I'm really surprised NO ONE picked up on the fact that you said the car vibrated at the light when your fans come on regardless of A/C operation... hello... guys, it's a gimme.
The fans come on automatically to help the condensor do its job but as soon as you said it didn't matter if the AC was on and you clearly stated your problem that as the fans come on the car shakes like heck, well, obviously its the fans.
You could have either unpluged the AC via fuse, and turned on the AC to trigger the fans and watched the one fan wobble dobble all over and saved yourself some coin.
600 bucks, man I need to up my fee for side jobs. Slipping fans and the shroud in is an easy task.