Don't sell quality

I bought a car a month ago. The aircon would blow cold air then hot after a few minutes. I thought it needed to be regassed . I took it to 3 places and was told its the compressor and the dealer would have picked it up if the done a diagnostic on the car. When I contacted them. They said there is nothing they can to as things like this happens. They not willing to assist in any way. SO THINK AGAIN IF YOU WANT TO BUY A CAR FROM THEM.