Postby smj999smj » Sat Feb 10, 2018 7:04 am
Well, you really can't tell if any part is bad without testing them or doing the diagnostics to isolate said parts as the problem, except for substitution a known good part; that goes with just about any failed part, regardless of what it is.
If you have manual heating and air-conditioning, which is pretty rare, you'll have a blower resistor. If you have auto climate control, you'll have a VBC, also known as a fan blower amp or "variable blower control." When a VBC fails, it often goes to "fail-safe mode," where it has the blower fan run at full speed all of the time. If a blower resistor fails, the blower fan will usually run when set to the highest speed setting, but won't work on lower speed settings. If the blower fan doesn't work at all, that could be one of several things, from a bad blower motor, blown fuse(s), bad relay or HVAC control head or a shorted or open wire. I that case, I would first check the fuses. If the fuses are good, unplug the blower fan and check for power to it with a 12v test light (make sure the key is "on" and the HVAC system is "on." If there's power, you can run the test lamp between the two terminals of the harness connector to test for ground. If you have power and ground but the fan doesn't work, replace the blower (sometimes you can bang on the blower motor and get it to work). If there is no power or no ground, then you'll have to do some diagnostic work, including circuit checks. I would recommend referring to the factory service manual.