Condenser fan shakes when A/C is on. Can the fan be tightened and how?

Depends on the cause of the looseness. If the center hole in the fan blade is wobbled out, you can try filling the gap with a semi-hard gasket sealer in a tube and letting that set overnight. Epoxy would work too, but then you're committed to a bigger repair bill if the motor ever fails. Chrysler has two sealants I'm very familiar with. One's black and one's gray. The gray stuff gets harder and would be the better choice for this type of repair. There are a lot of good similar products out there but I don't use them so I can't tell you which ones to use.

It's equally likely the motor has a bad bearing or bushing. There isn't anything you're going to do for a permanent fix other than to replace it. Sometimes if you can sneak some grease or oil into the front one it will quiet it up for a little while but that will only last long enough for you to verify that's the cause of the noise.