I was just reading an article by Lynn Rademacher on EHow. This woman doesn't know the first thing about this unit. The blower motor resistor on a 1997 Pontiac Grand Prix is more or less a module which contains resistors (yes plural meaning more than one) to regulate the speed of the blower motor.
Depending on the speed settings in your car controlling the blower motor anywhere from 3 to 5 speeds are possible. On most Pontiac Grand Prixs (and I've owned a 1990, 2 1998's a 1996 and a 1997 and a couple of Oldsmobiles which work the same way) there are probably 5 settings. Each setting has a resistor regulating the speed of the motor except for the high setting which does not have a resistor associated with it. It's just full 12 volts to the motor. I've had a resistor module which was a printed circuit board and several that are an assembly of welded resistors. This type is much better as the printed circuit ones have a tendency to crack or in one case the resistor fell off due to possible over heating of the circuit. These were only soldered in place. Getting to the point of location; all these vehicles have the blower motor and resistor module located under the glove compartment on the passenger side of the vehicle. There is usually a grey felt covered panel made of fibrous material under the glove box that has to be removed in order to get to the blower motor and resistor module. First and foremost you have to be a contortionist to get to the screws holding the blower motor in (more than likely 3 screws. Use a 7/32 socket to remove) If you can reach and unplug the resistor module connector from the blower motor do that first. This is located at the back of the motor (GM designers really knew what they were doing here). The connector has a latch which is a pain in the you know what to undo. This is all done by feel as you cannot see what you are working on. If you have a little mirror so that you can see behind the motor may help. But once you put your hand back there forget the mirror. There is also a larger connector engaged to the resistor module. It's about an inch long and has several wires running to it. Disconnect that one first if you can. It is also "latched" so you have to relieve the latch before you can pull the connector out. If you were successful in disconnecting the connectors, remove the 3 screws holding the blower motor. It will drop down and may be a pain getting out as the area is quite cramped. There are also 3 screws (same socket size) holding the resistor module in. 2 on one side and 1 on the other. You only need to remove the one or ones in front that are easily accessible. The one or ones in the back only may need to be loosened or maybe not at all. The mounting positions for the module are slotted so the part can be removed by sliding it slightly forward and then down. Reverse the procedure for putting everything back together. Resistor module first. Replace the large connector there. Then the blower motor. The blower motor by the way will only align with the mounting holes one way so make sure you can see there alignment first before you put any screws back in. The rubber ring going around the perimeter of the motor housing should lock into the mounting bosses to ensure correct alignment. Also there is a short bent air hose which evidently cools the motor while it is running attached from the motor to the housing that the motor mounts to. Make sure this gets connected. Holding the motor in place while trying to get one screw in is also a pain in the ****. Replace the fiber cover (or not) with the 2 or 3 little push in plastic gizmos. Upon completing this task your sides and back will take a while to get back to normal. Good luck!!!
In addition to the description I just gave for finding and replacing a blower motor resistor and blower motor I wanted to add that if it still does not work and you know the resistor is good then the problem is in the ignition wiring harness that runs from the ignition switch down to the huge connector it plugs into. Don't ask me why cause I don't know. I've had this same problem twice and replacing this harness resolved the situation. It also resolves the problem of the automatic headlights that come on when you start the vehicle. I've had the blower motor switch turning off these lights depending on what position you had the blower motor fan regulated at. The first four setting turned off the headlights but they stayed on when the blower motor was on full blow. Turning on the headlight switch bypassed this problem.
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