Safe checks first (no tools, no panels opened)
- Mode and setpoint. Confirm the remote shows COOL (snowflake), not FAN, DRY, or AUTO - and the setpoint is at least a few degrees below room temperature. (DRY dehumidifies but barely cools; AUTO can decide the room is fine.) If the display shows two letters like DF or CP, check the error-code library - some displays are status, not faults.
- Filters. Slide the front panel up and check the mesh filters. A clogged filter is the single most common cause of weak or warm airflow. Rinse, dry, reinstall - and note the airflow difference.
- Outdoor unit. Is the fan spinning? Is the coil packed with cottonwood fluff, leaves, or grass clippings? Gently rinse the coil with a garden hose (power off at the breaker first). Blocked outdoor coils can't reject heat.
- Power cycle. Breaker off five minutes, then on. Inverter boards occasionally latch a protection state that a clean restart clears.
- Check the display for a code. Anything alphanumeric on the indoor unit maps to a specific fault - look it up before calling; you'll have a better conversation with the technician.
Likely causes beyond the safe checks (technician scope)
- Low refrigerant / leak. Gradual cooling loss over weeks, ice on the small copper line, or a hissing indoor unit point here. This is not a DIY top-up - A2L-class refrigerants (R-454B, R-32) require certified handling, and the leak must be found and fixed, not just refilled.
- Frozen evaporator coil. If the indoor unit is iced, cooling stops. Ice is a symptom (airflow or refrigerant), not the disease. Power off, let it thaw fully, address the filter; if it re-freezes, call.
- Failed outdoor fan or capacitor-class components. Compressor runs, fan doesn't (or vice versa) - stop running it and call; continued operation cooks the compressor.
- Control/sensor faults. Usually announced by an error code.
Prevent the next one
Filters monthly in heavy season; outdoor coil rinse each spring; keep two feet of clearance around the outdoor unit. That routine prevents the majority of "not cooling" calls we see documented in service manuals.