AC Not Cooling? 6 DIY Fixes Before Calling HVAC

Your air conditioner is running but not cooling the house. Here are 6 things to check before spending $200+ on a service call.

Written by Mike Thompson

Licensed General Contractor · 20 years experience

HelpByExperts air conditioning troubleshooting guide for homeowners

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In this article

1. Fix 1: Check and Replace the Air Filter 2. Fix 2: Check the Thermostat Settings 3. Fix 3: Check the Circuit Breaker 4. Fix 4: Clean the Outdoor Unit 5. Fix 5: Check the Condensate Drain 6. Fix 6: Check for Ice on the Coils

Fix 1: Check and Replace the Air Filter

A dirty filter is the number one cause of AC problems. A clogged filter restricts airflow, causing the evaporator coil to freeze and the system to blow warm air. Check the filter — if you cannot see light through it, replace it. Filters cost $5–15 and should be changed every 1–3 months during heavy use.

Fix 2: Check the Thermostat Settings

Make sure the thermostat is set to COOL mode (not just FAN or HEAT). Verify the set temperature is lower than the current room temperature. Replace thermostat batteries if the display is dim or blank. Try lowering the temperature 5 degrees below room temp and wait 10 minutes.

Fix 3: Check the Circuit Breaker

AC systems have two breakers — one for the indoor unit and one for the outdoor unit. If only the indoor fan is running, the outdoor breaker may have tripped. Check your electrical panel and reset any tripped breakers.

Fix 4: Clean the Outdoor Unit

The outdoor condenser unit needs airflow to release heat. If it is clogged with leaves, grass, or debris, the system cannot cool efficiently. Turn off the AC, then gently hose down the outdoor unit from top to bottom. Clear any vegetation within 2 feet of the unit.

Fix 5: Check the Condensate Drain

AC units produce water that drains through a condensate line. If this line is clogged, some units have a safety switch that shuts down cooling. Find the drain line (usually a PVC pipe near the indoor unit) and flush it with vinegar or use a wet/dry vacuum on the outdoor end.

Fix 6: Check for Ice on the Coils

If you see ice on the indoor evaporator coil or the outdoor refrigerant line, turn the AC off and run only the fan for 2–3 hours to let the ice melt. A frozen coil is usually caused by low airflow (dirty filter), low refrigerant, or a failing blower motor. If it freezes again after thawing, call a professional.