I attempted to start my air conditioner the other day with no luck. The unit ran fine right up to the end of last summer with no problems. I set the thermostat to cool and lowered the setting below the temperature in the house so the unit would turn on. The furnace blower turned on but the outside unit did not. Neither the compressor nor the outside fan were working. There was also a humming noise coming from the contactor. I tried several things after reading answers from other peoples questions. I tried spinning the fan to see if it would start with no luck. The fan turned freely and was not restricted. I changed the capacitor and this did not help. After I changed it though, the humming noise went away. The contactor seems to be working. I put a meter on it and I'm reading 123v on both contacts going in and coming out of the contactor. I also read that its possible a high pressure switch might have shut the compressor down if the fan wasn't running and the compressor was. Where would the reset button be located if it has one? Does the outside fan not run if the compressor is not working? There is power going to the fan motor, and it spins freely so I don't think there is a problem with it. Should I try changing the contactor even though I have power going to the compressor and the fan? If I do change the contactor and it still doesn't work, does this mean the compressor is bad? :confused:

See that you have 240 Volts out from contactor, You may have a bad contact on contactor.

did u say 123 volts at each contact,, 123x2 total 246 or there abouts if you check both contacts at same time,, or is the total of both together 123 volts

I agree with wmproop. You need to check voltage on the contactor from each power leg at the same time(240v). You can have power on one side checking to ground(120v) and it will show up on the other side showing the same from reading through the windings of the motors.You may have lost one leg of power.

If a contact is open on on half of contactor, you may read the same 123 volts(same leg).
123 volts is a little important, 240 Volts present is Very Important.

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Originally Posted by LBI08

I attempted to start my air conditioner the other day with no luck. The unit ran fine right up to the end of last summer with no problems. I set the thermostat to cool and lowered the setting below the temperature in the house so the unit would turn on. The furnace blower turned on but the outside unit did not. Neither the compressor nor the outside fan were working. There was also a humming noise coming from the contactor. I tried several things after reading answers from other peoples questions. I tried spinning the fan to see if it would start with no luck. The fan turned freely and was not restricted. I changed the capacitor and this did not help. After I changed it though, the humming noise went away. The contactor seems to be working. I put a meter on it and I'm reading 123v on both contacts going in and coming out of the contactor. I also read that its possible a high pressure switch might have shut the compressor down if the fan wasn't running and the compressor was. Where would the reset button be located if it has one? Does the outside fan not run if the compressor is not working? There is power going to the fan motor, and it spins freely so I don't think there is a problem with it. Should I try changing the contactor even though I have power going to the compressor and the fan? If I do change the contactor and it still doesn't work, does this mean the compressor is bad? :confused:

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I checked each contact separately and got 123 volts at each.

You NEED 240 Volts Out of Contactor.
I should have said 123 Volts is not important at all, With contactor energized you need 240 volts on line side, and 240 volts on load side.