my central air conditioner unit ( outside) does not work.. .. When i apply power to the unit the fan does not turn on but the unit makes a buzzing sound every 15 seconds or so .. it sounds like it wants to start but cannot .. if i stand beside the unit, the fan does not turn but every 10-20 seconds i here a buzzing sound and then it quits

-- can you tell me what could be wrong with the unit and identify what part(s) will need to be replaced

or can you tell me what trouble shooting tips you can give to identify what part is needed

thanks

If you unit has a dual capacitor (one for the fan and compressor it could be the problem. You can spend a lot of $$ by guessing what is wrong and replacing parts that are not bad. There are many things that can cause this problem but not limited to blown fuse/breaker, defective capacitor/fan motor/compressor/lack of 24 volts from the inside unit to activate the the contactor in the outside unit. Also if there are low or high pressure controls in the outside unit this could also cause this problem.

It could also be a burnt wire on the contactor or other areas of the unit.

need more info on your unit , is it a heat pump outdoor unit ? , if so it could be a bad defrost board , which has a compressor time delay built in and i have seen this device fail in the exact same manner , as described by the consistant time 10-20 seconds , and buzzing indicates low voltage to contactor coil is inconsistant as the defrost board supplies voltage to the contactor . also could be bad contacts on board fan relay causing fan not to operate and unit shutting down on high pressure switch .

This post is very old. Please read the date before posting.

Good observations on your part. Classic symptom of a failed capacitor. If it appears swollen or is leaking fluid, replace it.