HVAC troubleshooting 220V

Hello, Before I call the pros, I am going to do some basic troubleshooting on my central AC. The fan and compressor are not coming on. I can hear a low-voltage hum. I will start with a meter to make sure 220v is getting to the contactor and also 220v is coming out of the contactor. . Since I don't have any experience with 220v, I would prefer to not belt myself. Out of the wall is a pink and black wire to the contactor. Where do I put the meter leads to test it? Any danger moving the leads from terminal to terminal as long as I don't hold the leads by the metal end (just kidding). Also, when the unit comes on, should I see the contactor move, or click, or what?? I didn't see anything like that, so I am thinking 220v is not getting to the unit. . Thanks for your time. -jack
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If you have someone turn the thermostat up and down, you will hear the contactor click in and drop out. It operates on 24 volts which it gets from the blower unit. Near the condenser should be a disconnect. open the disconnect and find the two terminals marked "line". If you touch the terminals of a meter across these two terminals you should get 240 volts. If not, check the breaker feeding the condenser

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OK, this is going to sound nuts...The contactor was not clicking on. Out of frustration, I banged the side of the unit (like whacking the side of a TV), and the unit kicked on. Holy smokes...there seem to be no loose wires, so my thinking is the contactor is bad. I think I will replace it. Any other ideas? I don't have a magic touch.

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Jack wrote:

Sometimes they stick. But one that sticks is due for replacement.

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It sounds stuck. It happens, just replace it

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Likewise, we don't have a magical crystal ball.
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RBM wrote:

Not necessarily. Some modern electronic thermostats have short-cycle protection built in to their software.
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I should have said, it'll either click on immediately or in about five minutes

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My whole system is from 1979, not "modern" I would think.
Yet neither the heat nor the AC go on for 2 or 3 minutes after I turn it on at the thermostat, or at the power switch on the basement wall.
Is that the same short-cycle protection?
I have a Carrier AC and maybe a Carrier furnace too.
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For your own protection, back away from the unit, locate a phone and call a repairman!
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