low blower motor not blowing

First symptom - high blower motor blowing even with key out of ignition, so I took out high-blower fuse.

2nd symptom - lower blower motor now just barely moving air on any speed. If I put high-blower fuse back in, then the blower motor functions at high speed.

3rd sympton - if I turn blower motor to off position, actually can hear it stop whisping air.

I replaced the temperature control unit in the dash, to no avail. Wondering if there is some temp sending unit that has gone bad, or where to access the blower motor to check wiring connections.

thanks,

ac