Indoor unit displays F0 and system will not operate normally.

Safety first: Do not attempt to add refrigerant yourself unless you are licensed. Turn off power before inspection.

User checks:

• Inspect flare connections: At both indoor and outdoor units, look for oil residue around the flare fittings on the line set. Oil stains often indicate a leak.
• Check insulation: Ensure the suction line insulation is intact and not saturated with oil.
• Listen for hissing: In a quiet environment, listen near connections for a faint hissing sound that might indicate an active leak.

Professional repair: F0 almost always requires a licensed HVAC technician to locate leaks, repair or replace the refrigerant line set or coils, evacuate, and recharge the system to MrCool specifications.