Intermittent heater Blower 93 taurus Sho

[jada]

The problem that I have is that the heater blower fan stays on at times. The electronic head unit shows off but the fan stays on. and also when it is working properly it works on high and low speed only no medium. I ran a diagnostic on the a/c system but it shows no codes...I thought that the electronic head unit could be bad. Is there a fan speed switch, any help would be appreciated.