How To Test The Start Capacitor On A Window Air Conditioner That Won't Run

Air conditioners have two capacitors that provide electrical surges to help the system run and run efficiently. When you turn down the thermostat, the start capacitor provides the energy boost that gets the motor running. A failing or failed start capacitor can keep your unit for working efficiently or at all.

If you have some electrical experience and appropriate equipment, you can test the start capacitor for functionality. 

Make sure you unplug the unit and take it out of the window before you perform any work on the window air conditioner.

What You Need:

  • Air conditioner user's manual
  • Screwdriver
  • Insulated pliers
  • Ohmeter  

Step 1: Access and Unhook Capacitor

Consult your owner's manual to find out exactly where the start capacitor is located within your unit. The location can vary wildly between models and you want to know where to look before you open the unit as you don't want to accidentally work on the run capacitor.

Remove the front panel of your window air conditioner by unscrewing the fastening screws. Find your start capacitor. Use the insulated pliers to remove the wires from the terminal connectors on the capacitor so that you can hook on your ohmmeter for testing.

Step 2: Discharge the Capacitor

Capacitors can hold an electrical charge even while the unit is unplugged. You need to remove that charge before testing so that you don't accidentally electrocute yourself or blow the fuse for the capacitor.

Discharge the capacitor by turning your ohmmeter to the AC position. Touch the ohmmeter leads to the capacitor's terminal connectors. Hold the leads there until the ohmmeter reads zero on the AC setting then remove the leads. You can then switch the meter over to the Ohms for the actual test.

Step 3: Test the Capacitor

Double check that you have the ohmmeter set correctly for an Ohms test, which should include moving a lead into the Ohms position. Consult your meter manual if you need some help setting things up.

Hold the leads to the capacitor terminal connectors. If the Ohms slowly climb, then there probably isn't a problem with your start capacitor. If the Ohms leap up, your capacitor has an open circuit and needs replaced.  Did you receive no Ohm reading whatsoever? The capacitor is broken and needs replacing.

 Don't have electrical experience? Leave this check in the hands of a professional air conditioning repair technician. Call an HVAC tech (like those at American Heating & Air) to test your capacitor and save yourself some trouble and potential injury.

About Me

Perfecting My Home HVAC System

After dealing with almost constant air conditioner and furnace failures, I realized I might not be doing my part to keep my systems clean and operational. To sort out the issues, I turned to a professional repairman for help. He explained that since I wasn't changing the filters regularly, there was no telling what would happen. I learned how to clean evaporator coils, replace filters, and even sort out power failures on my own. I want other people to experience the confidence and comfort that comes along with protecting your own HVAC system, so I put up this blog.