1992 Olds Ninety Eight Regency Elite A/C

3.8l V6 34,500 miles
frontwheel drive

a/c was not blowing cold
changed system from r-12 refrigerant
Control head would not engage system(option code
C68)
Tried 2 used heads but auto setting will not engage
dealer wants $800 for componet

Is there another switch ,sensor, or module that me be the problem