AC Running but Not Cooling? 8 Things to Check Before You Call

It is the middle of a Texas afternoon, the AC is running, and the house keeps getting warmer. Before you call anyone, there are a few things you can check yourself in about ten minutes. Some of them fix the problem outright. The rest tell you, or your technician, exactly where to look.

One safety rule first: do not open the panels on the outdoor unit. The capacitor inside can hold a dangerous charge even with the power off.

1. Check the thermostat

It sounds too simple, but it is the most common fix.

• The mode is set to Cool, not Heat or Off.
• The fan is set to Auto. On “On”, the fan keeps blowing between cycles, and that air feels warm.
• The set temperature is below the room temperature.
• If it runs on batteries and the screen is faint or blank, replace them.

2. Check the air filter

A clogged filter starves the system of air. Less air across the indoor coil means less cooling, and in bad cases the coil freezes solid. Pull the filter. If you cannot see light through it, replace it and give the system an hour.

3. Check the breakers

Your AC usually has two power points: a breaker in the main panel, and a disconnect box on the wall next to the outdoor unit. If the outdoor unit is silent while the indoor fan runs, a tripped breaker is a likely cause. Reset it once. If it trips again, leave it off and call. A breaker that keeps tripping is protecting something.

4. Look at the outdoor unit

With the system calling for cooling, go outside and look.

• Fan spinning, unit running: good. Move on to the coil.
• Unit humming, fan not spinning: this is very often a failed capacitor, the part that helps the motors start. It is a common and fairly inexpensive repair, but it is a job for a technician because of that stored charge.
• Nothing at all: go back to step 3.

5. Check the outdoor coil

The outdoor coil is where your AC dumps the heat it pulls out of the house. When it mats over with dust, grass clippings, and pet hair, the heat has nowhere to go, and the system runs and runs without catching up.

We saw exactly this on a Fort Worth job: an AC running nonstop, a coil buried under what looked like felt, and cold air back within minutes of a wash. With the power off at the disconnect, you can gently rinse light dust off the outside of the fins with a garden hose. Never use a pressure washer, which bends the fins. Heavy buildup is worth a proper cleaning. More on that in our post on dirty AC coils.

6. Look for ice

Check the copper lines running into the outdoor unit and, if you can see it, the indoor coil. Ice means something is wrong, usually restricted airflow or low refrigerant.

Turn cooling off at the thermostat and set the fan to On so the ice melts. That can take a few hours. If the filter was the cause, a clean filter may be the whole fix. If the ice comes back, call.

7. Check the drain line and pan

Your AC pulls water out of the air, and that water drains through a small pipe. In many DFW homes, the indoor unit sits in the attic over a drain pan with a float switch. When the line clogs, the pan fills, and the float switch shuts the cooling off to protect your ceiling.

If the pan has water in it, or you see a fresh stain on the ceiling below the unit, that is your answer. We cleared one of these on an attic drain job where the pan was one overflow away from a ceiling repair. Line clogs are a routine fix when caught early.

8. Ask whether it is a leak

Refrigerant is not fuel. It does not get used up. If a technician tells you the system is low, the real question is where is the leak. A top-off without a leak search usually means paying for the same refrigerant again next summer.

When the house just cannot keep up

On the hottest DFW afternoons, even a healthy system can run nonstop and drift a few degrees above the setting, then catch up after sunset. That is usually the system working at its limit, not failing.

If it never catches up, even overnight, or it is getting worse each week, something above is likely the cause, or the system is undersized or leaking through the attic ducts. That is worth a visit.

When to stop and call

Call a technician if:

• the breaker trips more than once
• the outdoor unit hums but the fan does not spin
• ice comes back after you thaw it
• there is water in the drain pan or a new ceiling stain
• you smell burning or hear grinding or screeching
• the system has had the same problem before

What the common fixes cost

Fix	Lantern starts at
Condenser coil cleaning	$99
Drain pan and line clear	$165
Capacitor or contactor	$185
Refrigerant leak search and test	$299
Condenser fan motor	$525

These are starting prices. The final number is confirmed in writing before any work begins. If your system is older and the repairs are adding up, our repair or replace guide helps you decide.

Lantern serves homes across Dallas-Fort Worth. See our AC repair page, or call Lantern at (682) 337-0863.