The IntesisBOX FJ-AC-MBS-1 (order code IN485FGL001I000, legacy INMBSFGL001I000) is a Modbus gateway by Intesis (HMS Networks) that interfaces Fujitsu RAC and VRF air conditioning indoor units with Modbus RTU (EIA-485) networks. TapHome connects to the gateway via Modbus TCP using a TCP-to-RTU bridge — the gateway itself communicates with the Fujitsu AC unit over the proprietary CN65 connector.
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 connection interfaces:
- CN65 connector — connects to the Fujitsu AC indoor unit’s CN65 socket on the internal control board via a supplied 200 mm cable
- EIA-485 connector (3 poles, A+ / B- / SG) — connects to the Modbus RTU bus (max 1,200 m, no loop or star topologies)
The gateway is powered directly from the AC indoor unit (12 VDC) — no external power supply is needed. Mounting options include DIN rail (EN60715 TH35), wall mount, or inside the AC indoor unit.
Disconnect the AC unit from mains power before opening the indoor unit and connecting the gateway. The supplied cable is 200 mm long — extending or shortening it may cause malfunction. Keep the connecting cable as far as possible from electrical wires and ground wires.
EIA-485 bus termination
A 120 ohm termination resistor is required at each end of the EIA-485 bus. The gateway has a built-in 120 ohm resistor that can be activated via DIP switch SW3 position P1 (labeled SW4 P1 in the user manual). Enable it only if the gateway is at one end of the bus.
DIP switch configuration
The gateway has three DIP switch banks: SW1 (AC configuration and baud rate), SW2 (Modbus address and temperature format), and SW3 (bus polarization and termination). All changes require a power cycle.
Temperature scaling (SW2-P7/P8) — important for TapHome
The TapHome template divides temperature register values by 100. The default DIP switch setting sends temperature in degrees (x1), meaning a setpoint of 22 C is transmitted as 22 in the register. The template then divides by 100, yielding 0.22 C — which is incorrect.
The template uses a division factor of 100, but the default DIP switch setting (x1 mode) sends integer degree values. With x1, a value of 22 divided by 100 gives 0.22 C instead of the expected 22.0 C. Neither the x1 nor x10 DIP switch setting matches the template’s /100 scaling perfectly. Verify the actual register values with the Modbus debug tool in TapHome and adjust the DIP switch or template scaling as needed for your installation.
| SW2-P7 | Description |
|---|---|
| OFF | Temperature magnitude x1 (1 C = value 1) (default) |
| ON | Temperature magnitude x10 (1 C = value 10) |
| SW2-P8 | Description |
|---|---|
| OFF | Temperature in degrees Celsius (default) |
| ON | Temperature in degrees Fahrenheit |
Modbus address (SW2-P1..P6)
Binary-encoded slave address, range 1-63. Default: 1 (only P1 is ON). Positions P7 and P8 of SW2 control temperature format (see above).
Baud rate (SW1-P6..P8)
Default: 9600 bps. Available rates: 2400, 4800, 9600, 19200, 38400, 57600, 76800, 115200 bps.
| SW1-P6 | SW1-P7 | SW1-P8 | 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 |
Bus termination and polarization (SW3)
| SW3 Position | Description |
|---|---|
| P1 | EIA-485 bus 120 ohm termination — OFF: disabled (default), ON: enabled |
| P3 | EIA-485 bus polarization — OFF: disabled (default), ON: active |
TapHome connection
Since the IntesisBOX communicates via Modbus RTU (EIA-485), 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 in TapHome, provide:
- IP Address — the TCP-to-RTU bridge’s IP on the local network (default: 192.168.0.1)
- Slave ID — the gateway’s Modbus address set via DIP switches (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.
Device capabilities
The template exposes 6 devices communicating over 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 5 standard 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 not documented in the user manual and are placeholder slots — most installations will only use the first five.
Reads and writes register H:1 (Int16). Poll interval: 2.5 s.
Fan Speed
Fan speed selector. Fujitsu supports up to 4 named fan speeds plus auto:
| Value | Speed |
|---|---|
| 0 | Auto |
| 1 | Quiet |
| 2 | Low |
| 3 | Mid |
| 4 | High |
The template defines 10 positions (values 0-9). The user manual documents 5 functional positions: Auto (0), Quiet (1), Low (2), Med (3), and High (4). Register H:21 reports the maximum number of fan speeds supported by the connected unit. Values beyond the documented range will have no effect.
Reads and writes register H:2 (Int16). Poll interval: 2.5 s.
Vane Position
Vertical vane (U/D) position control. The user manual documents positions 1-4 and Swing (value 10). The template remaps these into a contiguous range for the multi-value switch:
| Value (template) | Position |
|---|---|
| 1 | Position 1 (Horizontal) |
| 2 | Position 2 (Horizontal) |
| 3 | Position 3 (Medium) |
| 4 | Position 4 (Vertical) |
| 5 | Swing |
The user manual documents Swing as value 10, but the template maps it to value 5 to create a contiguous range for the multi-value switch. Values 6-9 are positional placeholders. The number of available vane positions depends on the connected Fujitsu model.
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 template divides read values by 100 and multiplies written values by 100.
The setpoint range is 16-30 C. The reference temperature shows the AC unit’s own sensor reading unless an external sensor value has been written to register H:22.
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 gateway and AC unit |
| Other | Fujitsu error code (see user manual for full error table) |
Fujitsu error codes differ between RAC/VRF series. RAC and VRF J-II/V-II/VR-II series use codes 1-91 covering indoor unit, outdoor unit, sensor, compressor, and inverter errors. VRF V/S/J series use a separate error code range.
Poll interval: 15 s.
Troubleshooting
No Modbus communication
- Verify the AC indoor unit is powered on — the gateway requires 12 VDC from the AC unit
- Check the LED indicators: L1+L2 pulse (5 s ON) indicates startup; L1 flashing (100 ms ON, 1900 ms OFF) indicates normal operation; L1 blinking (500 ms ON, 500 ms OFF) indicates communication error with AC unit
- Confirm the slave address in TapHome matches the DIP switch SW2 setting on the gateway
- Ensure the TCP-to-RTU bridge is on the same network as TapHome Core
- Verify the EIA-485 polarity: A+ / B- must be consistent across all devices on the bus
Error code 65535 continuously
This indicates the gateway cannot communicate with the Fujitsu AC indoor unit over the CN65 connector. Check the cable between the gateway and the CN65 socket on the AC unit’s internal control board. Verify the AC unit is powered on and the connection cable is the original 200 mm cable supplied with the gateway.
Temperature values are incorrect
The template uses a division factor of 100 for temperature registers. The default DIP switch SW2 configuration sends temperature in degrees (x1). Verify DIP switch SW2 positions 7 and 8 match the expected scaling. Use the Modbus debug tool in TapHome to read raw register values and compare with the expected temperature.
