OK, I'm struggling with this problem and y'all might be able to help. I have posted to alt.hvac, but most of those guys are really not very helpful to homeowners and just tell me to call a tech, and this is a DIY forum so bear with me.
background:
AC quit working, would cut-out after startup. Thermostat was changed no result. Called Tech, who tested everything, put 2lbs of r-22 in it, indicated the condenser fan motor was giving trouble starting and that likely it had some bad windings or something. Cutting out was b/ c the fan was not working and the compressor would hit the overheat limit and cut out. He tried changing the capacitor, no improvement. Wrote an estimate for changing the motor out of over $500. Being thrifty and handy enough to be dangerous, I decided this was too much for something I could do myself.
I looked around and after getting the details on what the motor type was, I found a OEM replacement at Grainger. 1/4 horse, 220 volt, Y frame, counter clockwise rotation, sealed air-over, bottom shaft, etc. I got the motor changed out, substituted the new 12mfd capacitor that this motor required (vs the 5 mfd for the other). I took pains to connect the wires back just as it was before. The new motor had the same colors leads as the old one, a purple, a brown and a black.
As I tested it, I discovered that this motor does not want to start either, in fact it makes the same loud humming noise when energized. When I spun the motor with a stick through the grill and it caught on and ran normally. Hmm.... The compressor runs strong and has no issues.
After looking at the way it had been wired when I opened the case, their are two hot 220 leads and the case is ground. Going from either lead to ground is 115 volts. Obviously between the two leads is
220-250 volts.Of these two hots, one BLACK HOT wire goes to the contactor (relay) switch and then would connect to the purple fan motor wire when energized.
The WHITE HOT connects to a wire that goes to a 3 way capacitor (runs the compressor), with a jumper directly from the input terminal sending power also to the condenser fan motor capacitor.
The other two condenser fan motor leads, the brown and black, are connected to the starting capacitor, one on one side and one on the other. The black is connected to the same terminal as the hot lead.