Sounds to me like that is the Blower Motor Resistor. I had the same EXACT problem on my other vehicle ( 99 OLDS ) It is a little curcuit board that has several leads on it. One lead conrtrols one speed of the fan and such. Mine only worked on the last two high settings. And sure enough when I pull it out, all leads were broken except the last two. This is a known problem on my other vehicle and I had to replace it twice already in the last 5 years. Problem is, I having trouble finding a listing for this part on a 97. My suggestion would be to research the Blower motor resistor. Feel free to email if you have any questions.
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