AC Running But Not Cooling: What to Check First

Start at the indoor unit

Two minutes here resolves a genuine share of calls.

Pull the filter out

Hold it up to a light. If you cannot see through it, that is very likely your answer. A restricted filter starves airflow across the evaporator coil, the coil temperature drops below freezing, and ice forms — and a frozen coil moves no heat at all. The classic pattern is a system that cooled fine for an hour and then stopped.

Look for ice on the copper line

Where the insulated copper line meets the indoor unit. Frost or a solid collar of ice confirms a frozen coil. Switch the system to FAN ONLY — not off — for two hours to thaw it, change the filter, then try cooling again. If it freezes again within a day, the cause is refrigerant rather than airflow and it needs a technician.

Check the thermostat is actually asking for cooling

Set to COOL, fan on AUTO, setpoint genuinely below room temperature. With the fan set to ON the blower runs continuously between cooling cycles, moving room-temperature air, which people reliably read as a failure.

Then go outside

The outdoor unit is where the heat is supposed to leave. If it cannot, nothing else works.

Is it running at all?

Fan spinning, compressor humming. If the indoor blower runs and the outdoor unit is silent, that is your fault located — a tripped breaker, a pulled disconnect, a failed capacitor or contactor, or a safety cutting it out. A unit that hums without the fan turning is the classic failed capacitor.

Is the coil clogged?

Late June is peak cottonwood season in New Jersey and the seed mats onto a condenser coil like felt. Grass clippings do the same. A blocked coil cannot reject heat, so the system runs constantly and never quite reaches setpoint. Switch off at the disconnect, then rinse the coil from the inside outward with a garden hose. Never a pressure washer — it folds the fins flat and makes it permanently worse.

Is there clearance around it?

Two feet all round, nothing growing into it, nothing stacked on top. Shrubs planted to hide the unit are a common and self-defeating cause.

What is left is a technician job

If the filter is clean, the coil is clear and the outdoor unit runs, two causes remain and both need equipment you do not have.

Low refrigerant, which means a leak

Refrigerant is not consumed — it circulates in a sealed system. A system that is low has a leak somewhere, and adding more without finding it is buying the same repair again next summer. Anyone who tops it up without proposing a leak search is selling a temporary result. Near the shore, corrosion is usually the underlying cause.

A failing compressor

The expensive one. Symptoms include the outdoor unit tripping the breaker on start, loud grinding, or a unit that runs but produces no temperature difference across the coil. On an older system this reopens the replacement question outright — and on an R-22 system it usually settles it.

The one that is not a fault at all

If the house reaches temperature quickly but feels damp and clammy, the system is very likely oversized rather than broken. It satisfies the thermostat before it has run long enough to remove humidity, so the air is cold and wet.

Turning the thermostat down makes this worse, not better. It is a sizing problem, and in New Jersey's humid summers it is the most common complaint after a badly specified replacement.