Why is my air conditioner not cooling well?

Start with airflow and the outdoor unit. A loaded filter, blocked condenser or blocked returns explain a large share of weak cooling. Refrigerant and electrical faults are not DIY territory.

Last reviewed 2026-07-15

If the indoor coil or refrigerant lines are frosted, turn the system to fan only and let it thaw before doing anything else; running it iced can damage the compressor.

A system that runs continuously in extreme heat but holds a reasonable indoor temperature may simply be sized for milder conditions rather than faulty.

What to check first

  • Filter condition and register or return blockages
  • Outdoor condenser clear of debris, vegetation and matted fins
  • Thermostat mode, setpoint and battery
  • Condensate drain not backed up, which can trip a safety switch
  • Breaker or outdoor disconnect not tripped

When to call a professional

  • Ice forms on refrigerant lines or the indoor coil repeatedly
  • The outdoor fan does not run, or the unit hums without starting
  • You suspect low refrigerant charge — charging is regulated work