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MelcoBEMS Mini (A1M)
Controls Mitsubishi HVAC units via MelcoBEMS Mini (A1M) Modbus interface
This template connects to the Mitsubishi MelcoBEMS Mini (A1M) Modbus RTU interface. It provides read and write access to HVAC parameters such as room temperature, setpoint, fan speed, air direction, drive mode, and on/off control.
- Protocol
- Modbus RTU
- Connection
- RS485, 9600 baud
- Registers
- 6, read and write
- Brand
- Mitsubishi
- Key readings
- Room Temperature · Drive Mode · Temperature Setpoint · Fan Speed · Air Direction · Drive On/Off
- Available commands
- Temperature Setpoint · Fan Speed · Air Direction · Drive On/Off
- Compatible models
- MelcoBEMS Mini (A1M)
- Last updated
Registers (6)
6 read, 5 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| Room Temperature | °C | Read and write | |||
| Drive Mode | Read | ||||
| Temperature Setpoint | °C | Read and write | |||
| Fan Speed | Read and write | ||||
| Air Direction | Read and write | ||||
| Drive On_Off | Read and write |
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Use cases
- Monitor room temperature and setpoint on a live cloud dashboard for each Mitsubishi indoor unit.
- Adjust temperature setpoints remotely to reduce energy consumption outside of occupied hours.
- Create an alert when room temperature deviates from the setpoint by more than 2 degrees for over 15 minutes.
- Log fan speed and air direction changes over time to verify scheduled HVAC profiles.
- Switch drive on or off remotely for seasonal shutdown or startup without an on-site visit.
- Compare drive mode and room temperature across multiple zones in a multi-unit installation.
Installation
Wire the RS-485 A and B terminals from your ModbusCloud Gateway to the corresponding Modbus terminals on the MelcoBEMS Mini (A1M) module.
Set the Modbus slave address on the A1M module using its DIP switches or configuration menu, and note the address for use in the template.
Confirm that the baud rate on the A1M is set to 9600, matching the default for this template.
Import the Mitsubishi MelcoBEMS Mini (A1M) template in the ModbusCloud platform and assign the correct slave address.
Verify communication by checking that room temperature and drive status values appear on the cloud dashboard.
If controlling multiple indoor units, repeat the wiring and address assignment for each A1M module and add each as a separate device in ModbusCloud.
Things to watch for
Why do room temperature and drive mode appear to come from the same register?
Both parameters are mapped to register address 0 on the A1M. The template handles this by reading the same address and interpreting the value according to the parameter context. No manual adjustment is needed.
What baud rate and serial settings should I use?
The default is 9600 baud, 8 data bits, no parity, 1 stop bit (9600 8N1). Make sure both the gateway and the A1M module are configured identically.
Can I control multiple indoor units from one gateway?
Yes. Each indoor unit requires its own MelcoBEMS Mini (A1M) module with a unique Modbus slave address. Connect all modules on the same RS-485 bus and add each as a separate device in ModbusCloud.
Write commands do not seem to take effect. What should I check?
Verify that the A1M module is set to allow external Modbus write access. Some installations have write protection enabled by default. Also confirm the correct slave address and that no other BMS is holding write priority on the bus.
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