Why do I have excessive RPMs while driving, but the transmission is shifting normally?
Heater blower burnt out for a second time. Is this common?
This can be common for a 17 year old truck for sure. Also the after market blower motor will not be the same quality and won’t last near as long as the original motor.
If the blower motor only works on high speed or certain speeds the motor itself may be just fine. The problem would be with a faulty blower motor resistor.
HVAC Blower Controls Circuit Description
Battery voltage is supplied to the blower motor resistor relay assembly connector at all times. When the ignition switch is OFF or the blower switch is in any position except HI, no voltage is applied to the relay coil via blower high speed and the relay remains de-energized.
With the blower switch in HI, the blower resistors are bypassed and voltage is supplied to the coil side of the permanently grounded relay. This closes the contacts and supplies full battery voltage from the engine wiring harness junction block to the blower motor which will operate at the highest speed.
When the blower switch is in LO to any MEDIUM speed, voltage is reduced through the appropriate resistors which will limit the blower speed accordingly.
The blower motor resistor relay assembly is located next to blower motor under right side of glove compartment (Pickup) or at the right rear module assembly (Utilities w/auxiliary A/C).