My in laws have an older hvac system. Last summer the compressor went out. They are an older couple who does not to try to make it thru this summer without air conditioning. I found a used compressor for 500$. They really don't have the money for a whole new unit, but we are going to figure out a way to do it if need be. Should I risk the used compressor? If they lose air again we'll just have to buy the new unit anyway. But if there's a chance a used 500$ compressor could possibly do the job then we will give it a try. I don't know how much used compressors usually go for, but I know if its too cheap it's going to be trouble.