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Troubleshooting Your Central Air

Split-system central air conditioners, used with forced air furnaces, take hot air from the house and blow it through an evaporator coil located in the top of the furnace to cool the air. The cooled air circulates throughout the house via the heat ducts then returns to the furnace as warm air to be cooled again.

Central air conditioners can work for years without problems if properly maintained and serviced annually. If they aren’t working properly, call a trained technician. But before you phone, see if the problem is caused by something else.

The unit stops working

If you have your system inspected and cleaned annually, it should run without any trouble. However, if it stops working completely and you aren’t sure why, troubleshoot before calling a pro:

  • Check the circuit breaker or fuse box to find out whether the unit has power.

  • Check the fuses in the disconnect box located outside, near the condenser, to make sure there’s power.

  • Replace or clean the furnace filter.

  • If the condenser coils are coated with dust or debris, use a garden hose to wash them off.

  • If the air conditioner still won’t work, make the call. A technician may have to recharge the refrigerant.

The unit won’t quit running

If the air conditioner runs constantly, here’s what to do:

  1. Turn up the thermostat.

    If you set the thermostat a few degrees higher, you will save energy and a lot of money when it comes time to pay your electric bill. And your significant other won’t have to complain about wearing a sweater indoors.

  2. Take the cover off the condenser and find out whether anything is blocking the air flow.

  3. Vacuum the interior of the condenser, and then flush it with a garden hose.

  4. If the fan blades are bent or dirty, straighten them out and/or clean them.

  5. While the cover is off, oil the motor on older air conditioners. (Newer units are sealed and cannot be oiled.) Take off the plastic covers — there should be two — and put a couple drops of lightweight oil, such as 3-in-1, into each.

  6. Replace the cover.

  7. Check the furnace filter and blower to see whether they’re blocked. Use a vacuum cleaner to clean dust and dirt on or around the blower.

  8. Replace the filter if necessary.

The unit freezes up

If the high pressure lines from the condenser to the furnace or the evaporator coil in the top of the furnace are iced up, then shut the system down:

  1. Either turn off the breaker in the panel or pull the disconnect switch outside at the condenser.

  2. Call for service. Your system is probably low on Freon and needs to be recharged.

Water pools under the evaporator

When there’s water under the evaporator at the base of your furnace, the drain is probably clogged. You can clear it, but it’s probably easier just to replace the whole thing. If you want to try clearing it, however, here’s what to do.

  1. Take off the trap, and if it’s PVC (plastic) you can cut the pipe to remove it.

  2. Pour a vinegar-water or bleach-water solution (1 to 10 parts) into the drain. That will help remove debris and algae.

  3. If you have flexible tubes, take them off and clean them by pouring the solution through them. You can also run a wire through the tube to scrape the walls. Do it gently so you don’t poke a hole.

  4. Reassemble the tubes and trap.

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