A/C Blower High Speed Only

[Dr K]

I hope someone can help here
2003 Expedition
Dual Controls for AC and Heat
Problem
Regadless if it's set to AC or Heat, Single on Dual control, manual or Auto setting for temp.
the blower is not running unless I press the fan button manually to the max setting
Temp's are OK just the speed of the blower.
Is there a vaccum control line, resistor or????
BTW How do you perform the Self test on this unit?
I tried OFF+FLOOR and AUTO after 2sec. No luck ( it worked on my previous exporer this combo)

Thanks