How Do I Test The Contactor In Ac Unit To See If It Is Bad?


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Old 07-11-06, 05:36 AM
K
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How Do I Test The Contactor In Ac Unit To See If It Is Bad?


Hi again all,

Have seen a lot of great questions and answers on ac in this forum. Could someone tell me how I can test out the contactor
in my unit. A friend at an elctric motor shop said to push it in
manually (earlier my unit came on for about an hour then outside fan shut down now it dosen't come on at all). Thanks.
 
  #2  
Old 07-11-06, 06:02 AM
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You can check voltages across L1 and L2, then Load1 and Load2 but that will only tell you voltages. If the contacts are burned it could allow voltage to pass but will not allow sufficient current to run the compressor/fan.

To check if it is mechanically operable, first check for 24v at the wires going to the coil of the contactor. The smaller plug on wires on the side, and usually lower than the high voltage wires. Your thermostat must be calling for the A/C to operate at this time and the breakers must be properly enguaged.

If you have 24v then you can easily plug them on and remove and replace one of them watching the contactor operate. It will have a definate clunk as it enguages and you can see it move.

If it does that then mechanically it operates. now, you just need to determine if your compressor/fan is operating correctly.
 
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Old 07-11-06, 06:26 AM
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Red face Thanks Mdtaylor

Will do exactly that tonight, again many thanks.
 
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Old 07-11-06, 01:31 PM
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If the contactor is not pulling in, and there isnt 24v present at the coil, then check for a manual reset pressure switch. If you press the button and the unit comes on, keep an eye on it for a while. High pressure switches will trip if the condenser fan motor is cutting off on overload. If you notice the fan spinning at a slow rate or making unusual noises, then you could need a new motor or (hopefully) just a capacitor.

If the contactor is pulled in and still nothing then check voltage. If there is not 240v present then check breakers and fuses.
 
  #5  
Old 07-11-06, 02:47 PM
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Will Do Servicemanager

Apreciate the follow up, hopefully by tomorrow night I'll have air.
 
 

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