I have an 02 Impala. The heater does not warm up and blow heated air. The fan works. The Temp gauge appears to work, although the temp fluctuates temperatures between about 180-220, first rising then dropping back. It never rises to the point of overheating though. The fuse for the ac system appears to be intact. I suspect the thermostat but am unsure since the temp gauge runs within the normal range...???