ONOKOM AIR HT-1-MB-B
Controls Hitachi air conditioners via the ONOKOM HS-3-MB-B gateway over Modbus RTU.
This template connects Hitachi air conditioners via the ONOKOM AIR HT-1-MB-B and HS-3-MB-B gateway to ModbusCloud over Modbus RTU. It reads indoor and outdoor temperatures, monitors AC connection status, and provides control over operating mode, fan speed, and target temperature.
- Protocol
- Modbus RTU
- Connection
- RS485, 9600 baud
- Registers
- 8, read and write
- Brand
- Onokom
- Key readings
- Indoor air temperature · Outdoor air temperature · AC connected status
- Available commands
- Active on/off · Operating mode · Smart fan speed · Target temperature
- Compatible models
- ONOKOM AIR HT-1-MB-B · ONOKOM HS-3-MB-B
- Last updated
Registers (8)
3 read, 5 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| Indoor air temperature | °C | Read | |||
| Outdoor air temperature | °C | Read | |||
| AC connected (Status) | Read | ||||
| Active (Control) | Write | ||||
| Loxone modes (Control) | Write | ||||
| Smart fan speed | Write | ||||
| Target temperature | °C | Write | |||
| Modbus address (Service) | Write |
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Use cases
- Monitor indoor and outdoor air temperatures on a live dashboard for each Hitachi AC unit.
- Control operating mode and target temperature remotely without accessing the indoor unit.
- Create an alert when the AC connection status indicates communication loss with the Hitachi unit.
- Schedule target temperature setpoints for different times of day to optimize energy usage.
- Verify fan speed and operating mode across multiple Hitachi units in a multi-zone installation.
Installation
Connect the ONOKOM HS-3-MB-B gateway to the Hitachi air conditioner according to the ONOKOM wiring instructions.
Wire the RS-485 A and B terminals of the HS-3-MB-B gateway to the corresponding terminals on your ModbusCloud Gateway.
Set the baud rate on the ModbusCloud gateway to 9600 to match the ONOKOM default configuration.
Assign a unique Modbus slave address to each HS-3-MB-B gateway by writing the desired address to register 128, especially when multiple units share one RS-485 bus.
Import the ONOKOM AIR HT-1-MB-B template in the ModbusCloud platform and assign it to the correct Modbus address.
Verify communication by checking that indoor temperature, outdoor temperature, and AC connection status readings appear on your ModbusCloud dashboard.
Things to watch for
The gateway is not responding on the Modbus bus. What should I check?
Verify the RS-485 wiring polarity (A and B lines) and confirm the baud rate is set to 9600. Make sure the Modbus slave address configured in ModbusCloud matches the address set on the ONOKOM gateway.
How do I change the Modbus address of the ONOKOM gateway?
Write the desired slave address to holding register 128. This is necessary when you have multiple ONOKOM gateways on the same RS-485 bus to avoid address conflicts.
The outdoor temperature shows a negative or unexpected value. Is this normal?
The outdoor temperature register uses int16 format, which supports negative values. If the reading seems incorrect, check the scaling factor and ensure the Hitachi unit is reporting outdoor sensor data to the gateway.
Can I control multiple Hitachi units from one ModbusCloud gateway?
Yes. Each Hitachi unit requires its own ONOKOM HS-3-MB-B gateway with a unique Modbus address. All gateways can share a single RS-485 bus connected to one ModbusCloud gateway.
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