The evaporator has a temperature sensor on the driver's side by the accelerator pedal. Tech's may give a clue how to test it! Also, do you see water coming out from the bottom of the car, as in the drainage tubing working properly. Also, the inside temperature sensor may be acting up or the pump that "sucks" air through a small screen on your overhead lights may not be working (sucking air). An easy way to check this pump if it is sucking air is, get an smoke producing "agent" and see if the smoke is sucked into that screen.