Air Conditioner problems of the 2002 GMC T-series

There were several problems with my car. I purchased the car in June of 2004 at clay chevorlet in newton, MA. The first day I drove my car the temperature thermometer continued to flucuate between c and h. A few months later I was told that there was a problem with my demister and that was fixed. A few weeks ago I was told there was a problem with the fan and that was supposedly fixed. Recently the thermometer went all the way to h and did not cool down. My car was towed back to the company and I was told that something in the engine exploded and they are supposedly replacing the engine although I have been waiting for 3 weeks for it.