F150 2004 blower working only on high position.

This is because your blower motor resisters are burned out for speeds 1,2 & 3. High speed does not have a resister.

Replace the resister. If it goes a 2nd time, it is because your blower motor is failing & drawing too much current.

it is behind the glove box I think. It is in the plenum case where air blowing on it keeps it cool.

Easy repair. May need to access throught glove box which should open all the way down when you squeeze the sides in.

Go to tascafordparts.com for a discounted resister.
Please rate as solved problem if this is what you needed.

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Manual Climate Control System Outputs
Blower Motor Switch Resistor
Blower Motor Resistor Coils Blower Motor Thermal LimitF150 2004 blower working only on high position. - 47afe58.gifsrc="/uploads/images/47afe58.gif" alt="47afe58.gif" class="h_mi" /> The heater blower motor switch resistor has the following features:

• The assembly is located on the passenger side of the plenum assembly behind the glove compartment (06010).
• Three resistance elements are mounted on the resistor board to provide four A/C blower motor speeds.
• Depending on the heater blower motor switch position, series resistance is added or bypassed in the A/C blower motor circuit to decrease or increase A/C blower motor speed.
• An overheating protective device (thermal limiter) will open the resistor coil circuit when the temperature reaches 121°C (250°F), interrupting the blower motor operation in all speeds except HI.
• The thermal limiter cannot be reset and is not serviceable.

Call your local Ford dealer parts department and explain your problem.  Ask them for a base part number 19A706 resistor and the location so you can replace it.  This part is located in the heater plenium chamber under the dash.  This should reactivate your fan speeds to normal.  You might also want to check the electrical conection to the resistor, as it has been known to melt from high heat at the connection.  That part, if needed is 14S411.  The numbers I've stated are base numbers.  Your local Ford parts guy will do the rest.