What's wrong with a central air conditioner unit when it keeps dimming the lights in the house on and off and blows warm air out of the vents?

The lights dimming are a sign that it's drawing too much electricity in relation to the amount of electricity that's being supplied to your house overall.

The compressor trying to start is drawing too much current. It could be that the compressor is locked up. It could also have a bad start or run capacitor.