Sounds like the temperature contol wheel is broken. I repaired mine about 4 years ago and did a post on it. It can be repaired with a drop of solder if I remember correctly. I also seem to remember that if I turned the wheel to full hot, then the heat would activate... then you can controll the heat by adjusting the fan manually.

Anyway thats a start for you.

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Earl



1993 190E 2.3
2000 Toyota 4x4 Tundra