Well, I have seen times that you needed to flush the lines if a compressor blew up and metal fragments were throughout the system or if the lines were left open for a long time,not plugged, and moisture etc would have collected. This is not the case here. However I agree that you don't need to flush the system every time. Anyway that doesn't solve the problem. Everyone with their suggestions and input has just about covered the entire system. There is something there that is obviously being overlooked. He may have to seek local professional advice.