Possible Causes

WARNING: This page is about a different car, the 2002 Mercury Villager. However, it is still accessible from the selected car via links, so may be relevant.

Battery Junction Box (BJB) fuse No. 26 (65-amp).
Central Junction Box (CJB) fuse No. 33 (20-amp).
Central Junction Box (CJB) fuse No. 39 (20-amp).
Ignition switch.
Blower motor relay.
EATC module.
Blower motor.
Blower motor speed control.
EATC module.
Open/Short circuit.