You have a burned out resistor block which is mounted to the heater air flow box. If you open the glove box and push the release tabs on the side you can the lower the door a little bit more to see the base of the heater box. The resistor is a white rectangle about 1.5 by 2.5 inches long with a 3 prong plug ( toward the hump of the car).
Use a phillips and remove the block and you will notice that the ceramic is all dry and cracked with a slight burn smell I have replaced mine twice so far. Once at 40k and once at73k and so far so good.
I hope this helps
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