Modbus / BMS Technical Reference
Single Skin Rooftop Units - Multipower Modbus Variable List
Controller variable list: Multipower v9.31.01
Reference: 1008180SM00 RTQ-MK single - Multipower_v9.31.01 - Level 0 End User
This article provides service, technical support, controls contractors and BMS integrators with the key Modbus points used on single skin rooftop package units for control, status monitoring, alarms and physical I/O verification.
Applies To
Single skin rooftop package units using the Multipower v9.31.01 controller variable list.
| Reference file | 1008180SM00 RTQ-MK single - Multipower_v9.31.01 - Level 0 End User |
| Application | Single circuit / single skin rooftop package unit Modbus variable list |
Purpose
The point list is intended to support:
- Unit ON/OFF control
- Cooling and heating setpoint control
- Heat/cool mode selection
- Unit status monitoring
- Compressor status and run counters
- Alarm monitoring
- Physical I/O verification
Important: The list is marked Level 0 = End User. It is a limited end-user Modbus point set, not the full factory parameter list. Only approved writable points should be adjusted.
Variable List Structure
| Column | Meaning |
|---|
| LABEL | Controller variable code |
| DESCRIPTION | Function of the variable |
| MIN / MAX | Allowable range |
| VALUE/TYPE | Default value or enumeration type |
| UNIT | Measurement unit |
| RW | Read/write access |
| ADU | Modbus register/address reference |
RW Writable by an approved controller or BMS.
Read Monitoring only. Do not write to these points.
Common Writable Control Points
| Label | Description | Range | Default / Type | Unit | Access | ADU |
|---|
| SC1 | Cooling temperature setpoint | SCL-SCH | 20.0 | °C | RW | 8261 |
| SH1 | Heating temperature setpoint | SHL-SHH | 20.0 | °C | RW | 8264 |
| y01 | System ON/OFF | 0-1 | 0 = OFF | Enum 22 | RW | 8398 |
| y03 | System heat/cool | 0-1 | 0 = COOL | Enum 36 | RW | 8400 |
| y05 | Temperature and pressure measurement unit | 0-1 | 0 = °C | Enum 13 | RW | 7031 |
Key Unit Status Points
The main unit status values are listed under Status var > Chiller Overview.
| Label | Description | Unit / Type | Access | ADU |
|---|
| A01 | Alarm notification | - | Read | 16387 |
| A02 | On/Off status | Enum 22 | Read | 16388 |
| A03 | Compressor status | Enum 51 | Read | 16389 |
| A07 | Evaporator pump | Enum 52 | Read | 16395 |
| A08 | Condenser fan/pump | Enum 52 | Read | 16396 |
| A09 | Heaters | Enum 22 | Read | 16397 |
| A10 | Remote ON/OFF | Enum 22 | Read | 16398 |
| A11 | Defrost status | Enum 22 | Read | 16399 |
| A12 | Cool/Heat mode | Enum 55 | Read | 16400 |
| A13 | Control probe | °C | Read | 16480 |
| A14 | Actual setpoint | °C | Read | 16481 |
| A15 | Requested power | % | Read | 16484 |
| A16 | Actual power | % | Read | 16485 |
Expansion Valve Monitoring
| Label | Description | Unit | Access | ADU |
|---|
| E1a | Valve opening degree | % | Read | 20738 |
| E1b | S2 temperature | °C | Read | 20741 |
| E1c | Actual superheat | °C | Read | 20742 |
| E1e | Superheat reference | °C | Read | 20743 |
| E1g | Evaporator pressure | Bar | Read | 20744 |
| E1h | Evaporator temperature | °C | Read | 20745 |
| E1n | Expansion valve status | Enum 22 | Read | 20749 |
Expansion Valve 2 points are also listed, but they may not apply to all single-circuit units. Confirm the installed configuration before adding unused points to the BMS.
Compressor Monitoring
Compressor Status
| Label | Description | Access | ADU |
|---|
| c01 | Compressor 1 Circuit 1 | Read | 16417 |
| c02 | Compressor 2 Circuit 1 | Read | 16418 |
| c03 | Compressor 3 Circuit 1 | Read | 16419 |
| c04 | Compressor 4 Circuit 1 | Read | 16420 |
| c05 | Compressor 5 Circuit 1 | Read | 16421 |
| c06 | Compressor 6 Circuit 1 | Read | 16422 |
Compressor Ageing / Hours
| Label | Description | Unit | Access | ADU |
|---|
| c0a | Compressor 1 C1 ageing | h | Read | 16801 |
| c0b | Compressor 2 C1 ageing | h | Read | 16803 |
| c0c | Compressor 3 C1 ageing | h | Read | 16805 |
| c0d | Compressor 4 C1 ageing | h | Read | 16807 |
Compressor Start Counters
| Label | Description | Access | ADU |
|---|
| G01 | Compressor 1 C1 starts | Read | 16670 |
| G02 | Compressor 2 C1 starts | Read | 16671 |
| G03 | Compressor 3 C1 starts | Read | 16672 |
| G04 | Compressor 4 C1 starts | Read | 16673 |
Alarm Register Overview
Alarm points are shown as register + bit references, for example 20481 .08, 20482 .11 and 20491 .06. The BMS may need to read the register and decode the individual bit position.
Common Alarm Points
| Label | Description | Reset | ADU / Bit |
|---|
| A01 | General alarm | Manual | 20481 .08 |
| A02 | Phase loss alarm | 3 | 20481 .09 |
| AH1 | Circuit 1 high pressure or compressor 1 protection alarm | Manual | 20481 .05 |
| AL1 | Circuit 1 low pressure alarm | ALr | 20482 .11 |
| AC1 | Circuit 1 compressor protection | Manual | 20482 .01 |
| A60 | General condenser fan protection | Auto | 20483 .15 |
| AF1 | Condenser fan 1 protection alarm | Auto | 20483 .02 |
| N01 | Network error | Auto | 20488 .04 |
| INV | Compressor inverter alarm | Manual | 20489 .02 |
| MBI | Modbus inverter communication error | Auto | 20489 .03 |
| SFA | Supply fan or phase loss alarm | Manual | 20491 .06 |
| SFL | Supply filter | Auto | 20492 .15 |
| FIR | Fire alarm | Manual | 20492 .13 |
Rooftop & Airside Alarms
| Label | Description | Reset | ADU / Bit |
|---|
| IDL | Supply damper locked | Manual | 20491 .02 |
| IDA | Supply damper alarm | Manual | 20491 .03 |
| EDL | External damper locked | Manual | 20491 .04 |
| EDA | External damper alarm | Manual | 20491 .05 |
| SFA | Supply fan or phase loss alarm | Manual | 20491 .06 |
| RFA | Return fan alarm | Manual | 20491 .07 |
| SFS | Supply fan safety switch | Auto | 20492 .12 |
| SFW | Supply flow | 3 | 20492 .14 |
| SFL | Supply filter | Auto | 20492 .15 |
I/O Configuration
Analogue Inputs
| AI | Description | Signal Type | Unit | Access | ADU |
|---|
| 1 | Discharge Pressure Circuit 1 | 4-20 mA | barg | Read | 21766 |
| 3 | RT Supply Temperature | NTC-10K | °C | Read | 21803 |
| 4 | Remote Cooling/Heating | ON/OFF | - | Read | 21798 |
| 7 | RT Return Temperature | NTC-10K | °C | Read | 21804 |
| 8 | Outdoor Temperature | NTC-10K | °C | Read | 21768 |
| - | Return Humidity | 4-20 mA | % | Read | 21809 |
| - | Outdoor Humidity | 4-20 mA | % | Read | 21810 |
Digital Inputs
| DI | Description | Contact Type | Access | ADU |
|---|
| 1 | High Pressure Switch Circuit 1 | N.C. | Read | 21299 |
| 3 | Low Pressure Switch Circuit 1 | N.C. | Read | 21302 |
| 5 | Protection Condenser Fans | N.C. | Read | 21287 |
| 6 | Supply Filter | N.C. | Read | 21335 |
| 7 | Supply Fan Alarm | N.C. | Read | 21326 |
| 8 | Remote ON/OFF | N.C. | Read | 21309 |
Analogue Outputs
| AO | Description | Signal | Unit | Access | ADU |
|---|
| 1 | Condenser speed fan 1 | 0-10 V | % | Read | 22018 |
| 3 | Supply fan | 0-10 V | % | Read | 22026 |
| 4 | External damper | 0-10 V | % | Read | 22028 |
Digital Outputs
| DO | Description | Contact Type | Access | ADU |
|---|
| 1 | Compressor 1 Circuit 1 | N.O. | Read | 21506 |
| 3 | Four-way valve Circuit 1 | N.C. | Read | 21536 |
| 5 | Condenser fan 1 | N.O. | Read | 21524 |
| 6 | Supply damper | N.O. | Read | 21571 |
| 7 | Supply fan | N.O. | Read | 21568 |
| 8 | General alarm | N.O. | Read | 21534 |
Recommended Minimum BMS Point List
| Purpose | Recommended Points |
|---|
| Unit command | y01 |
| Heat/cool command | y03 |
| Cooling setpoint | SC1 |
| Heating setpoint | SH1 |
| Unit on/off feedback | A02 |
| Alarm status | A01 |
| Compressor status | A03, c01 |
| Mode feedback | A12 |
| Control temperature | A13 |
| Actual setpoint | A14 |
| Requested output | A15 |
| Actual output | A16 |
| Remote ON/OFF feedback | A10 |
| Supply fan alarm | SFA |
| Supply filter alarm | SFL |
| Fire alarm | FIR |
| Physical supply fan output | DO7 / ADU 21568 |
| General alarm output | DO8 / ADU 21534 |
BMS Integration Guidance
- Confirm the exact unit model and whether the unit is single circuit or double circuit.
- Confirm the Modbus register format required by the BMS platform.
- Confirm whether the BMS uses zero-based or one-based register addressing.
- Confirm which alarm points require bit-level decoding.
- Only write to approved writable points such as ON/OFF, heat/cool mode and setpoints.
- Do not write to read-only status, alarm or physical I/O points.
- Validate BMS readings against the controller display during commissioning.
- Avoid adding non-applicable Circuit 2 points for single-circuit units unless required by the controls specification.
Troubleshooting
| Issue | Recommended Checks |
|---|
| BMS cannot start the unit | Check y01 command, A02 status, A10 remote ON/OFF status and active alarms |
| Unit will not change heating/cooling mode | Check y03 command, A12 feedback and remote cooling/heating input |
| Setpoint write is not accepted | Confirm the requested value is within the permitted setpoint range |
| Alarm shown on controller but not BMS | Confirm alarm register and bit decoding |
| Compressor not running | Check A03, c01, requested power A15, actual power A16 and active compressor protection alarms |
| Supply fan fault | Check SFA, SFS, SFW, DI7 and DO7 |
| Filter alarm | Check SFL and DI6 / Supply Filter input |
| Incorrect temperatures | Confirm sensor values at A13, supply temperature AI3 and return temperature AI7 |
| Communication values appear shifted | Confirm BMS register offset and address format |
Escalation Information to Collect
- Full unit model number
- Unit serial number
- Variable list file name and revision
- Confirmation that the single skin / single circuit point list is being used
- BMS protocol and hardware details
- Register list configured in the BMS
- Whether the BMS uses zero-based or one-based addressing
- Screenshots of key BMS point values
- Photos of the controller communication wiring
- Active alarms from the unit controller
- Values for A01, A02, A03, A10, A12, A13, A14, A15 and A16
Control safety: Do not write to status, alarm or physical I/O points. Incorrect writes to approved control points can also affect unit operation, setpoints and BMS sequencing. Confirm register addressing and point permissions before commissioning.
