The IntesisBOX ME-AC-MBS-1 (order code INMBSMIT001I000, legacy ME-AC-MBS-1) is a Modbus RTU gateway by Intesis (HMS Networks) that interfaces Mitsubishi Electric air conditioners — Domestic, Mr. Slim and City Multi indoor units — with Modbus RTU (EIA-485) networks. The gateway plugs into the indoor unit’s CN105 socket via a fixed 1.5 m supplied cable and supports one indoor unit per gateway.
Unlike the sibling IntesisBOX RC variants (DK-RC-MBS-1, LG-RC-MBS-1, HS-RC-MBS-1) that tap into a wired remote-controller bus, the ME-AC-MBS-1 uses Mitsubishi’s dedicated CN105 5 V control connector on the indoor unit’s electronic control board. The gateway is bus-powered from CN105 (12 VDC, 0.72 W) — no external power supply is needed. The Mitsubishi indoor unit must therefore be connected to mains for the gateway to communicate.
TapHome connects to the gateway via a Modbus TCP-to-RTU bridge — the gateway itself is a native Modbus RTU slave with no built-in Ethernet. 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. Per-model compatibility for specific Mitsubishi indoor units can be verified using the Intesis compatibility tool.
Hardware connection
The gateway has two ports:
- AC unit port — a dedicated keyed connector for the supplied 1.5 m cable, the other end of which plugs into the CN105 socket on the Mitsubishi indoor unit’s electronic control board. Cable length is fixed; do not extend or shorten it.
- EIA-485 bus (2-pole green plug-in terminal: A / B) — connects to the Modbus RTU bus where TapHome’s TCP-to-RTU bridge sits as Modbus master. Observe polarity on this side.
System topology
Up to 63 ME-AC-MBS-1 gateways can share the same Modbus RTU EIA-485 bus, each addressed via SW3-P1..P6. Each gateway connects to one Mitsubishi indoor unit on its own CN105 connector (this is a single-IDU “AC” gateway — for multi-IDU installations, deploy one INMBSMIT001I000 per indoor unit). TapHome (acting as Modbus master through a TCP-to-RTU bridge) sees every gateway as a separate Modbus slave.
CN105 cable wiring
The CN105 connection is made with the cable shipped in the box. The shorter uncovered end plugs into the gateway’s AC-unit socket; the longer uncovered end plugs into the CN105 socket on the indoor-unit PCB. The gateway can be installed inside the indoor unit (on supported AC models) or wall-mounted next to it.
Disconnect the AC unit from mains power before opening the indoor unit. The supplied CN105 cable is 1.5 m long — do not modify its length. Extending or shortening the cable can cause communication malfunctions. Keep the cable away from electrical wires and ground wires; do not bundle them together.
Wall mount
For wall mounting next to the indoor unit, extract the upper and lower staples on the gateway housing until they click. Use the dedicated cable hole and fix the cable with the supplied staple and screw. Key dimensions shown on the installation diagram: 200 mm / 7.9" (free cable section between strain relief and CN105 connector), 40 mm / 1.6" (short cable section on the gateway side), 90 mm / 3.5" (gateway height) and 53 mm / 2.1" (gateway width). The enclosure is 93 × 53 × 58 mm and supports DIN-rail (TH35) mounting via the included bracket.
EIA-485 wiring and termination
The EIA-485 bus polarity must be respected: A to A, B to B across all devices on the bus. Maximum EIA-485 bus length is 1,200 m / 3,937 ft. Loop and star topologies are not allowed — the bus must be wired as a daisy chain.
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. A fail-safe biasing mechanism is required and must be supplied by the Modbus master (typically built into the TCP-to-RTU bridge). Up to 63 gateways can share one bus; Modbus repeaters may be required on long lines or with many slaves.
Configuration
The ME-AC-MBS-1 is configurable via on-board DIP switches and via Modbus registers. Default settings (slave address 1, 9600 bps 8N2, all other DIP switches OFF) work out of the box on a typical installation, so usually only the slave address, the temperature scale (SW4-P1 / SW4-P2) and the EIA-485 termination need to be reviewed. Every DIP-switch change requires a power cycle of the gateway to take effect — that is, disconnecting the AC indoor unit from mains so the CN105 line loses its 12 VDC supply, then reconnecting after a few seconds.
DIP-switch layout
The gateway has three DIP-switch banks: SW1 (4 positions, AC indoor-unit fan-speed and vane features), SW3 (8 positions, Modbus slave address + baud rate) and SW4 (4 positions, temperature format + EIA-485 termination).
Enabling Modbus communication
The ME-AC-MBS-1 ships with Modbus RTU communication enabled by default — there is no menu navigation or web UI to activate it. Setting up Modbus is a matter of selecting the correct slave address, baud rate and frame format on the DIP switches. The gateway implements Modbus functions 3 (Read Holding Registers), 4 (Read Input Registers), 6 (Write Single Register) and 16 (Write Multiple Registers — limited to 1 register per request).
SW1 — AC indoor-unit fan speeds and vanes
SW1 tells the gateway how many fan speeds the connected Mitsubishi unit supports and whether the vanes have an Auto position. The gateway uses this to constrain the value range of register H:21 (max number of fan speeds, read-only).
| SW1-P1 | SW1-P2 | SW1-P4 | Setting |
|---|---|---|---|
| OFF | OFF | OFF | AC indoor unit has 4 fan speeds and AUTO (default) |
| ON | OFF | OFF | AC indoor unit has 4 fan speeds (no Auto) |
| OFF | ON | OFF | AC indoor unit has 3 fan speeds and AUTO |
| ON | ON | OFF | AC indoor unit has 3 fan speeds (no Auto) |
| OFF | ON | ON | AC indoor unit has 2 fan speeds |
| SW1-P3 | Setting |
|---|---|
| ON | AC indoor unit with auto vanes (default) |
| OFF | AC indoor unit without auto vanes |
SW3 — Modbus slave address (P1..P6) and baud rate (P7..P8)
The slave address is binary-encoded across SW3-P1..P6 with P1 = LSB (P1=1, P2=2, P3=4, P4=8, P5=16, P6=32). Range: 1..63 (address 0 is reserved as Modbus broadcast). 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 scale, baud rate bit and EIA-485 termination
| Position | Default (OFF) | ON |
|---|---|---|
| SW4-P1 | Temperature in degrees ×1 (e.g. 22 = 22 °C). | Temperature in decidegrees ×10 (e.g. 220 = 22.0 °C). |
| SW4-P2 | Celsius. | Fahrenheit. Cannot be combined with ×10. |
| SW4-P3 | — | See SW3 baud rate table above. |
| SW4-P4 | No on-board EIA-485 termination. | 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 ME-AC-MBS-1 gateways on a single bus — one per Mitsubishi indoor unit.
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. The gateway and the Mitsubishi remote controllers can be used simultaneously — Modbus commands and the AC’s own remote both act on the indoor unit. Reads and writes register H:0 (Bool). Poll interval: 2.5 s.
Mode
Operating mode selector with the 5 modes documented by Mitsubishi:
| 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 Mitsubishi indoor units. The actual modes available also depend on the AC unit’s capabilities — some Mitsubishi IDUs may not support all five modes. Reads and writes register H:1 (Int16). Poll interval: 2.5 s.
Fan Speed
Fan speed selector. The Mitsubishi user manual documents the following encoding on the CN105 link:
| Manual value | Speed |
|---|---|
| 0 | Auto |
| 1 | Low |
| 2 | Mid-1 |
| 3 | Mid-2 |
| 4 | High |
The TapHome template reorders the fan-speed labels relative to the Mitsubishi register encoding. Selecting template slot 2 (labelled “Position-5”) writes register value 2 to the indoor unit, which actually corresponds to Mid-1 per the manual. Selecting template slot 3 (labelled “Mid-1”) writes register value 3 → Mid-2. Selecting template slot 5 (labelled “Mid-2”) writes register value 5 → undocumented. Effectively only Auto, Low and High are correctly labelled; Mid-1 and Mid-2 slots are misplaced and a “Position-5” label is borrowed from the sibling vane register. Verify the actual fan-speed mapping at commissioning. The number of usable speeds depends on SW1-P1..P4 (configurable for 2/3/4 speeds with or without Auto); register H:21 (read-only, not exposed in the template) reports the current maximum.
Reads and writes register H:2 (Int16). Poll interval: 2.5 s.
Vane Position
Vertical (U/D) vane position control. The Mitsubishi user manual documents only 7 valid values (0–5 plus 10 for Swing):
| Manual value | Position |
|---|---|
| 0 | Auto |
| 1 | Horizontal |
| 2 | Position-2 |
| 3 | Position-3 |
| 4 | Position-4 |
| 5 | Vertical |
| 10 | Swing |
The TapHome template remaps Mitsubishi’s sparse value set (0–5 + 10) onto the contiguous MultiValueSwitch range 0–9, with several mismatches versus the manual:
- Slot 0 “No Swing” corresponds to register value 0 — but the Mitsubishi manual defines value 0 as Auto, not “No Swing”.
- Slot 1 “Position-1” corresponds to register value 1 — but the manual defines value 1 as Horizontal.
- Slot 5 “Swing” writes register value 5 — but the manual reserves value 5 for Vertical, with Swing on value 10. Selecting “Swing” in TapHome will set the vane to Vertical on a real Mitsubishi unit, not Swing. The Vertical position is missing from the template entirely.
- Slots 6–9 (“Position-4 (Vertical)”, “Position-6”, “Poistion-7” — note the typo, “Swirl”) write values 6–9, which are entirely undocumented for the Mitsubishi vane register. “Swirl” is borrowed from sibling LG gateways and has no equivalent on Mitsubishi.
Verify the actual physical vane positions at commissioning rather than relying on the labels. Available positions also depend on SW1-P3 (auto-vanes presence) and on the specific IDU model — refer to the Intesis IDU compatibility matrix.
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). Valid ranges per the Mitsubishi user manual:
- Setpoint: 16–32 °C (61–90 °F)
- Reference temperature: 10–38 °C (50–100 °F)
Both registers report −32678 at startup until the gateway has read a value from the indoor unit. The reference temperature reflects the indoor unit’s own control-loop sensor — either the return-air sensor or the remote-controller sensor, depending on the IDU configuration.
The TapHome template applies a /100 divisor to the temperature registers, but the ME-AC-MBS-1 user manual only documents three temperature modes selectable via SW4-P1 / SW4-P2: ×1 Celsius (default), ×10 decicelsius and Fahrenheit (×1). There is no documented ×100 (centi-degree) mode for this gateway. On a default-configured Celsius unit, setpoints can therefore appear 100× too small (e.g.
0.22 °Cinstead of22 °C); on a ×10 decicelsius configuration they will be 10× too small. Use the Modbus debug tool in TapHome to read raw register values and compare with the expected setpoint, then either reconfigure the gateway DIP switches or adjust the divisor in the template scripts.
Poll interval: 2.5 s.
Error Code
Read-only numeric value from register H:11. Key values:
| Value | Meaning |
|---|---|
| 0 | No active error |
| 65535 (−1 signed) | Communication error between the Intesis gateway and the AC unit |
| Other | Mitsubishi fault code — 4-digit numeric value, see the table below |
The Mitsubishi user manual documents 45 numeric error codes covering compressor, sensor, MNET line, transmission and remote-controller faults. Selected representative codes (full list in section 7 of the user manual):
| Range | Category examples |
|---|---|
| 1102–1108 | Discharge temperature high; internal thermostat detector working (49C) |
| 1110–1300 | Outdoor unit fail; pressure low |
| 1302–1520 | Pressure high (63H); freeze / overheat protection; superheating anomaly |
| 2500–2503 | Drain pump erroneous operation; drain sensor anomaly (DS) |
| 4030–4124 | Serial transmission errors; compressor overcurrent (initial / overload); phase detection / anti-phase faults |
| 4210–4230 | Compressor over-current cut; voltage anomaly; radiator panel temperature anomaly (TH8) |
| 5101–5300 | Indoor / outdoor probe anomalies (TH1, TH2, TH3, TH5–TH8); discharge temperature error; current probe error |
| 6600–6608 | MNET duplicated address; MNET hardware / bus / transmission errors |
| 6831–6846 | Remote-command and indoor↔outdoor transmission errors; inter-connection cable errors; initial timer deactivated |
| 65535 | Gateway↔AC communication failure (signed −1) |
The same numeric error code is reported on the Mitsubishi wired remote controller’s display — useful for cross-checking faults from the TapHome side without physical access to the controller. Codes in the 5xxx range typically indicate sensor / probe issues, 4xxx compressor or electrical faults, 6xxx transmission / addressing faults. The companion register H:10 (Alarm Status, read-only, not exposed in the template) is a 0/1 boolean — useful for triggering automation rules without parsing the full error-code table.
Poll interval: 15 s (vs 2.5 s for the control registers).
Troubleshooting
No Modbus communication
- Verify the Mitsubishi indoor unit is powered on — the gateway is bus-powered from CN105 (12 VDC) and will not respond at all until the indoor unit’s mains is connected.
- Check the on-board status LED:
- 5 s ON pulse on power-up — device reset / power-up.
- 200 ms ON / 2 s OFF flashing — device correctly configured and working.
- OFF continuously — no Modbus slave address configured (verify SW3-P1..P6).
- 200 ms ON / 200 ms OFF blinking — communication error between gateway and AC unit.
- Confirm the slave address in TapHome matches the SW3-P1..P6 binary setting on the gateway (each pin = one bit, P1 = LSB).
- Ensure the TCP-to-RTU bridge is on the same network as TapHome Core and the bridge’s serial settings match SW3 + SW4-P3 baud rate (default 9600 bps, 8N2 — 8N1 is auto-detected).
- 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 Mitsubishi AC indoor unit over the CN105 link. Check:
- The supplied 1.5 m cable is firmly seated in both the gateway’s AC-unit port and the indoor unit’s CN105 socket.
- The cable has not been extended, shortened or modified.
- The Mitsubishi indoor unit is powered (mains).
- The on-board status LED is blinking 200 ms / 200 ms — confirming a CN105-side comm error.
- The indoor unit model is on the Intesis compatibility list.
Temperature values are incorrect
The template uses a /100 divisor on registers H:4 and H:5. The default Mitsubishi DIP setting (SW4-P1 = OFF, SW4-P2 = OFF) sends temperature in integer degrees Celsius (×1) — 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 DIP switches or adjust the divisor in the template scripts.
Setpoint differs from the Mitsubishi remote controller display
If the Virtual Temperature mechanism has been activated by writing an external ambient reference to register H:22 (read/write, not exposed in the template), the indoor unit applies an adjusted internal setpoint following S_AC = S_u − (T_u − T_AC). While Virtual Temperature is active:
- The Mitsubishi remote controllers cannot change the setpoint — the indoor unit’s setpoint is exclusively driven by the Modbus side.
- The remote controller may display a different number than the user-requested setpoint (register H:4).
- Register H:23 (Real setpoint readback, read-only, not exposed in the template) reports the value actually applied to the indoor unit.
To deactivate the Virtual Temperature mechanism from the Modbus side, write −32768 (0x8000) to register H:22 — this clears the external reference and returns setpoint control to both Modbus and the Mitsubishi remote controllers (operating simultaneously again).
Fan Speed and Vane Position labels are wrong
The TapHome template’s MultiValueSwitch label-to-value mapping does not fully match the Mitsubishi register encoding (see the warnings under “Fan Speed” and “Vane Position” above). Until the template is corrected, choose the slot that produces the desired physical behaviour rather than relying on the label — and document the working mapping in the project notes after commissioning.
DIP-switch change has no effect
Every DIP-switch change requires a power cycle of the gateway to apply. Power cycling means disconnecting the AC indoor unit from mains (which removes the 12 VDC supply on the CN105 line) and reconnecting after a few seconds. Modifying DIP switches while the gateway is powered will not change the active configuration.
