My AC began squealing one night so I cut it off and called the HVAC contractor that installed the unit and that services the unit each year (had just serviced it 30 days prior) When they turned the unit on it did not squeal but ran fine, the tech said it could the motor going out and to check, the next time it made the noise, to see if the fan was moving. The unit ran consistently for 4 days and then the squeal started and the fan was not running. I cut if off and waited and started it again the next day I woke up and it would not turn on. I replaced the motor and capacitor (the unit had a 60/5 440 capacitor, but when I ordered the motor they said it should take a 45/5 370 capacitor which they sent me. After installing the motor I decided to leave the old capacitor (wasn't sure if the new one was right) then turned on the breakers and the thermostate and noting... the inside blower comes on but the outside compressor and fan did nothing. The contactor clicks in, but nothing starts. So I don't know what to do... My unit does not have a fuse or separate breaker because it is next to the electrical panel. Is there a reset button or something else that I should try. Any help would appreciated.

The job of the capacitor is to give it a "kick" to get it moving. On the side of the motor itself it will say the correct capacitor for the motor. I'm sure they sent you the correct one with the new motor.

The motor probably won't work without a good capacitor, it will try and run and overheat the start windings inside the motor (the start winding are very thin strands of copper wire, and can be burnt-out very quickly if it is drawing excessive amperage, which happens with a bad/dead capacitor). The motors have an internal thermal switch which opens once hot (from trying and failing to start) and automatically closes once it cools down.

The voltage rating (330V vs. 440V) is not that important and are interchangeable for the most part. The capacitance rating is the important thing and can be tested with a good multi-meter (always shut power off to the unit before attempting anything!! ).
This value must be within 10% of the rating, so a 5MFD, or uF rating would have to read at least 4.5, and not more than 5.5. The small number is the Fan Capacitance and the large number is the compressor motor capacitance.

Try replacing the cap. With the once they sent you and make sure that you are getting 230V across both wires, on both sides of the contactor. A bad circuit breaker can give you two 110V legs to ground, but Zero or 440V across the two wires, in which case you would need to replace the breaker. Also check the contactor itself, when it is calling for cooling (the relay coil on the contactor should be "pulled-in" and making a connection. There should be no voltage drop across the contactor (a meter reading volts would read Zero going across the relay when "on").

Does the compressor attempt to run (either runs or give a quick hum and then stops? Again there is a thermal switch here as well. A quick hum is good and expected if you are still using the bad capacitor.

Thank you for your response. I did install the new cap that they sent with the motor and still nothing. There are no sounds coming from the unit at all. There is power going to it. At first the contactor would suck in when the power was turned on.. no it is in but there is nothing going on. Is there a way to reset the unit? I'm going to try and measure the voltage on the contactor.. Thanks again.. This value must be within 10% of the rating, so a 5MFD, or uF rating would have to read at least 4.5, and not more than 5.5. The small number is the Fan Capacitance and the large number is the compressor motor capacitance.

Try replacing the cap. With the once they sent you and make sure that you are getting 230V across both wires, on both sides of the contactor. A bad circuit breaker can give you two 110V legs to ground, but Zero or 440V across the two wires, in which case you would need to replace the breaker. Also check the contactor itself, when it is calling for cooling (the relay coil on the contactor should be "pulled-in" and making a connection. There should be no voltage drop across the contactor (a meter reading volts would read Zero going across the relay when "on").

Does the compressor attempt to run (either runs or give a quick hum and then stops? Again there is a thermal switch here as well. A quick hum is good and expected if you are still using the bad capacitor.[/QUOTE]

The contactor was the culprit this time... installed new one and now AC is working