Where do I need to start on checking things out on my 83 300sd, The ac has been working ok, most of the time it blows medium cold to really cold, but from time to time it would not blow at all and I would have to press the defrost button to get it to blow, after I did that it would blow fine. Yesterday when I got in the car and turned it on, it would not blow at all, in fact when I am going down the highway it blows heat out of the vents under the dash??? And the blower still does not blow even when I put it in defrost. Any ideas at all? Thanks, Hudson