What U0 means
Daikin VRV IV-S service literature lists U0 as refrigerant shortage. Treat it as a starting point for model-specific refrigerant diagnosis, not as permission to add charge by pressure.
Likely causes and things to check
- Refrigerant leak or insufficient refrigerant mass
- Charge quantity does not match the installed piping/application
- A refrigeration or sensing condition that must be checked against the exact model service procedure
Where to start
Verify airflow/load and record the complete model and operating data. Leak-search before adding refrigerant, then repair, pressure-test, evacuate, and charge by the exact Daikin procedure and documented quantity/charging method.
Model-specific verification
Daikin VRV IV-S service literature lists U0 as refrigerant shortage. Detection logic and charging procedure vary by VRV family and model.
Manufacturer reference
Use the manufacturer source below together with the exact model and controller documentation for the equipment being serviced.
Daikin VRV IV-S Heat Pump Service ManualSafety note
HVAC work can involve high voltage, rotating equipment, pressurized refrigerants, and combustion systems. Use this site as a reference only. Follow the equipment manual, applicable codes, PPE, lockout/tagout, and current refrigerant rules. Field cases and troubleshooting paths are case-specific and are not OEM procedures or universal targets.