If you want to check the evap temp sensor, try this. With the engine running and the ACC temperature set to LO (fan speed two or three), press and hold the REST button until the display changes. Then repeatedly press the left side AUTO button until the left side of the display reads 05. The right side will then display the evaporator temperature (as reported by the sensor). If it's too low the compressor won't engage, same thing if it's implausible. One word of caution though. Sometimes the reading will be in Celsius, sometimes Farenheit.