My A/C Won’t Start Up, Just Clicks

2017 Mar 27
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If your A/C won’t start and all you get is a repetitive clicking noise at the outdoor unit, the problem is either a faulty contactor or capacitor.

Not sure what either of those parts are? Don’t worry. We’ll explain what a capacitor and contactor are, why they’re clicking and how they’re preventing your A/C from starting.

Note: Unfortunately, repairing these parts requires a professional, but we can help you determine which part needs repair before you call a tech. If you live in Phoenix and need a tech now, just contact us. We’ll send over a professional right away.

1) Check your capacitor

What your capacitor does:

Your capacitor is housed inside your outdoor unit and acts like a giant battery that gives your A/C compressor the extra voltage it needs to start up. Fun fact: your A/C probably needs up to 3 times the amount of power at start-up than it uses to run.

Not all A/Cs have capacitors to help them start up, though. Usually, capacitors are installed on older A/Cs that need a little extra help to start.

But, over time, capacitors lose their charge (just like how batteries lose their charge) and can no longer give your A/C the kick-start it needs to turn on. So when the capacitor on an older A/C goes bad, the system won’t have the amount of power it needs to start up until the capacitor is replaced.

Learn more about bad capacitors by checking out our blog, “My A/C Just Hums and Buzzes But Doesn’t Turn On”.

How to diagnose a bad capacitor

If you hear a clicking noise followed by a soft hum or buzzing noise but your outdoor unit doesn’t turn on, you probably have a bad capacitor that needs to be replaced. The “buzz” you hear is the motor trying to turn on without help from the capacitor.

Other signs of a bad capacitor:

  • Bottom or top of capacitor is bulging
  • Visible gooey discharge on the capacitor

2) Check your contactor

What your contactor does:

Your contactor sits on the outdoor unit and is basically a big relay that turns the unit on and off.

Your contactor is the “middleman” between the thermostat and your compressor. Once the thermostat sends the command for cooling, your contactor kick-starts the process of starting your compressor.

But if it’s gone bad, it can’t execute the commands sent from your thermostat, and your A/C won’t start. So that clicking you hear is the unanswered signal from the thermostat.

How to diagnose a bad contactor:

If your outdoor unit won’t come on and all you hear is a click (but no humming or buzzing), your contractor is likely the problem.

Need a professional to diagnose your clicking A/C?

If you live in the Phoenix area and need a professional to repair your A/C, we’re here to help.

Just contact us and we’ll send over a tech right away.


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