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Re: a/c compressor hums
The compressor may be fine after setting off or a day. After retyring it then if it still dosnt start either replace the run capacitor to the compressor and fan motor or have it checked to see if it is in range.
The hum your hearing could that be the contactor relay humming?
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In the back of the compressor motor you will see a fan, remove the plastic cover to get to it..
Once you have the plastic cover removed and the fan exposed, plug the compressor in and spin the fan with your fingers...be quick as the fan could cut your fingers if you do not get them out of the way..
If the compressor starts working, then the start capacitor is bad on the compressor...if it does not run then you have motor troubles, either replace the motor or get it rewound.
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Please check if any rodents have snapped the wires to the ccompressor. You have not mentioned the make/ model/ type of the set. Whatever be the type the compressor must work on swtich on, If not check for the capacitor and the relay. You will need to trace from the control box. Also check if the mode is put to A/C and not fan alone. Check the supply line to the compressor and replace if the relay or capacitor is faulty other wise your compressor motor has failed if the voltage come to the compressor motor but does not work / no hum or noise. Please check this out. Good day
If the humming is your compressor running (feel the large copper line going into the unit, it should feel cold aftter a few minutes of run time) then the fan motor or the capacitor or both need to be replaced, check for voltage to the fan motor when the unit is "humming" if it has voltage and will not start replace the fan motor and the capacitor. hope this helps.
When you shut it off and back on it slugged the compressor if you turn it off and back on before the pressures equalize between the high and low sides it will slug the compressor and it will not run should let sit for five minutes or so before restarting. The humming is either the compressor making noise usually common for the compressor to make some noise or the fan motor bearings are getting bad on the outside unit. If the unit works normal probably not much you can do till it breaks if it is the compressor it is more economical to replace the whole unit if it is just the fan motor it is worth changing. You could take an amp draw on the fan motor and the compressor to see if the are within the limits on the name plate of the outside unit.
Sounds like you have either a bad fan motor or a bad fan motor capacitor. When you turn the unit on with the fan not working, the compressor (the humming noise) runs and gets real hot real quick resulting in the compressor cutting off ( the nothing after) on it's inside high temp switch. This is what the compressor is designed to do so that when this happens, it does not burn the compressor out. Replace you fan capacitor, give the compressor an hour to cool, then try it. In most cases and if I'm correct, the unit will run just like you want it to. Good luck.
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