Why Is My AC Running But Not Cooling?

An air conditioner that runs constantly without cooling is usually failing at one of two things: moving enough air, or moving enough heat. The first category contains most of the fixes you can safely do yourself.

Check these first

1. The filter. A clogged filter is the single most common cause and the cheapest fix. If you can't see light through it, replace it.
2. The thermostat. Confirm it's set to 'cool', the setpoint is genuinely below room temperature, and the fan is on 'auto' rather than 'on' — 'on' circulates uncooled air and feels like a failure.
3. Return and supply vents. Blocked returns starve the system; furniture and rugs are frequent culprits.
4. The outdoor unit. It rejects heat outside, so it needs clear space. Clear leaves, grass clippings, and anything growing against it.
5. The condensate drain. A backed-up drain can trip a safety switch and stop cooling entirely.

Symptoms that mean stop

Why 'low on refrigerant' is a red flag, not a service item

Refrigerant circulates in a sealed loop. It isn't consumed, so a system that is low has leaked. Any contractor who offers to top it up without finding the leak is selling you the same repair again next summer.

When the cause is the house, not the unit

• During extreme heat, systems are sized to hold a temperature difference, not to reach any setpoint — a house may simply be at the limit of what the equipment can do.
• Leaky ducts in a hot attic can lose a large share of the cooling before it reaches a room.
• An oversized unit cools air fast but removes little humidity, leaving a house that reads cool on the thermostat and feels clammy.

What to do next

Work down the safe checklist above in one pass — filter, thermostat, vents, outdoor unit, drain. If none of them changes anything, note exactly what you observed before calling a technician: the symptoms you can describe usually shorten the diagnosis and the bill.