A series of resistors controls the speed of your Expedition's blower. At high speed, resistors are bypassed and a full 12.6 volts are sent directly to the blower motor. At lower speeds -- medium 2, medium 1 and low -- the voltage is dropped accordingly across the resistors. If the blower isn't working at all - even on high -- then chances are the blower motor has failed. There are some tests to run, to make sure the problem doesn't lie in the blower motor circuit or in the control panel itself. The following procedures are based on a 2011 Expedition, however, other years are similar.
Pull outward on the junction box cover that is located on the far passenger kick panel. Look upward at the sound insulator under the dash on the passenger side. Remove the two push-pin retainers just below the glove box.
Use a flat-head screwdriver, or trim removal tool, to gently pry the retainers out of the insulator panel.
Pull the insulator downward from the front, then pull it toward the rear of the vehicle to remove it. The blower motor is in the bottom of the HVAC case secured with three bolts.
Locate the wiring harness on the blower motor. Squeeze the locking tab with your thumb and index finger, then pull the connector out of the plug on the blower motor.
The following step requires introducing live voltage to the blower motor. To prevent serious injury and electrocution, do not touch your power lead to any metal, and do not cross your power and ground leads.
Connect one of your test leads to the positive battery terminal. Connect it to the blower motor by sliding the female blade connector onto one of the connector blades on the blower motor. Pull back the carpet a little bit to expose one of the body grounds. Remove the bolt, using a socket at ratchet, then add your negative test lead to the body ground. Snug the ground bolt. Touch the female blade connector to the other blade on the blower motor plug. If the blower motor turns on, the blower motor is good. If the blower motor doesn't turn on, follow the next section to replace the blower motor. If the blower motor operates correctly, proceed to the section titled "Testing Blower Circuit."
Remove the three bolts that secure the blower motor with a 10 mm socket and a ratchet. Rotate the blower motor until the vent opening is facing the rear of the vehicle.
The dash panel trim has to be deflected just a little bit to allow the blower motor past the heater core and evaporator core housing. Do not deflect the trim more than absolutely necessary, or it will break causing damage to your vehicle and the potential for personal injury.
Depress the ridges in the dash panel insulator just enough to gain clearance, then lower the blower motor out of the case.
Pull the carpet back to help provide more clearance for blower motor removal.
If the replacement blower motor didn't come with a new wheel, pull the small e-clip on the tip of the blower motor shaft with a pair of pliers, then slide the wheel off of the old blower motor. Transfer the wheel to the new blower, if needed, then install the e-clip.
Lift the new blower into position, then turn it so that the vent tube faces the original direction. Install the mounting bolts and snug them. Connect the wiring harness and verify correct operation of the blower.
Follow Step No. 1 from the section titled "Accessing the blower motor" before performing this procedure.
Disconnect the wiring harness from the blower motor. Review the wiring diagram for your specific vehicle and determine which wire is the ground wire, and which is the power supply wire. Plug the positive lead of a volt meter into the power supply terminal in the harness, then plug the negative lead into the other terminal. Set the volt meter to DC current on the 20-volt scale. Turn the ignition key on and turn the blower speed knob from from low all the way to high. Voltage should range anywhere from 3 to 5 volts on low and increase proportionately to 12.6 volts on high. If you only get voltage on the high setting, or only when set to certain speeds, check the wiring between the resistor and the motor. If the wiring looks good, replace the blower resistor. If you don't get any voltage -- even when the blower is set to high -- but the blower motor worked when hooked to direct power, check the blower motor fuse. If the fuse is good and has power, replace the blower motor relay.
Disconnect the wiring harness from the blower motor resistor. Review the wiring diagram for your specific vehicle and determine which wires provide power from the control panel to the resistor. Check for voltage on on this wire. If there is voltage to the blower, but you didn't see stepped voltage during step one, inspect the resistor plug for corrosion and damage. If the plug is in good condition, replace the resistor. If you don't get 12 volts on the power supply wire, suspect the wire between the control panel and the blower, or the control panel itself.
Pull outward on the lower, center dash finish panel to disengage the retaining clips, then set it aside. Gently pull outward on the upper, center finish panel to disengage the retaining clips.
If the clips don't want to disengage with a light tug, wrap some masking tape around the tip of a flat-head screwdriver, and gently pry around the edges of the finish panel to disengage them.
Pull the panel out from the dash, and disconnect all connectors except for the control panel connectors. Review the wiring diagram, and determine which wires supply power to the resistor for low, medium and high speeds. Probe each wire to ground while the speed selector is on the respective setting. If there is no power from the control panel, replace the panel. If there is power from the control panel, but not at the blower, inspect the wiring for the between the control panel and the blower and repair as needed.
To replace the control panel, start by disconnecting the wiring harness. Once the harness is disconnected, remove the four retaining screws to separate the control panel from the center finish panel. Install the new control panel and snug the screws.
