Air conditioner not cooling?

The system runs but the house stays warm. Most often it's a dirty filter, a thermostat setting, or a dirty outdoor coil; ice on the indoor refrigerant lines or an outdoor fan that isn't spinning point to bigger problems.

Not sure which one it is? Snap your ac and we’ll narrow it down.

Is the system not running at all?

That's a power or control problem rather than a cooling problem. Air conditioner won't turn on

Likely causes

  1. Dirty air filter

    Most commonEasy DIY

    Weak airflow at the vents, a filter grey with dust, or a house that cools slowly. A clogged filter can also freeze the indoor coil.

  2. Thermostat set wrong

    Most commonEasy DIY

    Not on Cool, the set temperature at or above the room temperature, or the fan on On instead of Auto, which blows warm air between cooling cycles. A dead battery or an unexpected schedule can do the same.

  3. Dirty or blocked outdoor coil

    CommonEasy DIY

    Leaves, grass clippings or cottony debris on the outdoor unit, or plants crowding it. The air is cool but not cool enough, and worse on hot afternoons.

  4. Frozen indoor coil

    CommonModerate DIY

    Ice on the copper refrigerant lines or the indoor unit, weak airflow, and water dripping when it thaws. Usually from a dirty filter, blocked vents or low refrigerant.

  5. Failed capacitor

    CommonCall a pro

    The indoor fan blows but the outdoor fan or compressor isn't running, or the outdoor unit hums without starting.

    Part: $100–400 (capacitor, installed)

  6. Low refrigerant or a leak

    Less commonCall a pro

    Air that's only slightly cool, ice on the lines, or hissing and oily residue on the refrigerant lines. Refrigerant doesn't get used up, so low means a leak.

    Part: $100–600 (recharge); $200–1,500 (leak repair)

  7. Failed compressor

    Less commonCall a pro

    The outdoor fan spins but the unit is loud, hot or tripping the breaker, and the air never gets cool.

    Part: $600–3,000 (compressor)

Quick checks

Switch off the breaker and the outdoor disconnect before touching the outdoor unit, and never reach into the fan. The capacitor stores a charge even with the power off, so capacitor and contactor work is for a pro. Refrigerant work needs a certified technician. For a frozen coil, switch the system off (or set the fan to On with cooling off) to thaw it, and never chip the ice. Reset a tripped breaker once only; if it trips again, call a pro.

  1. Check the thermostat is on Cool, the fan is on Auto, and the set temperature is below the room temperature.
  2. Replace the air filter if it's grey and clogged, and open every supply vent.
  3. Look at the outdoor unit: clear leaves and debris from around it and make sure the fan is spinning when the system is calling for cooling.
  4. Look at the copper lines at the indoor unit. If there's ice, switch cooling off and set the fan to On to thaw it, which can take a few hours.
  5. Heat pump? It's the same outdoor unit, so also see heat pump not heating and heat pump blowing cold air if the problem shows up in winter too.
Sharpen the read

Diagnose your air conditioner in seconds, for free

No account, no phone number. Fixology’s AI reads your photo and tells you what’s likely wrong, how worried to be, and whether it’s a DIY fix.

Snap one of these:

  • the outdoor unit, including the fan and coil
  • the thermostat display and mode
  • the indoor unit's refrigerant lines, especially any ice
  • the model label on the outdoor unit

Add a note or more photos next. Nobody calls you.

When to call a pro

The outdoor fan or compressor isn't running, ice returns after thawing, the air stays warm after the basic checks, you hear hissing, grinding or humming, or the breaker keeps tripping. For lifespan and upkeep, see the air conditioner guide.

Typical cost: $250–700 for most repairs (about $375), up to about $3,000 when the compressor is involved. Expect a minimum service fee of about $75, hourly rates of $75–175, and $150–300 for emergency calls. If a repair passes half the replacement price, replacing is usually the better move.

Sources: Fixr: How much does AC repair cost? (updated January 29, 2026)

After a scan, Fixology can also help you find pros near you.

Related problems

  • Air conditioner won't turn on?

    AC

    Nothing runs when cooling is called for, usually a thermostat issue, a tripped breaker or disconnect, or a clogged condensate line.

  • Furnace won't heat?

    FurnaceFall

    The furnace runs but the house stays cold, which is usually a clogged filter, a thermostat setting, or an ignition fault.

  • Heat pump not heating?

    Heat pumpFall

    The heat pump runs but the house stays cold, which is usually thermostat settings, a clogged filter, or an iced-over outdoor unit.

  • Washer won't drain?

    Washer

    Water is left in the drum after the cycle, which is usually a clogged pump filter or a kinked drain hose.

Fixology helps you understand your home — it isn't a substitute for a licensed pro on serious gas, electrical, or structural work.