Have not had this truck for long and finally getting around to sorting out the HVAC system. At first the vents would only blow from the upper dash (defrost), fixed the vacuum line that goes into the firewall and the switch selects vent location properly now. The problem I'm having now is that the blower motor will only turn on when I remove the plastic knob and pull the metal stud out. I can turn the switch to all settings and hear it change behind the dash, but no blower motor. Once I remove the knob and pull the stud it turns on ans works perfectly. Very odd, I guess something is not making contact. Is this a common problem? Anyone know what this could be? Do I need a new climate control unit?