GENERAL Assist Technical Reference
UTZ-GXXA External Power Supply Unit
VRF multi-tenant power isolation, wiring and commissioning guide
Used where individual indoor-unit mains supplies may be switched off while the remainder of the VRF system must continue operating.
What the UTZ-GXXA does: When an indoor unit loses its normal mains supply, the UTZ-GXXA provides auxiliary power to the indoor unit PCB so that communication and electronic expansion valve operation can be maintained. This prevents the powered-down indoor unit from causing communication errors or affecting other indoor units on the same refrigerant system.
Authorised service personnel only. Installation requires work on 220/230/240 V AC circuits and a 24 V AC auxiliary supply. Isolate all supplies before installation and complete electrical work in accordance with the installation manual and applicable electrical regulations.
1. When is the UTZ-GXXA used?
In a normal VRF system, switching off the mains supply to an indoor unit can stop its PCB and electronic expansion valve circuitry. Because that indoor unit remains part of the VRF communication network, this can cause a communication error and can affect operation of other indoor units connected to the same refrigerant system.
The UTZ-GXXA External Power Supply Unit is intended for applications where individual indoor units may be electrically isolated independently, such as multi-tenant buildings, but the overall VRF network must continue to operate.
| Condition | Without UTZ-GXXA | With UTZ-GXXA |
|---|---|---|
| Indoor unit mains ON | Indoor unit operates normally. | Indoor unit operates normally from its standard supply. |
| Indoor unit mains OFF | PCB/EEV power can be lost, resulting in communication error and system disruption. | Auxiliary supply maintains the required PCB/EEV and communication functions. |
Important: The UTZ-GXXA does not make a powered-down indoor unit available for normal heating or cooling operation. Its purpose is to keep the required electronics alive so the rest of the VRF system can continue without a system error.
2. UTZ-GXXA specifications
| Model | UTZ-GXXA |
| Power supply | Single-phase AC 24 V, 50/60 Hz |
| Maximum power consumption | 21 W |
| Operating temperature | 0 to 46°C |
| Dimensions | 65 × 203 × 178 mm (installation manual) |
| Weight | 500 g |
| Supplied connecting cable | 5 m |
Locally supplied electrical components
| Item | Requirement |
|---|---|
| Relay | Primary side 220-240 V AC; secondary-side rated current 3 A or more; normally closed contact; compliant with IEC 61810-1 or 60335-1. |
| Transformer | 24 V AC ±15%, UL Class II or equivalent insulation structure. |
3. Wiring arrangement
The wiring concept uses a dedicated supply that remains available even when the indoor unit's normal mains circuit is switched off.
| Step | Connection |
|---|---|
| 1 | Connect the UTZ-GXXA to the indoor unit PCB using the supplied connecting cable. Depending on the indoor-unit model, the supplied adapter cable may also be required. |
| 2 | Supply 24 V AC to the UTZ-GXXA from the dedicated transformer. The installation manual specifies 24 V AC ±20% at the unit terminal. |
| 3 | Connect the relay's normally closed contact to the UTZ-GXXA. The relay is used to detect loss of the indoor unit's normal mains supply. |
| 4 | Connect the indoor-unit power line and relay power line to the indoor-unit circuit breaker. |
| 5 | Connect the primary side of the 24 V transformer to a dedicated 220/230/240 V AC supply that is not switched off with the indoor unit. |
Multiple UTZ-GXXA units: If one transformer supplies more than one external power supply unit, confirm that the total connected load does not exceed the transformer's capacity.
4. Installation requirements
- Install within reach of the supplied 5 m connecting cable.
- Install in a well-ventilated location protected from rain and direct sunlight.
- Do not install where water can enter the enclosure via the cable entry.
- Do not install close to heat, steam, flammable gas, oil mist, corrosive gases or strong electromagnetic interference.
- Keep the power supply cable and the indoor-unit connecting cable separate; do not bind them together.
- Install the unit and wiring at least 1 m from television or radio equipment where practicable to reduce interference.
- Secure the enclosure with the four supplied tapping screws and ensure cable strain is not transferred to the terminals.
Indoor-unit connection differences
For AUXM, AUXK, AUXS, AG*A and AG*E indoor units, the supplied adapter cable is used between the UTZ-GXXA connecting cable and the indoor-unit connection. The manual also specifies fitting the supplied EMI core at the indoor-unit side where required.
For AB*A012/014/018/024 indoor units, the supplied EMI core is specifically required on the indoor-unit side of the connecting cable.
5. Commissioning and operation check
- Recheck all wiring before energising.
- Turn on the UTZ-GXXA supply and the indoor-unit supply.
- Confirm the green LED on the indoor-unit PCB is illuminated.
- Turn off the normal mains supply to the indoor unit.
- Confirm the green indoor-unit PCB LED changes to the specified blinking pattern: 3 seconds ON / 1 second OFF.
- Confirm the remainder of the VRF system continues operating without a communication error.
- Restore normal indoor-unit power and confirm normal operation.
Expected behaviour: When the indoor unit's main breaker is OFF, the UTZ-GXXA maintains the required low-voltage PCB functions. The indoor unit itself remains treated as an operation-off unit while the remainder of the system can continue operating.
6. Electricity charge apportionment
Multi-tenant billing consideration: An indoor unit whose normal power is OFF but whose PCB is being maintained by the UTZ-GXXA is handled in the same manner as an operation-off indoor unit by the electricity charge apportionment function. Because standby power may still be consumed, the calculated electricity charge for that indoor unit may not be zero.
7. Quick troubleshooting
| Symptom | Check |
|---|---|
| Communication error occurs when tenant breaker is switched OFF | Confirm 24 V AC auxiliary supply remains present; verify relay uses a normally closed contact; verify UTZ-GXXA-to-indoor-PCB connection. |
| Indoor PCB LED goes completely out when mains is switched OFF | Check transformer output, auxiliary circuit breaker, relay wiring, UTZ-GXXA input and supplied connecting cable. |
| Unit does not return to normal operation after mains is restored | Recheck all connections, confirm correct mains voltage at indoor unit, and confirm the indoor PCB green LED returns to normal indication. |
Reference: UTZ-GXXA External Power Supply Unit Installation Manual (Part No. 9384017000) and Fujitsu General control-system optional-parts documentation. Always refer to the current indoor-unit installation manual for the exact PCB connector location and model-specific requirements.