GMC Repair: Blower motor stuck on high, gmc suburban, controller switch

Question
99 GMC suburban 5.8lt.  The blower motor was on low and just kicked into high.  I can not change it from this setting no matter where the switch says (hi,med,low)

Answer
Hi
Without having the vehicle I can tell you on that particular system the problem can be either the High speed blower relay, the blower resistor OR the HVAC controller (switch assembley). THERE also is a connector about 6 inches up from the blower motor. follow the blower motor wires up, and they'll join in a 2 terminal connector. (Behind the glove box area) That connector has a tendency to overheat, and when it does the blower will stay on high speeds. You can just splice the wires toghter for a temp. fix.
The blower resistor and high speed relay are mounted on top of the Air case, behind the glove box.
Of course the controller is in the dash.
Other than that, I can tell you, I have changed MANY controllers, and not too many relays or resistors.
I Hope this helps.
JUST ADVICE from experience.
Good Luck
Pawl