Applies To
Double skin packaged rooftop package units using the Danfoss MCX controller platform.
Reference variable list:
UNICO_v1.05.00_rev01_FG-000022-ID10.mcxs
This variable list is for the double skin rooftop package unit project reference FG-000022 and shows Modbus-related parameters, status variables, alarms and I/O addresses.
Purpose
This article provides a practical guide for service, controls and BMS integration teams when using the Modbus variable list for double skin rooftop package units.
It explains:
- How the variable list is structured
- Which addresses are commonly required for BMS integration
- Which values are read-only and which are read/write
- Key unit status, setpoint, alarm and I/O points
- Information to collect before escalating a Modbus or BMS issue
Important Notes
The attached Modbus variable list contains factory-level parameters and status variables. Do not change writable parameters unless the adjustment has been approved by Fujitsu General technical support or the equipment supplier.
Incorrect Modbus writes may affect unit operation, safety logic, compressor staging, fan control, defrost operation, setpoints or alarm behaviour.
Variable List Structure
The table is arranged with the following columns:
| Column | Meaning |
|---|---|
| LABEL | Short variable code used by the controller |
| DESCRIPTION | Description of the parameter, status or alarm |
| MIN / MAX | Permitted operating range |
| VALUE/TYPE | Default value or enum type |
| UNIT | Engineering unit, where applicable |
| RW | Read/write status |
| ADU | Modbus address/register reference |
The list includes both writable configuration parameters and read-only live values. Writable items are marked RW, while live status, alarms and I/O feedback are generally marked Read.
Modbus Communication Settings
The Modbus communication settings are located under General > Serial Settings.
| Label | Description | Default / Value | ADU |
|---|---|---|---|
| SEr | Serial address, Modbus | 10 | 7311 |
| bAU | Serial baud rate, Modbus | 19200 | 7312 |
| COM | Serial format, Modbus | 8N1 | 7313 |
The external Modbus gateway settings are listed under General > Modbus Gateway.
| Label | Description | Default / Value | ADU |
|---|---|---|---|
| XC0 | External communication enable | Auto | 7314 |
| XC1 | External communication baud rate | 19200 | 7315 |
| XC2 | External communication settings | 8N1 | 7316 |
For BMS integration, confirm the controller serial address, baud rate and serial format match the BMS configuration.
Common Writable Control Points
The following points are commonly used for BMS enable/disable, setpoint and mode control.
| Label | Description | Range | Unit | Access | ADU |
|---|---|---|---|---|---|
| y01 | System ON/OFF | 0–1 | Enum | RW | 8398 |
| y03 | System heat/cool | 0–1 | Enum | RW | 8400 |
| SC1 | Cooling temperature setpoint | SCL–SCH | °C | RW | 8261 |
| SH1 | Heating temperature setpoint | SHL–SHH | °C | RW | 8264 |
| SPr | Remote setpoint enable | 0–1 | Enum | RW | 7094 |
| Er1 | Maximum power in demand limit | 0–100 | % | RW | 7095 |
The variable list shows y01 as the System ON/OFF command, y03 as the System heat/cool command, and SC1/SH1 as the cooling and heating temperature setpoints.
Setpoint Limits
The setpoint limits define the allowable range for cooling and heating setpoints.
| Label | Description | Default | Unit | ADU |
|---|---|---|---|---|
| SCL | Minimum setpoint limit in cooling | 15.0 | °C | 7081 |
| SCH | Maximum setpoint limit in cooling | 30.0 | °C | 7082 |
| SHL | Minimum setpoint limit in heating | 15.0 | °C | 7084 |
| SHH | Maximum setpoint limit in heating | 40.0 | °C | 7085 |
If the BMS cannot write a setpoint, confirm the requested value is within the configured minimum and maximum limits.
Key Read-Only Unit Status Points
The main unit overview is located under Status var > Chiller Overview.
| Label | Description | Unit / Type | Access | ADU |
|---|---|---|---|---|
| A01 | Alarm notification | Enum | Read | 16387 |
| A02 | On/Off status | Enum | Read | 16388 |
| A03 | Compressor status | Enum | Read | 16389 |
| A10 | Remote ON/OFF | Enum | Read | 16398 |
| A11 | Defrost status | Enum | Read | 16399 |
| A12 | Cool/Heat mode | Enum | Read | 16400 |
| A13 | Control probe | °C | Read | 16480 |
| A14 | Actual setpoint | °C | Read | 16481 |
| A15 | Requested power | % | Read | 16484 |
| A16 | Actual power | % | Read | 16485 |
These are the preferred points for basic BMS monitoring of unit state, operating mode, demand and actual output.
Compressor Monitoring
The variable list provides individual compressor status, run hours and start counters.
Compressor Status
| Label | Description | Access | ADU |
|---|---|---|---|
| c01 | Compressor 1 Circuit 1 status | Read | 16417 |
| c02 | Compressor 2 Circuit 1 status | Read | 16418 |
| c03 | Compressor 3 Circuit 1 status | Read | 16419 |
| c07 | Compressor 1 Circuit 2 status | Read | 16423 |
| c08 | Compressor 2 Circuit 2 status | Read | 16424 |
The attached rooftop package unit configuration includes compressor variables for up to six compressors per circuit; however, not every compressor variable will apply to every unit size or configuration.
Compressor Run Hours
| Label | Description | Unit | Access | ADU |
|---|---|---|---|---|
| c0a | Compressor 1 Circuit 1 hours | h | Read | 16801 |
| c0b | Compressor 2 Circuit 1 hours | h | Read | 16803 |
| c0c | Compressor 3 Circuit 1 hours | h | Read | 16805 |
Run hours are useful for service planning, compressor rotation checks and fault investigation.
Rooftop Status Variables
The rooftop-specific status points are listed under Status var > Rooftop.
| Label | Description | Unit / Type | Access | ADU |
|---|---|---|---|---|
| RS00 | Supply damper on/off | Enum | Read | 17001 |
| RS01 | Supply fan on/off | Enum | Read | 17002 |
| RS02 | Supply fan speed | % | Read | 17003 |
| RS03 | External damper on/off | Enum | Read | 17004 |
| RS04 | External damper position | % | Read | 17005 |
| RS05 | Return fan on/off | Enum | Read | 17006 |
| RS06 | Return fan speed | % | Read | 17007 |
| R023 | Free cooling demand | % | Read | 17024 |
| R024 | Free heating demand | % | Read | 17025 |
| R026 | Air quality demand | % | Read | 17027 |
For rooftop package units, these are useful BMS points for confirming fan demand, damper status and economiser/free-cooling activity.
Supply Fan Parameters
Supply fan setup parameters are located under Supply Fan > Setup.
| Label | Description | Default | Unit | Access | ADU |
|---|---|---|---|---|---|
| SF0 | Regulation type | FIX | Enum | RW | 7317 |
| SF1 | Minimum speed | 10.0 | % | RW | 7318 |
| SF2 | Maximum speed | 75.0 | % | RW | 7319 |
| SF3 | Time at maximum speed at startup | 0 | s | RW | 7320 |
| SF6 | Enable supply damper | TIME | Enum | RW | 7323 |
| SF7 | Fan delay after damper | 60 | s | RW | 7324 |
| SF8 | Fan delay at OFF | 60 | sec | RW | 7325 |
The variable list confirms SF2 Maximum speed is set to 75% by default, matching the fan speed note shown in the wiring information.
External Damper / Economiser Parameters
External damper control is listed under External Damper > Configuration and related free-cooling/free-heating sections.
| Label | Description | Default | Unit | ADU |
|---|---|---|---|---|
| dE0 | Enable FreeCoolHeating | NO | Enum | 7346 |
| dE1 | Minimum opening | 20.0 | % | 7347 |
| dE2 | Maximum opening | 100.0 | % | 7528 |
| sC0 | Summer free-cooling enable | YES | Enum | 7350 |
| wH0 | Winter free-heating enable | YES | Enum | 7355 |
| wC0 | Winter free-cooling enable | YES | Enum | 7365 |
These points may only be relevant where the unit is fitted with the applicable damper, economiser or air quality options.
Alarm Monitoring
Alarms are shown in the ALARMS section. The alarm list includes the label, description, reset type, whether the alarm is active when the unit is off, and the associated Modbus ADU and bit reference.
Common Alarm Registers
| Alarm Type | Examples | ADU |
|---|---|---|
| General / phase / high pressure / low pressure alarms | A01, A02, AH1, AL1 | 20481–20482 |
| Compressor protection alarms | AC1, C01, C02, C03 | 20482–20483 |
| Fan protection alarms | A60, A61, AF1, AF2 | 20483–20484 |
| Probe and sensor alarms | P05, P14, P21, P23, P24 | 20485–20486 |
| Network and communication alarms | N01, N02, N03–N10 | 20488–20489 |
| Rooftop-specific alarms | SFA, RFA, SFL, FIR, SFW | 20491–20492 |
The alarm table indicates that alarms are mapped as individual bits within ADU registers, such as 20481 .08, 20482 .11, and similar. This means the BMS may need to read the register and decode the relevant bit, depending on the integration platform.
Common Rooftop-Specific Alarms
| Label | Description | Reset | ADU / Bit |
|---|---|---|---|
| SFA | Supply fan alarm | Manual | 20491 .06 |
| RFA | Return fan alarm | Manual | 20491 .07 |
| SFS | Supply fan safety switch | Auto | 20492 .12 |
| FIR | Fire/smoke alarm | Manual | 20492 .13 |
| SFW | Supply flow | 3 | 20492 .14 |
| SFL | Supply filter | Auto | 20492 .15 |
| FR1 | Frost alarm Circuit 1 | Auto | 20492 .00 |
| FR2 | Frost alarm Circuit 2 | Auto | 20492 .01 |
These are key points for service diagnostics where the complaint relates to airflow, filter pressure, fire trip, fan failure or frost protection.
I/O Configuration
The last pages of the variable list show physical I/O mappings.
Analogue Inputs
| Input | Description | Signal Type | Unit | ADU |
|---|---|---|---|---|
| AI1 | Return temperature | NTC-10K | °C | 21804 |
| AI2 | Outdoor temperature | NTC-10K | °C | 21768 |
| AI3 | Suction pressure Circuit 1 | 4–20 mA | barg | 21775 |
| AI5 | Discharge pressure Circuit 1 | 4–20 mA | barg | 21766 |
| AI12 | Variable setpoint | 0–10 V | — | 21769 |
| AI16 | Supply temperature | NTC-10K | °C | 21803 |
Digital Inputs
| Input | Description | Contact Type | ADU |
|---|---|---|---|
| DI1 | Remote ON/OFF | N.C. | 21309 |
| DI3 | High pressure switch Circuit 1 | N.C. | 21299 |
| DI7 | Protection Compressor 1 Circuit 1 | N.C. | 21253 |
| DI8 | Protection Compressor 2 Circuit 1 | N.C. | 21254 |
| DI11 | Protection Compressor 3 Circuit 1 | N.C. | 21255 |
| DI15 | Supply filter | N.C. | 21335 |
| DI17 | Phases/voltage status | N.C. | 21311 |
| DI18 | Remote cooling/heating | N.C. | 21314 |
| DI19 | Protection fans | N.C. | 21287 |
| DI20 | Demand limit | N.O. | 21315 |
| DI21 | Supply fan alarm | N.C. | 21326 |
| DI22 | Unit second setpoint | N.O. | 21310 |
Analogue Outputs
| Output | Description | Signal | ADU |
|---|---|---|---|
| AO1 | Sink/source side regulation value 1 | 0–10 V | 22018 |
| AO3 | Supply fan | 0–10 V | 22026 |
Digital Outputs
| Output | Description | Contact Type | ADU |
|---|---|---|---|
| DO2 | Compressor 1 Circuit 1 | N.O. | 21506 |
| DO3 | Compressor 2 Circuit 1 | N.O. | 21507 |
| DO4 | Supply damper | N.O. | 21571 |
| DO6 | Compressor 3 Circuit 1 | N.O. | 21508 |
| DO10 | Four-way valve Circuit 1 | N.C. | 21536 |
| DO12 | Supply fan | N.O. | 21568 |
| DO13 | Sink/source side regulation enable 1 | N.O. | 21532 |
| DO14 | General alarm | N.O. | 21534 |
| DO20 | Operating status | N.O. | 21567 |
These I/O points are useful when cross-checking controller status against field wiring and the electrical schematic.
BMS Integration Recommendations
When integrating to BMS:
- Confirm the fitted communication option from the model code and wiring diagram.
- Confirm whether the site is using Modbus RTU or another protocol gateway.
- Confirm Modbus address, baud rate and parity settings.
- Agree which points are monitoring-only and which points are writable.
- Avoid writing to factory parameters unless approved.
- Use status variables for monitoring rather than physical I/O where possible.
- For alarms, confirm whether the BMS can decode individual bits within alarm registers.
- Validate all values on site against the controller display before handover.
Recommended Minimum BMS Point List
For most projects, the following minimum point list is recommended:
| Purpose | Recommended Variables |
|---|---|
| Unit enable/status | y01, A02, A10 |
| Mode | y03, A12 |
| Setpoint | SC1, SH1, A14 |
| Control temperature | A13 |
| Demand/output | A15, A16 |
| Alarm status | A01 plus alarm bit registers |
| Compressor status | A03, c01, c02, c03 |
| Fan status | RS01, RS02 |
| Damper status | RS00, RS03, RS04 |
| Filter/fan alarms | SFA, SFS, SFL |
| Communication settings | SEr, bAU, COM |
Troubleshooting
| Issue | Checks |
|---|---|
| BMS cannot communicate | Confirm Modbus address, baud rate, parity, wiring polarity, shield and termination |
| Values are incorrect | Confirm register type, scaling, signed/unsigned format and whether the BMS is offsetting register numbers |
| BMS cannot write ON/OFF | Confirm write access, controller mode, remote enable configuration and whether local controls are overriding BMS |
| Setpoint write rejected | Confirm setpoint is within SCL/SCH or SHL/SHH limits |
| Alarm not matching display | Confirm BMS is decoding the correct ADU and bit position |
| Fan command present but fan not running | Check RS01/RS02, supply fan alarm, supply flow alarm and physical fan enable/output |
| Unit enabled but compressors not starting | Check requested power, compressor status, active alarms, safety chain and anti-short-cycle timers |
Escalation Information to Collect
When escalating a Modbus or BMS issue, provide:
- Full model number
- Serial number
- Variable list file name and revision
- Controller software version, if available
- BMS protocol and hardware details
- Modbus address, baud rate and parity
- Register map used by the BMS contractor
- Screenshot/export of BMS point configuration
- Photos of communication wiring and controller terminals
- Active alarm list from the controller display
- Values read from key points such as A02, A12, A13, A14, A15, A16 and A01