i have a 1500 Silverado that is having a/c and heater issues....the temperature selector and vent controller stopped working...the blower speed selector switch and vent/recirc selector buttons work...I have already replaced the entire control unit in the dash but the system is stuck blowing hot air thru the defroster vent....i cant change temperature or get the vents to change....is there something common to both the temperature control and vent selector that would cause this issue? thanks in advance WSM Gurus!...

Carlos