Check fuses obviously then theres a thick purple and black i think wires that go to the heater fan its self up under the passangers side habe to remove the cover under the glove box if its still there
nearly ever one ive seen has been black burnt and chared give them a clean
If the fan works on some but not all speeds the fan resister relay under the plastic tray under the wipers is faulty
Wipers off and plastic cover dont lever against the windscreen to lift the metal clips ends badly ask me how i know
Then in the middle there is a white plastic dome with 2 screws the resiter is in there
The fans switch its self rarely is the issue as it just directs the resister to send x amount of power to the fan much the same way a switch operates a relay the switch doesnt pass heavy current