The IntesisBOX FJ-RC-MBS-1 (order code INMBSFGL001R000, legacy FJ-RC-MBS-1) is a Modbus gateway by Intesis (HMS Networks) that interfaces Fujitsu RAC and VRF air conditioning systems with Modbus RTU (EIA-485) networks. Unlike the sibling FJ-AC-MBS-1 — which connects to the indoor unit’s CN connector — the FJ-RC-MBS-1 attaches to the Fujitsu BWR/RWB three-wire remote-controller bus (the same bus used by the wired Fujitsu room controller). This makes it suitable for both residential RAC and commercial VRF installations.
TapHome connects to the gateway via Modbus TCP through a TCP-to-RTU bridge — the gateway itself is a native Modbus RTU slave. The template provides ON/OFF control, operating mode selection, fan speed adjustment, vane position control, thermostat with setpoint and current temperature, and error code monitoring.
Hardware connection
The gateway has two terminal blocks:
- BWR/RWB bus (3-pole plug-in terminal: B / W / R) — connects to the Fujitsu remote-controller bus. The same bus that wires a Fujitsu wired remote controller to the indoor unit. The cable is not polarity-sensitive but the colour coding (Red = Power, White = Data, Black = GND) must be respected end-to-end.
- EIA-485 bus (2-pole plug-in terminal: A+ / B-) — connects to the Modbus RTU bus where TapHome’s TCP-to-RTU bridge sits as Modbus master.
The gateway is powered directly from the AC indoor unit via the BWR bus (12 VDC) — no external power supply is needed. The AC indoor unit must therefore be connected to mains for the gateway to communicate.
Wiring diagram
There are two valid topologies on the BWR bus, selected by DIP switch SW1-P1:
- Wired remote controller present — connect the gateway in parallel with the existing Fujitsu wired controller. The controller stays Master, the gateway is configured as Slave (SW1-P1 = ON). Both the controller and Modbus can issue commands simultaneously.
- No remote controller — connect the gateway directly to the indoor unit’s BWR bus and configure it as Master (SW1-P1 = OFF, default). Only the gateway controls the AC.
Disconnect the AC unit from mains power before opening the indoor unit. Only one device on the BWR bus can be Master — if both the wired controller and the gateway are configured as Master, communication will shut down. Keep the BWR cable as far as possible from electrical wires and the ground wire; do not bundle them together. Maximum BWR bus length is 500 m / 1,640 ft, EIA-485 bus length is 1,200 m / 3,937 ft.
EIA-485 bus termination
A 120 Ω termination resistor is required at each end of the EIA-485 bus. The gateway has a built-in 120 Ω resistor that can be activated via DIP switch SW4-P4. Enable it only if the gateway sits at one end of the bus. Loop and star topologies are not allowed on EIA-485. A fail-safe biasing mechanism is required and must be supplied by the Modbus master (typically built into the TCP-to-RTU bridge).
Enabling Modbus communication
The gateway has three DIP switch banks on the front face: SW1 (Master/Slave + AC unit type), SW3 (slave address + baud rate), SW4 (temperature format + EIA-485 termination). All defaults are usable out of the box, so on a typical installation only the slave address and EIA-485 termination need to be reviewed. Every DIP switch change requires a power cycle to take effect.
SW1 — Master/Slave and machine type
| Position | Default | Function |
|---|---|---|
| SW1-P1 | OFF (Master) | OFF = gateway is BWR Master (no Fujitsu wired controller present). ON = gateway is Slave (Fujitsu wired controller is Master). |
| SW1-P2 | OFF | Reserved — keep OFF. |
| SW1-P3 | OFF (Type B) | OFF = RAC inverter G series + VRF J-II / V-II / VR-II. ON = RAC inverter / non-inverter + VRF V / S / J. Selects the active error-code table on register H:11. |
| SW1-P4 | OFF | Reserved — keep OFF. |
G series Fujitsu units have a “G” just before the power number in the model name, e.g.
ASYG09LTCA. Devices with firmware ≤ 2.1 connected to RAC G / VRF J-II / V-II / VR-II machines need to add 100 to the displayed error code before looking it up in the Intesis error table.
SW3 — Modbus slave address (P1..P6) and baud rate (P7..P8)
The slave address is binary-encoded across SW3-P1..P6 with P1 = LSB. Range: 0..63. Common examples:
| Address | P1 | P2 | P3 | P4 | P5 | P6 |
|---|---|---|---|---|---|---|
| 1 (default) | ON | OFF | OFF | OFF | OFF | OFF |
| 2 | OFF | ON | OFF | OFF | OFF | OFF |
| 3 | ON | ON | OFF | OFF | OFF | OFF |
| 10 | OFF | ON | OFF | ON | OFF | OFF |
| 63 (max) | ON | ON | ON | ON | ON | ON |
Baud rate is selected by SW3-P7, SW3-P8 and SW4-P3 combined:
| SW3-P7 | SW3-P8 | SW4-P3 | Baud rate |
|---|---|---|---|
| OFF | OFF | OFF | 2400 bps |
| ON | OFF | OFF | 4800 bps |
| OFF | ON | OFF | 9600 bps (default) |
| ON | ON | OFF | 19200 bps |
| OFF | OFF | ON | 38400 bps |
| ON | OFF | ON | 57600 bps |
| OFF | ON | ON | 76800 bps |
| ON | ON | ON | 115200 bps |
Default frame format is 8N2 (8 data bits, no parity, 2 stop bits). 8N1 is also auto-detected — no manual setting needed.
SW4 — Temperature format and EIA-485 termination
| Position | Default | Function |
|---|---|---|
| SW4-P1 | OFF (x1) | OFF = temperature in degrees x1 (e.g. 22 = 22 °C). ON = decicelsius x10 (e.g. 220 = 22.0 °C). |
| SW4-P2 | OFF (Celsius) | OFF = Celsius. ON = Fahrenheit. Cannot be combined with x10. |
| SW4-P3 | — | See SW3 baud rate table above. |
| SW4-P4 | OFF | OFF = no on-board EIA-485 termination. ON = internal 120 Ω termination connected. |
Importing the template in TapHome
Since the gateway communicates over Modbus RTU, a Modbus TCP-to-RTU bridge is required between TapHome Core and the EIA-485 bus. TapHome connects to the bridge over the local network using Modbus TCP. When importing the template, provide:
- IP Address — the bridge’s IP on the local network (default: 192.168.0.1)
- Slave ID — the gateway’s Modbus address set via SW3-P1..P6 (default: 1)
Assign a static IP address to the TCP-to-RTU bridge in the router’s DHCP settings to prevent the address from changing after a power cycle. If the bridge supports multiple slave addresses on the same EIA-485 line, you can chain up to 63 FJ-RC-MBS-1 gateways on a single bus.
Device capabilities
The template exposes 6 devices polled from holding registers H:0 through H:11.
ON/OFF
Simple switch to turn the AC unit on or off. Reads and writes register H:0 (Bool). Poll interval: 2.5 s.
Mode
Operating mode selector with the 5 modes documented by Intesis:
| Value | Mode |
|---|---|
| 0 | Auto |
| 1 | Heat |
| 2 | Dry |
| 3 | Fan |
| 4 | Cool |
The template defines 10 positions (values 0–9). Values 5–9 are placeholder slots that are not documented in the user manual and will not be reachable on real Fujitsu units. Reads and writes register H:1 (Int16). Poll interval: 2.5 s.
Fan Speed
Fan speed selector. Over the Fujitsu BWR bus only Auto, Low, Mid, High are documented:
| Value | Speed |
|---|---|
| 0 | Auto |
| 1 | Low |
| 2 | Mid |
| 3 | High |
The template defines 10 positions (values 0–9) including non-standard names like Position-5, Turbo, Position-6 and Position-7 — most of these will not be reachable on Fujitsu RAC/VRF indoor units. Register H:21 (read-only, not exposed in the template) reports the maximum number of fan speeds the connected unit actually supports. Reads and writes register H:2 (Int16). Poll interval: 2.5 s.
Vane Position
Vertical (U/D) vane position control. The user manual documents:
| Manual value | Position |
|---|---|
| 0 | Auto |
| 1 | Position 1 (Horizontal) |
| 2 | Position 2 (Horizontal) |
| 3 | Position 3 (Medium) |
| 4 | Position 4 (Vertical) |
| 5 | Position 5 (Vertical) |
| 10 | Swing |
The user manual reserves register value
10for Swing, but the TapHome template remaps Swing onto value5to keep the multi-value switch range contiguous. The template also adds non-standard slots (Position 6, Position 7, Swirl) that are not documented for Fujitsu RAC/VRF over the BWR bus — most will have no effect on real indoor units. The user-facing value labels instrings.yamlcorrect two typos present in the underlying XML (“Poistion-5 (Vetical)” → “Position 5 (Vertical)”).
Reads and writes register H:3 (Int16). Poll interval: 2.5 s.
Thermostat
Temperature setpoint (register H:4, read/write) and current reference temperature (register H:5, read-only). The setpoint range on Fujitsu units is 16–30 °C. The reference temperature shows the AC unit’s own sensor reading (or 0x8000 when no value has yet been received from the BWR bus).
The TapHome template applies a /100 divisor to the temperature registers, but the FJ-RC-MBS-1 user manual only documents two temperature modes selectable via SW4-P1: x1 (default, integer °C) and x10 (decicelsius). There is no documented x100 (centi-degree) mode for this gateway. The TapHome integration assumes the gateway is configured per the device default — values can be tuned in template scripts if scaling differs in your installation. If you observe setpoints reported as ~0.22 °C instead of 22 °C, verify the raw register values with the TapHome Modbus debug tool and adjust either the gateway’s DIP switches or the template scaling accordingly.
Poll interval: 2.5 s.
Error Code
Read-only numeric value from register H:11. Key values:
| Value | Meaning |
|---|---|
| 0 | No error |
| 65535 | Communication error between the Intesis gateway and the AC unit |
| Other | Fujitsu fault code — the active table depends on SW1-P3 (machine type) |
The full error code mapping is published in the user manual (sections 7.2 and 7.3) — RAC and VRF J-II/V-II/VR-II series share one table; VRF V/S/J series use a separate table. Codes cover indoor unit, outdoor unit, sensor, compressor, inverter and communication faults. Devices with firmware ≤ 2.1 connected to RAC G / VRF J-II / V-II / VR-II machines need to add 100 to the displayed code before looking it up.
Poll interval: 15 s.
Troubleshooting
No Modbus communication
- Verify the AC indoor unit is powered on — the gateway requires 12 VDC supplied via the BWR bus.
- Check the LED indicators: L1 + L2 pulse (5 s ON) at startup; L1 flashing (100 ms ON / 1900 ms OFF) indicates normal operation; L1 blinking (500 ms ON / 500 ms OFF) indicates a communication error with the AC unit.
- Confirm the slave address in TapHome matches the SW3-P1..P6 binary setting on the gateway.
- Ensure the TCP-to-RTU bridge is on the same network as TapHome Core and the bridge’s serial settings match SW3 baud rate (default 9600 bps, 8N2).
- Verify the EIA-485 polarity — A+ / B- must be consistent across all devices on the bus.
- Check that 120 Ω termination is enabled at both ends of the EIA-485 bus (one end is typically the bridge, the other is the gateway via SW4-P4 = ON).
Error code 65535 continuously
This indicates the gateway cannot communicate with the Fujitsu AC indoor unit over the BWR/RWB bus. Check:
- BWR cable is connected with the correct R-W-B colour order at both ends.
- The AC indoor unit is powered (mains).
- If a Fujitsu wired remote controller is also present, confirm only one device (gateway or controller) is configured as Master — verify SW1-P1 against the topology.
- BWR bus length does not exceed 500 m.
Master/Slave conflict on the BWR bus
If the wired Fujitsu remote controller and the gateway are both configured as Master, the BWR bus will collide and one or both devices will stop responding. Set SW1-P1 to ON (gateway as Slave) whenever a wired Fujitsu controller is present on the same bus, and to OFF (gateway as Master) only when no Fujitsu wired controller is connected.
Temperature values are incorrect
The template uses a /100 divisor on registers H:4 and H:5. The default DIP setting (SW4-P1 = OFF) sends temperature in integer degrees (x1) — with /100 scaling on the TapHome side, a setpoint of 22 °C will be reported as 0.22 °C. Use the Modbus debug tool in TapHome to read raw register values and compare with the expected setpoint, then either reconfigure the gateway or adjust the divisor in the template scripts.
Wrong error codes after firmware upgrade or model change
The error-code mapping depends on SW1-P3 (machine type) and on gateway firmware version. After changing the connected AC model or upgrading the gateway firmware, re-check that SW1-P3 still matches the machine type (G series + VRF J-II/V-II/VR-II → OFF; RAC inverter / non-inverter + VRF V/S/J → ON), and that the firmware-version offset (+100 on FW ≤ 2.1) is accounted for when looking codes up in the manual.
