since i bought my car, i noticed that the a/c and heater control unit only blows out at one speed. the speed adjustment doesn't work. I bought a brand knew logicon control unit, and after putting it in it still blows only one speed. please any help on how to fix this would be appreciated.

 

Going from memory: There's a power transistor on a heatsink in the ductwork somewhere near the blower motor that gets a signal from the logicon. The transistor is actually what modulates the power to the blower motor for any speed other than high. High speed is controlled by a relay mounted in the same area. I'm thinking your power transistor has died, and it is defaulting to high.