Weak airflow is the easiest symptom to fix and the most damaging to ignore - it quietly causes half the other problems on this site, from frozen coils to short cycling. Work the list; most cases end at the filter.
Safe checks first
- Filters. The cause in most homes. If you can't remember cleaning them, that's the answer. Rinse, dry fully, reinstall.
- Fan speed and mode. AUTO fan at mild setpoints runs deliberately slow; QUIET/NIGHT modes cap the blower. Set fan to HIGH manually and compare - a strong HIGH means settings, not fault.
- Louvers and swing. A louver parked nearly closed (or a swing motor stopped in the wrong position) chokes and misdirects supply air. Cycle the vane control; if a louver never moves, note it for the technician (small motor, cheap part).
- Coil face check. Filters out, look at the coil: a gray felt of dust on the fins passes some air and blocks the rest. Surface-vacuum gently with a brush; matting deeper than the surface needs a professional coil clean.
- Ice check. Weak flow + cold room + ice sheen = frozen coil - go to that page's thaw-first steps.
- Blower wheel (look, don't disassemble). With power OFF, peer past the louvers with a flashlight: the squirrel-cage wheel's fins packed with dust dramatically cut airflow and add a damp-dust smell. Cleaning it properly is panel-off technician work.
Beyond the safe checks (technician scope)
Blower-wheel deep cleaning, fan-motor or drive-board faults (speeds hunt, or HIGH sounds no different from LOW), duct-kit static issues on concealed-duct units, and any airflow loss paired with fan-speed error codes (EH 03 class - check the library).
When to stop and call
Fan speed codes that return after a power cycle; a blower that squeals, grinds, or wobbles audibly; airflow that stays weak after clean filters and HIGH fan - the remaining causes all live behind the panel.
Sources
No model-specific systems are linked from this guide yet.