If the heater fan on your 2002 Ford Focus isn't functioning, or will only run on one speed, you may need a new heater fan resistor. This is an easy task for the do-it-yourself mechanic, because the heater box doesn't need to be removed to gain access to the fan or resistor. Before attempting this repair, properly diagnose the problem to eliminate other potential points of failure. It's easier than replacing parts that aren't bad, and cheaper!
Remove the passenger footwell lower trim panel underneath the glove box.
Open the glove box and remove the screw holding the footwell air vent duct. Pull off the hose and remove the duct. Close the glove box.
Disconnect the heater fan electrical connector. Remove the three bolts retaining the heater fan and remove the fan.
Disconnect the heater fan resistor electrical connector, and remove the resistor.
Install the new heater fan resistor by reversing the above steps.
Vacuum out the heater fan assembly to remove any debris that may have collected. Water intrusion into the heater box, causing heater fan and/or resistor failure, is not uncommon on these vehicles. Check for signs of water, and perform the necessary repair if necessary to prevent future problems.