer.
2. Connect the computer to the UTY-VMGX using the supplied USB cable.
3. Place the converter in USB mode.
4. Configure the indoor and outdoor unit address information using the converter setup tool.
5. Select the software registration function to write the information to the converter.
6. Confirm successful registration before proceeding with BMS commissioning.

Note: The manual references a supplied DVD and legacy Windows software requirements. Confirm availability and compatibility of the current setup tool before attending site.

8. Commissioning Checklist

1. Confirm that the installed interface is the correct UTY-VMGX converter.
2. Check converter power supply and fuse.
3. Verify the VRF network wiring and connection to the correct terminals.
4. Check Modbus communication wiring and the relevant termination settings.
5. Confirm the converter address and Modbus slave address are appropriate for the installation.
6. Confirm baud rate, parity and stop-bit settings match the BMS.
7. Confirm indoor and outdoor VRF address information is correctly registered.
8. Verify that the expected number of indoor units is recognised.
9. Test an approved individual indoor-unit On/Off command.
10. Verify operating mode and setpoint command response.
11. Confirm that indoor-unit status and room temperature are reported correctly.
12. Verify alarm and fault reporting where practical.
13. Confirm scheduled commands and local-controller restrictions behave as designed.
14. Record all communication settings and commissioning results.

9. Important BMS Command Timing Restrictions

The manufacturer also specifies that forced thermostat OFF instructions must be issued by only one controlling device per refrigerant system. Multiple devices issuing these instructions may cause the system to respond incorrectly or malfunction.

10. Modbus Troubleshooting

11. Information to Provide to Technical Support

When escalating a Modbus communication issue, provide:

• VRF outdoor-unit models and refrigerant system addresses.
• Number of indoor and outdoor units installed.
• UTY-VMGX converter address and Modbus slave address.
• Baud rate, parity and stop-bit settings.
• Details of the BMS manufacturer and controller.
• Photographs of the converter PCB switch positions and wiring.
• Confirmation of the VRF address registration or scan result.
• Details of the failed command or monitoring point.
• Any displayed error codes or LED indications.
• Results of communication and control tests already completed.

GENERAL AIRSTAGE | Technical information for qualified installers, commissioning personnel and BMS integrators. Follow the equipment-specific installation documentation and applicable electrical regulations.