3 Ways A Digital Multi-Meter Can Help You Diagnose A Non-Functioning AC Condensing Unit

The condensing unit in a central air conditioning system is where the cooling process begins once the thermostat is dialed down. A compressor is kicked into action and produces a gas refrigerant required to fuel the entire cooling process. Problems in the initial stages of condensing unit function can thwart your entire system and leave you with warm, uncomfortable air inside your home.

There are a number of parts inside the condensing unit that can go bad. But using a digital multi-meter can help you troubleshoot and determine whether one of three important parts are what is causing the failure.

Start and Run Capacitors

Start and run capacitors are both parts meant to hold an electrical current and give the compressor some help where needed. The start compressor gives a boost when the system first triggers into action and the run capacitor is on standby in case there's an electrical interruption that could shut down the compressor. A problem in one or both of the capacitors can keep the compressor from turning on or can make the compressor turn on then off quickly.

You can test the start and run capacitors using your digital multi-meter and its Ohms settings. But first you need to do a bit of prep work since the capacitors store electricity.

Turn off the main power to the condensing unit at the fuses or breakers. Now you need to discharge the capacitors. You can discharge the run capacitor by laying the end of an insulated screwdriver over the capacitor's terminals for a few moments. Discharge the start capacitor by unhooking its wires, hooking up the multi-meter probes, and then turning the multi-meter to AC setting. Wait until the AC reading hits zero and the start capacitor is discharged.

Testing works the same on both capacitors. Hook up the multi-meter probes to the terminals on the capacitors and set the machine to the Ohms reading. Locate the Ohms listing printed on each capacitor to see what the target range is for the reading. If the reading doesn't match the range, you need to replace the part.

Compressor Testing

You can also test the compressor itself though the testing is a bit trickier. If you have any doubts about the process, call in an air conditioning repair company like JV Systems Air Conditioning And Heating of Tampa Bay Inc for help.

Set the multi-meter to continuity testing mode. On many digital multi-meters, this mode means that the meter will beep if there is continuity and won't beep if there isn't. Note that a beep alone doesn't mean that your compressor is fully functioning but it can be an indication that the problem is elsewhere in your condensing unit.

Conduct the test by locating the terminals on the compressor, which should have letter labels of C, R, and S. You want to hook your multi-meter probes to each pair of these terminals and wait for the beep. Continue on to the next pair if you do hear the beep. Start with C and R, then R and S, then C and S to ensure all pairs are tested.


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