OU-AC on a Fujitsu WATERSTAGE split: Outdoor unit radiator (heat sink) temperature error
Short answer
On a Fujitsu heat pump, OU-AC means: Outdoor unit radiator (heat sink) temperature error. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Outdoor unit radiator (heat sink) temperature error.
Part involved: outdoor unit PCB/refrigerant circuit.
Likely causes:
- Heat sink overheating (R32 WOYA100KLT).
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: unknown.
Manual reset: unknown.
What you can check
- Note the error number shown after pressing the Info (i) key on the Waterstage user interface. Check the heat pump breakers/isolators are on. The hydraulic unit shows error 370; the specific code is shown by LED flashes on the hydraulic interface PCB / outdoor PCB, which only an engineer should access.
What the engineer will check
- Per SHP maintenance manual 'Clear' procedure: Heat sink overheating (R32 WOYA100KLT). Access outdoor PCB (ERROR LED, press ENTER to read flash count), check connectors, sensor resistances, supply voltage (198-264 V AC 1ph), serial signal (AC 70-130 V between terminals), valves/EEV, refrigerant charge (F-gas), fan motor, compressor windings, IPM/PFC boards.
Who to ask for: Heat pump / refrigeration engineer (manufacturer-trained).
Certification: F-gas certification for refrigerant-circuit work; electrical competence (Part P/18th Edition) for PCB/wiring.
What you might notice
Sources
- AIR TO WATER Comfort series DESIGN & TECHNICAL MANUAL Split type ↗ · DA_CF002EF_07 · page DTM p.62-63 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026