Mitsubishi MSZ-GL09NA 9,000 BTU Wall-Mount Ductless Mini-Split Indoor Unit U1 Error Fix: Power Supply Phase / Momentary Power Failure

Error code U1 on the Mitsubishi MSZ-GL09NA 9,000 BTU Wall-Mount Ductless Mini-Split Indoor Unit means: Power Supply Phase / Momentary Power Failure. The system has detected a momentary power interruption or phase anomaly in the electrical supply. Common causes include brief power outages, brownouts, lightning-induced transients, or unstable mains supply. On 3-phase commercial units, this can indicate phase loss. The system will attempt to restart automatically after the power stabilizes. If U1 recurs frequently, install a dedicated circuit with proper grounding and consider a surge protector or power conditioner.

The most successful fix is "Install Dedicated Circuit and Surge Protector" (medium difficulty, ~90 minutes). Estimated DIY cost: $50-$100. HomeMD has 2 community-ranked fixes for this error.

This error is rated medium severity. It should be addressed soon, but your appliance may still function in a limited capacity.

Yes — the top-ranked community fix ("Install Dedicated Circuit and Surge Protector") is rated medium difficulty and takes about 90 minutes. Tools needed: Voltage tester, Wire stripper, Screwdrivers, Drill with bits.

DIY cost: $50-$100. Professional repair typically costs $200-$350. Many homeowners save money by trying the top-ranked community fix first.

The Mitsubishi MSZ-GL09NA 9,000 BTU Wall-Mount Ductless Mini-Split Indoor Unit has 8 other known error codes, including: E1 (Remote Controller PCB Error), E2 (Remote Controller Signal Receiving Error), E3 (Remote Controller Communication Error), E4 (Indoor Unit PCB Processor Error), E5 (Indoor/Outdoor Communication Error (Legacy)), and 3 more.

Error code U1 also appears on 14 other Mitsubishi models: MLZ-KP09NA 9,000 BTU One-Way Ceiling Cassette Indoor Unit, MSZ-EF15NA 15,000 BTU Designer Series (Kirigamine Zen) Wall-Mount Indoor Unit, MSZ-FH12NA 12,000 BTU Hyper-Heat H2i Wall-Mount Indoor Unit, MSZ-FS06NA 6,000 BTU Compact Wall-Mount Indoor Unit, MSZ-GL12NA 12,000 BTU Wall-Mount Ductless Mini-Split Indoor Unit, MUZ-GL09NA 9,000 BTU Single-Zone Outdoor Unit, and 8 more. The fix may vary by model, so check each model's specific page for tailored repair steps.