When your central air conditioner is having problems starting up properly, the condensing unit access panel is a good place to start your troubleshooting. Behind the access panel, you will find a few of the key condensing unit parts that can cause startup issues: capacitors, the contactor, and the wires attached to both.
You can check the health of the parts yourself if you have a bit of electrical knowledge and a multi-meter. If you don't feel comfortable at any point during the process, make sure you call in an experienced air conditioning repair service technician from a company like Doctor Fix-It.
Plan to go solo? Consult your owner's manual before beginning to make sure you know exactly where all the parts are in your particular unit. You should also turn off all power to the unit at the fuse box or circuit breaker before you begin.
The first thing you want to check is the wiring inside the access panel. You don't need to do any detailed checks right now. Perform a visual inspection to see if there are any wires that look damaged in any way. If you see wires that look chewed through or singed, leave the power off to your unit and call in an emergency HVAC technician to fix the wiring.
You can also check to make sure the wires are all properly attached. You can check in greater detail once you begin examining the actual parts, but make sure there aren't any dangling wire connectors that suggest a wire has come loose from its terminal. Trace a loose wire back to its nearest component, look for an empty terminal, and then plug it back in.
You might want to turn your system back on right away and check for functionality. Sometimes the problem is as simple as an unhooked wire.
Your air conditioner will have one or two types of capacitors that help provide extra electricity to both help the compressor start running and to keep running without interruption. The capacitors are called the start capacitor and run capacitor, respectively.
You can test the capacitors for functionality using a multi-meter set to Ohms and using the handy Ohms range printed on the side of the capacitors. But first you want to remove any stored electricity that remains in the capacitor.
For a start capacitor, you can remove the energy by turning your multi-meter to AC. Remove the wires on the capacitor and hook the multi-meter probes to the terminals. Watch the reading until the AC reading drains down to zero. You can then proceed with the testing.
A run capacitor is simply drained using the end of an insulated screwdriver. Remove the capacitor wires and lay the end of the screwdriver across both terminals for a few moments. You can then use the multi-meter to double check that the charge is gone before proceeding.
The contactor is essentially the step between the indoor thermostat sending an electrical signal to start the unit and the compressor starting up. A failing or broken contactor can stop the unit from starting up properly.
You can check the contactor's health if you have a multi-meter with a continuity setting. Remove the wires for the contactor and attach the probes to two of the terminals. Wait to see if the meter beeps. If the meter doesn't beep, there isn't continuity in the contactor and you need to call in an HVAC contractor for a replacement part.