Our 2002 Lexus SC 430 air conditioning system has a mind of it’s own. It blows hot air when it 90 degrees out side. I believe the system thinks it is 30 degrees and needs hot air. I have replaced the compressor, evaporator and the circuit board that controls all of the air conditioning modes and the system is still not operating properly. Has anyone had a similar problem or can suggest a solution?
Does it ever blow cold air? Did you check the compressor clutch relay?
Could it be the blend door or temp door motor is inop. Can you hear them driving when the modes are switched.
The problem might be with the expansion valve.
http://www.rockauto.com/catalog/moreinfo.php?pk=1003205&cc=1377817
The expansion valve is what meters the amount of refrigerant that enters the evaporaor as a gas. The disc on top of the expansion valve opens and closes the valve depending on the temperature inside the vehicle.
Tester