It’s not the blower. It is the blower motor resistor pack that is designed to cut the voltage to the blower motor to control the fan speed. The resistor pack is by-passed on setting #4, so the blower motor gets a full 12V, running as fast as it can. Typically, these are located in the duct path close to the blower fan. The air running from the blower cools the resistors when running. Some of these packs are cheap, and some are expensive. They should have a 5-wire or 6-wire connector on it.