The house was not cooling. The furnace in the basement was blowing, so I went outside to check the condenser unit. It was humming and the fan was not turning. The outside unit is clean, I have taken it apart and vacuumed all the fins this spring. I suspect it could be a relay that has gone out or something similar. How and what do I check to get the fan working again? My experience is in large appliance repair and also some in major auto repair (fuel pump replacement). Thanks

Check the circuit breakers and fuses for the outside unit. See if that helps and post back.

Check the circuit breakers and fuses for the outside unit. See if that helps and post back.
Thanks for the quick response. I know that there are circuit breakers, so I don't know where I would look for any fuses for the unit. The unit was humming, not the good type of electric hum, so I assume that there is power there. Without getting physically into it, I am thinking the compressor, fan, or some kind of relay, etc has burnt out?? Could that be a possibility? Is there a list of testing steps that I could perform to troubleshoot? Again, electric hum but the fan was not turning.

Look inside your outdoor disconnect that is near your outside A/C condensing unit. There might be fuses in there. Test the fuses and make sure you have 220 Volts before you go any further.

The house was not cooling. The furnace in the basement was blowing, so I went outside to check the condenser unit. It was humming and the fan was not turning. The outside unit is clean, I have taken it apart and vacuumed all the fins this spring. I suspect it could be a relay that has gone out or something similar. How and what do I check to get the fan working again? My experience is in large appliance repair and also some in major auto repair (fuel pump replacement). Thanks
Check for line-voltage power supply at line-side of contactor-you may have a blown fuse or tripped breaker. Also check capacitor at outdoor unit-does the terminal end appear swollen or is fluid leaking? Replace if so.

Does the top of the unit seem warmer than it should? I there any smell of electrical burning? My unit had the same symptoms and it was he fan motor. It I spun the blade, it would start turning by itself but on shut down, it would not start by itself again. Either the motor is going up or I was told that there is some kind of starter thing that needed replacing.

Look inside your outdoor disconnect that is near your outside A/C condensing unit. There might be fuses in there. Test the fuses and make sure you have 220 Volts before you go any further.

Didn't have time to get back to last week. I replaced the fuses and still the same symptoms.
Will look into other suggestions that have been posted. Thanks.

There may be a phase missing since it is 220 vac.. Check the relay that

Provides power to it... Make sure 220 vac going to motor...

Usually a motor humms because it is stopped, use something like a stick to try

And get it spinning, if it takes off with help the capacitor is probably bad... if it

Doesn't turn get the motor tested it is probably bad... If you replace the motor

It might be good idea to replace capacitor it works 3 hot months in a year,

And sits around idle in the winter and freezes... If it fails, could burn out motor

Like already stated if it is your motor definitely replace the capacitor just make sure the ratings are the same.

There may be a phase missing since it is 220 vac..Check the relay that

provides power to it...Make sure 220 vac going to motor...

Usually a motor humms because it is stoped, use something like a stick to try

and get it spinning, if it takes off with help the capacitor is probably bad... if it

doesn't turn get the motor tested it is probably bad... If you replace the motor

it might be good idea to replace capacitor it works 3 hot months in a year,

and sits around idle in the winter and freezes...If it fails, could burn out motor

Thanks! You guys are great. Sorry it takes me so long to respond. (3 kids you know)
Anyway, I took the fan and motor with the condenser to a friend (works in Commercial Heating and Cooling) to have them checked out properly. They checked out fine. So he is coming over tonight to check out the compressor. I told him the sound (low hum) and he is pretty sure it is that. Will keep you posted. Thanks for all the great help. You have no idea how much I appreciate it. I will keep you posted.

Like already stated if it is your motor definetly replace the capacitor just make sure the ratings are the same.

Thanks! You guys are great. I am learning a lot from this whole experience. Sorry I am slow to respond.
Anyway, I took the fan and motor with the condenser to a friend (works in Commercial Heating and Cooling) to have them checked out properly. They checked out fine. So he is coming over tonight to check out the compressor. I told him the sound (low hum) and he is pretty sure it is that. Will also check out the electrical with his help. Will keep you posted. Thanks for all the great help. You have no idea how much I appreciate it.

Most modern residential condensing units are equipped with a dual capacitor (serves both the compressor and the fan motor). If it fails, neither component will function and a hum is usually brief but noticeable as the compressor attempts to start, then the internal overload opens. I have encountered partial failures that allow the fan to run, giving the appearance of a unit that is working. If you have 240 volts present at load-side of contactor but compressor and fan are not running, the capacitor is a very likely culprit. If it is leaking fluid and/or appears swollen/bulged on one or both ends (like a frozen pop can), that is an obvious sign of failure.