Nissan Repair: ac repair, nissan quest, ac repair

Question
I have a 1999 nissan quest van and the front ac will not blow cold air.  I have already check the gas and it ok but still not get cold.  The rear unit blows cold air but the front unit will not.  On the control panel I can only set the rear unit on 3 if i set on anything else it will cut off.  I don't know if it the control panel or what.  Can you please help me

Answer
Bernard,

You have the automatic control unit and if you put together that the front does not blow cold air and that the back only blows cold on 3 would lead me to the control panel.  If it was only the front I would say a blend door has failed.  

http://www.tomorrowstechnician.com/Content/Site301/SmartProducts/NissanInfinitiC...

The aforementioned kind of gives you an idea of how the system works.  If there is a door that is not opening, under the dash, that can cause the air not to blow cold.  But, for the blower in the rear only to work on 3 means the computer board is defective or the blower resistors are failing.  But, the resistor should only work on 4 and not 3 so again I say it is probably the computer.