If your AC is running but not cooling the house, start with airflow and settings before assuming the system is dead. Check the thermostat, filter, vents, outdoor unit, ice, and condensate drain. Then stop if you see signs of an electrical, refrigerant, or mechanical problem.
Quick checks first
- Make sure the thermostat is set to cool and the temperature is below room temperature.
- Check whether the HVAC filter is dirty.
- Confirm supply vents are open and return grilles aren't blocked.
- Look outside and make sure the outdoor unit is running.
- Clear leaves, weeds, and debris around the outdoor unit.
- Look for ice on refrigerant lines or the indoor coil area.
- Check for water near the indoor unit or a full emergency pan.
- Call for service if the breaker trips, the unit buzzes, ice forms, or cooling doesn't return.
Check the thermostat
Start with the easy settings. The thermostat should be on cool, not fan or heat. Set the temperature several degrees below the current room temperature and wait a few minutes.
If the thermostat uses batteries, replace them if the display is weak or blank. If the system follows a schedule, make sure it isn't holding a higher set point than expected.
Check the air filter
A dirty filter can restrict airflow enough to make the system cool poorly. In some cases, low airflow can contribute to ice on the evaporator coil.
Turn the system off, remove the filter, and replace it if it is visibly loaded, gray, bowed, or the wrong size. Install the new filter with the airflow arrow pointing toward the furnace or air handler.
Check vents and returns
Open supply vents and make sure rugs, furniture, curtains, or storage aren't blocking returns. A closed off room or blocked return can make the system behave worse than it should.
Don't close a lot of vents to force cooling elsewhere. That can increase pressure in the duct system and create other problems.
Check the outdoor unit
Go outside while the AC is calling for cooling. The outdoor unit should be running, and the fan should be spinning. Clear leaves, weeds, grass clippings, and anything stored too close to the unit.
If the outdoor unit is silent while the indoor blower runs, the problem may be a breaker, disconnect, capacitor, contactor, wiring issue, or control problem. Don't open electrical panels unless you are qualified.
Look for ice
Ice on the refrigerant line or indoor coil area usually means airflow, refrigerant, or mechanical trouble. Turn the cooling off and set the fan to on if your system supports it. Let the ice thaw before service.
Don't keep running cooling mode over ice. It won't cool properly and can make the problem worse.
Check condensate drainage
Air conditioners remove moisture from indoor air. If the condensate drain clogs, a float switch may shut the system down or water may collect in a pan. Look for standing water near the indoor unit, a wet ceiling, a full emergency pan, or musty smells.
When to call HVAC service
- The breaker trips repeatedly.
- The outdoor unit hums or buzzes but the fan doesn't spin.
- Ice forms on lines or the indoor coil area.
- The system blows warm air after basic checks.
- There is water where it should not be.
- You smell electrical burning or see damaged wiring.
- The system is old and has been struggling for more than one season.
Good maintenance rhythm
- Monthly in cooling season: check the HVAC filter.
- Spring: clear the outdoor unit and test cooling before hot weather.
- After storms: clear debris around the outdoor unit.
- As needed: schedule service for ice, electrical issues, weak cooling, leaks, or repeated breaker trips.