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Why Is My AC Not Cooling? 8 Common Causes

If your air conditioner is running but the house just won’t get cold, the cause is usually one of a handful of things. Here’s how to tell what’s going on — and what’s safe to check before you call for help.

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Quick things to check yourself first

Before anything else, confirm the thermostat is set to Cool and below room temperature, and that it has working batteries. Then check the air filter — a clogged filter is the single most common cause of weak cooling and can even freeze the system. Finally, make sure the outdoor unit is running and isn’t buried in leaves or debris.

If the filter was filthy, replace it, switch the system off for an hour to let any ice melt, then try again. A surprising number of ‘broken’ AC units just needed a clean filter.

The 8 most common causes

1. Dirty air filter restricting airflow. 2. Low refrigerant from a leak. 3. Frozen evaporator coil (often caused by #1 or #2). 4. Dirty condenser coil outside. 5. Failing capacitor so the compressor or fan won’t start. 6. Thermostat problems or wrong settings. 7. Clogged condensate drain tripping a safety switch. 8. Leaky or undersized ductwork losing cooled air.

Numbers 1, 6, and the outdoor debris are homeowner-friendly checks. The rest — refrigerant, capacitors, coils, drains — need a technician with the right tools and training.

When to call a pro

Call for service if the system still won’t cool after a filter change and reset, if you see ice on the lines, if the outdoor unit won’t turn on, or if you hear loud electrical buzzing. During a heat wave, don’t wait — small problems get worse fast when the system is straining.

Ventroute connects you with an independent, licensed local AC repair tech in your area, often the same day. Just call (888) 616-5525.

Frequently asked questions

Why is my AC freezing up?

Almost always restricted airflow (dirty filter) or low refrigerant. Both make the coil too cold, so condensation freezes. Turn the system off to thaw it, replace the filter, and if it refreezes, call a pro to check refrigerant.

Should I run my AC if it's not cooling?

If it’s running constantly without cooling, shut it off and investigate — running a struggling system (especially a frozen one) can cause a more expensive failure.

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