General Assist Technical Reference
BACnet Gateway UTY-VBGX
System requirement for VRF systems with four outdoor units
Service Bulletin VRF-0185 | Issued 24 August 2026
Important limitation: The UTY-VBGX hardware BACnet Gateway cannot register the fourth outdoor unit (Subordinate 3) when a refrigerant circuit contains four outdoor units. In this configuration, connection to a Building Management System (BMS) is not possible.
1. Quick answer
| Affected BACnet Gateway | UTY-VBGX (Hardware) |
| Affected configuration | One refrigerant circuit containing four outdoor units |
| What happens | The fourth outdoor unit, Subordinate 3, cannot be registered in the refrigerant circuit. |
| BMS connection | Not possible for the affected four-outdoor-unit refrigerant circuit using UTY-VBGX. |
| Alternative | Consider UTY-ABGXZ1 (Software) BACnet Gateway. |
2. Affected systems
This limitation applies when the UTY-VBGX hardware BACnet Gateway is being used with a VRF refrigerant circuit that has four outdoor units.
Series identified in the bulletin as supporting a four-outdoor-unit configuration:
- VC-V Series
- V-V Series
| Outdoor unit position | Registration with UTY-VBGX |
|---|---|
| Primary | Registered |
| Subordinate 1 | Registered |
| Subordinate 2 | Registered |
| Subordinate 3 (4th outdoor unit) | Cannot be registered |
Because the fourth outdoor unit cannot be registered, the affected refrigerant circuit cannot be connected to the BMS through the UTY-VBGX hardware gateway.
3. Workaround
If a VRF refrigerant circuit with four outdoor units must be connected to BACnet, consider using the UTY-ABGXZ1 software BACnet Gateway as the alternative model.
The service bulletin does not provide a hardware modification, setting change or commissioning procedure that will make the fourth outdoor unit register with the UTY-VBGX.
4. Check before specifying or commissioning
| 1 | Confirm the BACnet Gateway model being used. |
| 2 | Confirm how many outdoor units are connected within each refrigerant circuit. |
| 3 | If the circuit has four outdoor units and UTY-VBGX is proposed, do not proceed on the assumption that the fourth outdoor unit can be registered. |
| 4 | Where BACnet/BMS connection is required for that circuit, consider UTY-ABGXZ1 (Software) instead. |
5. Future update
GENERAL is investigating the issue. If a solution is confirmed for the affected UTY-VBGX hardware BACnet Gateway, an updated response plan, including any permanent solution, will be provided.
Source: Service Bulletin VRF-0185 — System Requirements for Using BACnet Gateway, issued 24 August 2026.
BACnet® is a registered trademark of ASHRAE.
BACnet® is a registered trademark of ASHRAE.