I have an ducane condenser unit. and every time i turn my ac on the unit will run well for about 20 minutes to 30 minutes and then the unit fan stops but the compresser still run and humms. so i shut the unit down for 1/2 hour or so and start the unit back up and it does the same thing run for awhile and stops. can you help.

In all likelyness it's either the capacitor for that fan motor or the motor itself. When the motor is replaced, the cap is too.

Dual caps are common and sometimes a single cap is used for the bad one or replacement fan because the size s different.

Two simple tests:

1. When it as no possibility of turning on, check the friction, Let it stop check the friction. If excessive replace fan and cap. Pulling the blade can be difficult without the proper tools. You need to be sure you get the right direction of rotation.

2. Next test is more difficult, so i won't mention it yet.

Sounds like heat is building up and causing a failure. Since capacitors are usually cheaper and easier to replace than motors, and you may want to replace it anyway, I am tempted to start there.

But just to rule out the motor try Keep's suggestion to check the motor. Also, try checking for excessive end play or slop in the motor shaft by: cutting power to the unit, open the access panel and reaching up to the fan and jiggling the shaft.

My second test, basically involves spinning the fan backwards and engaging the contactor manually and seeing if the fan reverses itself. Lots of potential for cut fingers, sparks etc.