blower fan acting eratic on 2002 Volvo S40

the blower motor seems to have a mind of it own. speeding up and slowing down randomly in the munal mode as well as the automatic mode.I unplugged the blower motor resistor and plugged it back in and the blower wouldnt work at all anymore.I change the blower resister with a new one from volvo. having the same problem. any suggestions. Thanks

Asked by for the 2002 Volvo S40
I would check your blower motor ground circuit, it may be loose or corroded and I have seen that cause random blower speeds.