AC running but not cooling? What to check first

What are the first three things to check?

Before you call anyone, take five minutes on the basics. Go to the thermostat. Confirm it is set to Cool, the fan is on Auto, and the set point is a few degrees below the room. If it runs on batteries, swap them. If the screen is blank, that is your problem right there.

Next, pull the filter. A filter clogged with dust chokes the airflow, and without airflow the indoor coil cannot pull heat out of the house. Hold it up to a light. If you cannot see through it, replace it.

Then check the electrical panel. There are usually two breakers, one for the indoor blower and one for the outdoor condenser, plus a disconnect box on the wall next to the outdoor unit. A tripped breaker sits between On and Off. Reset it once. If it trips again, leave it off and call.

Is the outdoor unit running and clear?

Walk outside. The condenser fan should be spinning and blowing warm air upward, and you should hear the compressor humming. If the fan is still but the unit buzzes, a failed capacitor is a common cause, and that is a technician repair.

Then look around it. The condenser gets rid of the heat pulled from your house, and it needs open air to do it. Shrubs that have grown in, a fence panel too close, mulch piled against the base, or a summer's worth of cottonwood fluff on the fins all trap heat and push the system toward overheating.

• Keep about two feet of open space on all sides and nothing stacked on top.
• Turn the power off at the disconnect before touching the unit.
• Rinse the fins gently from the inside out with a hose. No pressure washer.
• Straighten a level pad if the unit is tilting, since a tilt strains the compressor.

Why is there ice on my AC, and what do I do?

Ice on the larger copper line at the outdoor unit or on the indoor coil means the coil got colder than it should. The two usual causes are low airflow, from a dirty filter or a failed blower, and low refrigerant, which points to a leak. Either way the ice blocks airflow, which makes more ice.

Turn the system to Off at the thermostat, switch the fan to On, and let it thaw for several hours. Put towels around the indoor unit because melting ice drips. Do not chip at the ice. Once it is clear, change the filter and try again. If it ices up a second time, leave it off and call, because continuing to run it can send liquid refrigerant back to the compressor and damage it.

Did the condensate float switch shut it down?

Central AC pulls moisture out of the air, and that water drains through a small PVC line. When algae or dust clog the line, the drain pan fills, and a float switch in the pan cuts power to the system on purpose. That protects your ceiling or basement floor from a leak. The symptom is an AC that will not start at all, or that starts and quits, with a full pan under the indoor unit.

You can look for a pan with standing water and a small switch with a float on it. Clearing the line usually means blowing it out or vacuuming it from the outdoor end. Some homeowners handle this themselves; if you would rather not, it is a quick fix for us and part of every AC tune-up.

When should I stop and call?

Call when you have done the basics and the house is still warm, when a breaker trips a second time, when the outdoor unit buzzes without the fan turning, when ice comes back, or when the air from the vents feels cool but the house never catches up on a hot afternoon. That last one often means the system is losing refrigerant slowly and a leak search is needed.

One rule protects the most expensive part of your system: if the AC is iced or clearly struggling, turn it off rather than letting it run. A compressor that is cooked by running dry or flooded with liquid is the difference between a repair and a replacement. Request AC repair service and we will diagnose it, show you what we find, and give you options.