ONOKOM AIR HT-1-MB-B

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

1. 1Connect the ONOKOM HS-3-MB-B gateway to the Hitachi air conditioner according to the ONOKOM wiring instructions.
2. 2Wire the RS-485 A and B terminals of the HS-3-MB-B gateway to the corresponding terminals on your ModbusCloud gateway (MCG or MLP series).
3. 3Set the baud rate on the ModbusCloud gateway to 9600 to match the ONOKOM default configuration.
4. 4Assign 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.
5. 5Import the ONOKOM AIR HT-1-MB-B template in the ModbusCloud platform and assign it to the correct Modbus address.
6. 6Verify communication by checking that indoor temperature, outdoor temperature, and AC connection status readings appear on your ModbusCloud dashboard.

Things to watch for

01

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.

02

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.

03

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.

04

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.

Registers (8)

3 read / 5 write

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