Mitsubishi Mini-Split Not Cooling: Outdoor Unit, Refrigerant, and Sensor Fixes

Mitsubishi mini-splits not cooling have a different diagnostic approach than Daikin due to Mitsubishi's unique Hyper-Heating (H2i) technology and 3-wire communication system. First: check the remote control mode - ensure it is set to COOL (snowflake icon), not AUTO or DRY. Mitsubishi's auto mode can switch to fan-only if the room is near the setpoint. Second: go outside and check if the outdoor unit fan and compressor are running. If the outdoor fan runs but no compressor hum: the system may be in a defrost cycle (runs briefly then resumes), or the compressor has failed. Third: check for blinking LED patterns on the indoor unit - Mitsubishi uses a specific LED blink code system separate from any error code on the remote. Count the blinks of the OPERATION light and the TIMER light independently - the combination identifies the fault. Fourth: clean the indoor unit filters - Mitsubishi filters are behind the front panel and should be cleaned every 2 weeks during heavy use.