To add to what Gilly said. I would be wondering if the aspirator motor is working. This little motor draws air across the inside temp sensor which would give the same affect as a bad sensor if it is not working. I quick simple test is to take a small piece of paper and see if, with the key on, it will stay stuck to the grill on the sensor. A dirty sensor will react slow to temp changes too. The sensor is located next to the sunroof switch. The motor is located to under the right outside dash vent.

fasthair