Heating/cooling works only on high?

I have a 1993 Buick Lesabre
A while back, my heating and cooling system stopped working - by heating and cooling, I mean my climate controls - so I shut off and turned the car back on, and they did the same thing - so, I thought it was my blower motor - went and got a new one, replaced it - same thing - got another one - same thing. So, I thoguht it may be the resistor pack. Got a new one, replaced it, same thing, no air movement. Got another one, same thing.
I even tried replacing the control panel (not sure of the real name - the thing with all the buttons and sliders that controls the climate stuff) in my car - same thing. I finally just unplugged the resistor pack, and now it works on high - but high only - help!