Climate control problem - help

[raywcleung]

Hi - I don't know if this has been posted before. When turn the climate control knob to medium cold in hot summer, it will normal cooling for some time, but suddenly the outside temperature display was black out and air vent start to blow hot air instead of cold air, when I turn the temperature knob to max cold position, the cold air come back - the outside temp display come back. But it just happend once a month. I am not too sure if I need repair my car or take to dealer, can anyone help.?
Thanks - Ray