I replaced the heater fan recently. The replacement was a Siemens, but now the fan performance is anemic. It makes lots of noise but the air coming out of the vents is weak, even at the high setting. Fan rotation is correct, and I cleaned the dirt and crud out of the evaporator as best as I could. The problem doesn't appear to be electrical (the fan seems to get up to speed). The air isn't being shunted to defrost or to the feet. Not sure what to do next.