When a car blower fan doesn't work, the problem could be with the fuse, the fan relay, the blower resistor or the fan motor itself. To check the fuse, use a multimeter to check both ends of the fuse for power. If there is power on one end of the fuse but not the other, replace the fuse.
To check the fan relay, touch the relay or listen to it while switching the fan's control on and off. If you feel or hear clicking, it's an indication that the fan relay is functioning normally. If not, replace the relay.
To check the fan motor assembly, use a multimeter to check the motor for power. If there's power at the fan's terminals but the fan is not working, the blower fan is defective and needs to be replaced. If power is not present, there could be connection problems in the internal wires. Take the motor to a certified auto electrician for repairs.
If the fan operates at one or some speed settings only, the blower resistor is the cause of the problem and should be replaced. Locate the blower resistor, detach it, and bring it to a parts specialist for replacement. A car's blower resistor is often located near the blower fan motor. If you cannot locate the resistor, consult the owner's manual.