Diagnosing Air Conditioner Problems



Your air conditioning system needs periodic attention. Even so, problems can happen. Before calling for help, it’s possible to save time and money by doing some AC troubleshooting of your own.

AC Doesn’t Run

  • If your system doesn’t turn on at all, make sure it’s getting power. Check the fuse or circuit breaker. If your system has a secondary breaker near the outside unit, verify that it’s on.

Air Conditioner Turns On and Off Too Often or Not Often Enough

  • Your system cycles based on a sensor you know as the thermostat. Verify that it is set in the ‘cooling’ position. If it is located in a small, isolated room, other rooms may not cool properly. Consider moving it to a larger, more centrally located room.
  • If your system starts and stops frequently, it may be too big, or a register could be blowing on a thermostat.
  • If your system seldom cycles off, you could have low refrigerant levels or faulty relay switches.
  • Dirty filters and intakes can prevent your system from pulling in enough air to properly cool your home. Check your air filters and exchange them regularly to keep your home comfortable. Alternatively, consider upgrading to a media filter, which only requires semiannual attention.

Water Accumulating Under the AC

  • Pooling water in your AC unit’s drip pan could mean a broken condensation pump or a blocked drain line (if it’s the latter, you can try clearing the line with bleach). Either way, that water means it’s time to schedule service. You should consider installing a safety shutoff switch that will turn the unit off if drain lines back up.

AC Runs, But Doesn’t Blow Cool Air

  • If your system blows warm air, check that the outside unit is running, and that its airflow isn’t blocked by leaves or debris.
  • If the fan on the outside unit isn’t turning, turn the thermostat fan switch to the ‘off’ position. If the inside fan continues running, turn off your system breaker and schedule service. Your problem could be insufficient refrigerant. Your air conditioner is a closed system. If it’s low on refrigerant, you have a leak, which commonly occurs at valves or in the coil. Finding a leak is work for a professional.
  • If your blower motor is running but not cooling, your system is probably frozen, and needs professional attention.