The blower motor on your Previa rotates a fan when the heat's turned on to circulate warm air from the heater core. As the motor ages, it eventually wears down and starts to malfunction, or stops working altogether. Low air circulation from the vents within the cabin is typically one of the first signs of damage to the blower motor. Other symptoms include the blower only working on one setting and loud clattering when it’s turned on.
Open the empty egg carton and with a black marker write the following above five of the empty egg pockets: "coolant reservoir nuts," "power steering bolts," "heater unit nuts," "lower cover bolts" and "blower mounting bolts." Every time you remove any bolts, place them in their corresponding location in the egg carton.
Remove the negative cable from the battery. Remove the two bolts holding your coolant overflow bottle on the side of the heater unit. Push the overflow bottle to the right slightly; the bottle itself doesn’t have to be removed.
Remove the two bolts that connect the upper and lower heater box near the power steering reservoir. The reservoir does not have to be removed either.
Remove the control cable on the right side of the heater unit by hand. All you have to do is pop the cable off its connecting tab. This cable controls where the heat blows from within the van—for example the defrost setting, or floor settings on the dashboard.
Remove the four nuts on the left side of the heater unit connecting it to the firewall. Remove the four nuts on the right side as well.
Pull the top portion of the heater unit toward you and remove it from the engine compartment.
Disconnect the two wiring harness plugs leading from the lower portion of the heater unit. Both harness plugs have safety clips that have to be depressed. If you can’t depress them by hand, use a flathead screwdriver to push down on the clips while unplugging each of the plugs.
Remove the four lower cover bolts from the heater unit and then carefully remove the entire lower heater unit from the van. Unplug the wiring harness connected to the side of the blower motor.
Remove the rubber cooling tube connected to the blower motor by pinching it between two fingers. Pop it out of the side of the motor.
Remove the four mounting bolts securing the blower motor. Extract the blower motor from its housing on the unit.
Install the new blower motor by reversing the removal steps precisely. Check the blower motor on all of its circulation settings to make sure it functions correctly.