Focus ZX3 2.0L ZETEC

• Automatic transmission
• 55,000 miles

After having the car for about a year, in the summer of 2006 I was driving and felt a quick jump, then my car started shaking. I didn't pay much attention to it thinking it was the music. The next day I got in and turned the air on and the car started to shake really badly. I opened the hood and saw it was the fan shaking, shut off the car, turned down the air knob, turned it back on and it stopped. I went the summer w/o A/C. I was showing a friend one day and it didn't do it, thought the problem had stopped, but when I pushed the A/C button it shook. Also when I put the front defrost on it shook as well. At one point I was sitting in a parking lot with the car on, the fan shook then sounded like it was breaking, sure enough I turned everything off, turned on, pulled forward and parts of my fan blade were under my car. As of now it will still blow out hot air, "cool" air (doesn't help in Texas heat), and the defroster will run but will cause massive vibrations in the engine bay causing the whole car to shake. It also will randomly start shaking if the car is in heavy traffic.
On a side note I had traded the car in to a dealership but had some problems with the financing and one salesmans ignorance so I had to take the car back. I'm not sure if this problem originated from them or not as it happened about 3 days after getting the car back in the middle of the day. I expect its a defect though.