How to Troubleshoot a Condensing Unit


An air conditioning condenser is an outdoor unit that works in conjunction with an indoor air handler to cool your home. The condensing unit liquefies vaporized cooling refrigerant and returns it to the blower to chill the air indoors. If your unit is not functioning properly, try troubleshooting your appliance to save money before calling a repairman.

Things You'll Need

  • Multimeter
  • Voltmeter
  • Check to see if the fan motor on the condensing unit is running. If not, turn the power off to the air condenser and check the wiring for signs of damage. Also check the connections in the terminal box for signs of burning or warping.

  • With the power off, check the start capacitor on the unit with a multimeter and replace, if necessary. If you see any bulging of the capacitor or an oily leakage, it probably needs to be replaced. (See Resources below.)

  • Return power to the unit, and check for a reset button or a high pressure switch that may have cut off power to the condenser. Reset if needed.

  • Test if power is going to the unit with a voltmeter. If there is none, check the wiring to see if it has been burned or interrupted. There should also be 24 vac going to the contactor coil; if not, check the thermostat and the wiring from the air handler/blower to the condenser unit. If there is both power going to the unit and the contactor, you may have a bad unit contactor.

  • Check the compressor; if it is running without the fan, check to see if the fan motor needs to be replaced. If the compressor fan runs, but the compressor itself is not working, check the refrigerant levels. If they are okay, you may need to replace the compressor unit.

Tips & Warnings

  • Regular yearly service of your condensing unit will keep it running more efficiently.
  • Never attempt repairs on a condensing unit if you are unsure of what you are doing.

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