It sounds like there may be an issue with the blower resistor or the heater fan switch, preventing the blower motor from running at lower speeds. I've attached a diagnostic chart, below, that can help you test both of these components to see which one may be faulty. I've also attached photos and diagrams showing the locations of the blower resistor, heater fan switch, and blower motor relays.
Additionally, these repair guides explain how to check the wiring in a vehicle, and how to use a test light:
Please let us know if this helps!
Thanks, Wendy W.
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Friday, April 8th, 2022 AT 6:51 AM