The fan for the heater or A/C stopped working. Doesn't matter what speed setting or if it's heat, a/c, ec, nothing blows out. How do I start troubleshooting this to see if it's a fuse (checked already, all good), rotary fan switch, fan motor, fan regulator/resistor, etc... I could replace it all but these parts are not cheap. I've heard the most common problem is the regulator/resistor. The car has 91K miles and it's a 1998.