Central Air Conditioner problems?

Last July I started noticing that my outside unit got louder. At first I just thought that the casing was loose, and if I applied a little weight to the outside case the noise would go away. About a month later (August) cold air stopped coming out of the vents. I called an A/C repairman and he told me to just shut it off and just run the fan for about 4 hours to defrost the outside line. It worked and we had our A/C back, for a little while. Afew weeks later the unit did it again. Next problem is when we go to turn the unit off, the outside fan isn't shutting off. We had to shut it off via circuit breaker. I was told It's a bad contactor causing this. So my question is, could the bad contactor also be the reason why cold air wasn't coming out? the reason why the outside pipes froze?