This 2001 Pontiac Grand Am came in with the complaint that the low and medium 1 blower speeds do not work. Since the higher blower speeds work fine, the diagnosis will begin with the blower resistor assembly.
The blower resistor is under the passenger side of the dash.
The lower dash hush panel needs to be removed.
A couple of 7 mm headed screws.
A push pin.
The outer underdash cover comes out.
Next the inner cover and duct assembly.
Since the blower was working on the higher speeds, testing is as follows.
Blower switch set to low. There should be battery power on the yellow wire.
Blower switch set to medium 1. There should be battery power on the tan wire.
Blower switch set to medium 2. There should be battery power on the light blue wire.
Blower switch set to medium 3. There should be power on the purple wire.
Blower switch set to high. This signal is sent on an orange wire to the blower relay in the underhood fuse box.
If the signal is sent and the relay and remaining wiring is working correctly, the blower motor will work. Assuming of course that the motor itself is good and the is a proper ground at the black wire, terminal “A” of the blower motor connector. High blower power is delivered on the purple blower motor wire, terminal “B”via the blower relay normally open contacts.
The dark blue wire at the blower resistor goes to the normally closed contacts in the blower relay in the underhood fuse box and then on to the purple wire at the blower motor. All of the lower blower speed signals go from the blower switch, through a resistor or up to a total of all four resistors before going to the normally closed contacts in the blower relay. The signal finally arrives at the blower motor on the purple wire.
If the blower motor does not work at all testing should start at the blower motor and be done with all harnesses connected.
There are two screws with 5.5 mm heads that hod the resistor in place.
The old design resistor with a short green circuit board.
The new design longer blower resistor with a black circuit board.
I reassembled this one and gave it back to the customer.