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We have a 1997 Chevy Suburban. During the winter we were in Utah and our front blower motor started shrieking like a banshee, so we replaced it (it was very, very cold outside so not blowing hot was a problem. Also it was a cold job replacing it).

However, after we replaced it it seems as though the fan has two speeds: High, and off. Specifically it doesn't matter where on the dial we turn it, if it's not at high it's not blowing.

Why would it be doing that, and how can I fix it? The motor that I bought is a "premium quality blower motor" by Murray climate control. Model PM149, I think?

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Check the blower motor resistor. When it goes bad it defaults to high speed. The resistor is usually near the blower motor.

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    Some cars will default to high speed, others won't work except when turned all the way up to high. – GdD Jun 28 '17 at 7:45
  • Blower motor resistor was it. $23 later, some seriously scraped knuckles (There is a special place in hell reserved for auto manufacturers that design parts for easy removal when the car is missing a windshield and dashboard), and I've got speed control, woo woo! – Wayne Werner Jun 28 '17 at 18:12
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The resistor is a big (often 20mm square and 75mm long) ceramic core with various sized nichrome wires wrapped around it. All of the speeds (apart from off and high) are derived from combinations of the resistances of these windings. Fortunately, you can rewind the blown winding with an identical thickness nichrome wire of the same number of turns. Any slight variation in thickness and length shouldn't alter the motor speed drastically. Or simply go to a wrecking yard and buy a replacement resistor for your year and model Chevy.

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    You can get brand new replacements for $20, I'd suggest buying one of those. – GdD Jun 28 '17 at 7:44
  • Looks like it wasn't a blown winding but a capacitor or resistor or something. At least the windings all look fine. – Wayne Werner Jun 28 '17 at 18:13

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