Fan only works on 3

[cdnuser]

For some reason my fan only works on 3. 1,2,4 nothing, NADA.

What would cause this? Odd it works on one setting.

[Jigg]

There's a resistor in the controls somewhere that needs to be replaced... same thing happened to my girlfriend's exploder.

[HenryJ]

Low Blower Speed

When the Low blower (1) speed is selected, the HVAC control assembly applies voltage to the blower motor resistor assembly through the low blower motor control circuit. Low blower speed voltage will bypass the blower mode switch completely. Voltage is divided between 3 series resistors in the blower motor resistor assembly, to the blower motor relay on the blower motor supply voltage circuit, and the blower motor to achieve the desired blower speed. The blower motor is included in the series circuit by the blower motor supply voltage and ground circuits. The ground circuit provides a ground path for the blower motor.
Medium Blower Speeds

When the Medium 1 blower (2) speed is selected, the HVAC control assembly applies voltage to the blower motor resistor assembly through a portion of the low blower motor control circuit. The blower switch will direct the voltage through the medium 1 blower motor control circuit. Voltage is divided between 2 series resistors in the blower motor resistor assembly, to the blower motor relay on the blower motor supply voltage circuit, and the blower motor to achieve the desired blower speed. The blower motor is included in the series circuit by the blower motor supply voltage and ground circuits. The ground circuit provides a ground path for the blower motor.

When the Medium 2 blower (3) speed is selected, the HVAC control assembly applies voltage to the blower motor resistor assembly through a portion of the low blower motor control circuit. The blower switch will direct the voltage through the medium 2 blower motor control circuit. Voltage is divided by a single resistor in the blower motor resistor assembly, to the blower motor relay on the blower motor supply voltage circuit, and the blower motor to achieve the desired blower speed. The blower motor is included in the series circuit by the blower motor supply voltage and ground circuits. The ground circuit provides a ground path for the blower motor.
High Blower Speed

When the High blower (4) speed is selected, the HVAC control assembly applies voltage to the blower motor relay through a portion of the high blower motor control circuit. The blower switch will direct the voltage through the high blower motor control circuit. When the load side of the relay coil is energized, the blower motor is connected directly to battery voltage through the blower motor supply voltage circuit. The ground circuit provides a ground path for the blower motor.

First check the fuses. There are at least four located in both the dash and under the hood.

The resistor is located in the top of the HVAC housing under the hood. Make sure it is getting voltage first. Then you can use an ohmmeter to test continuity between terminals once disconnected. I have only seen a couple go bad in my experience, and never in an s-series. It is possible and a natural step in trouble shooting the problem.