Why Is My AC Not Cooling? 12 Causes and What to Check First

Start with the three free checks

Before anything else: set the thermostat to COOL and drop it five degrees, replace the air filter if it is grey, and walk outside to confirm the condenser fan is spinning. A shocking share of AC not cooling calls are a filter so clogged the coil froze, a thermostat switched to FAN ON, or a tripped breaker. These cost nothing to rule out.

1. Failed capacitor

The single most common AC repair we perform. A capacitor gives the compressor and fan motor the jolt they need to start. When it weakens, you hear a hum or click outside but nothing spins, and the indoor blower keeps pushing warm air. It is an inexpensive part and a fast fix.

2. Dirty condenser coil

The outdoor coil rejects heat. Pack it with cottonwood, grass clippings and dryer lint and the system cannot dump heat, so pressures climb, cooling drops and the compressor runs hot. A professional coil cleaning often restores full capacity.

3. Low refrigerant from a leak

Refrigerant is not consumed - if it is low, it leaked. Symptoms include weak cooling that gets worse over weeks, ice on the line set, and a hissing sound. Topping off without finding the leak is throwing money away; we locate and repair, then weigh in a correct charge.

4. Frozen evaporator coil

Restricted airflow or low charge lets the indoor coil drop below freezing. Once it ices, airflow stops entirely and you get warm air. Turn the system to FAN ONLY for a few hours to thaw, then get the cause fixed - it will refreeze otherwise.

5. Bad condenser fan motor

If the compressor runs but the outdoor fan does not, the unit will overheat and trip on high pressure, cooling in short useless bursts. Bearings, windings and capacitors are all common failure points.

6. Clogged condensate drain

A blocked drain fills the pan and trips the float switch, shutting the system down as designed. You may find water near the air handler. Fast, cheap fix - and yearly maintenance prevents it.

7. Failing compressor

The expensive one. A grounded or seized compressor draws high amps, trips breakers and produces no cooling. On a system over 12 years old, replacement usually beats repair. We show you both numbers.

8. Leaky or crushed ductwork

If ducts run through a hot attic and leak 25 percent of the air, you paid to cool the attic. Sealing and repairing ducts often improves comfort more than new equipment.

9. Oversized or undersized equipment

An oversized AC cools the thermostat fast, shuts off, and never runs long enough to remove humidity, so the house feels clammy. An undersized unit never catches up on the hottest days. Proper load calculation at installation prevents both.

10. Thermostat problems

Dead batteries, a loose C wire, a failed relay, or a thermostat mounted in direct sun will all produce strange behavior. Cheap to fix, easy to overlook.

11. Blower motor or wheel issues

A slipping belt, seized bearings or a blower wheel packed with dust cuts airflow drastically. You will feel weak air at every register.

12. Blocked or closed vents

Closing registers to redirect air raises static pressure and can freeze coils and burn out blowers. Keep vents open and returns clear.

When to stop and call

Call for AC repair immediately if you smell burning, see ice on the refrigerant lines, hear grinding, notice water damage, or the breaker trips repeatedly. Repeated breaker resets can destroy a compressor. Emergency AC repair is available 24/7 in every city we serve.