[BNaylor]

The ambient air temp sensor circuit is fairly easy to troubleshoot and check. At ignition to ON and climate control in AUTO, check for 4.5-5.5 volts DC at Pin A input (LT GRN/BLACK wire) at the sensor electrical connector. Pin B (Yellow wire) is ground. The way the sensor works is internal resistance decreases as temperature increases and vice versa. You can check the sensor out of the circuit with a digital multimeter. Plus you could use the one in your Regal as a calibration standard or comparison. If the sensor checks out then it is either a wiring problem back to the climate control head unit or the head unit itself.