97 GMC K1500 XC A/C not working - electrical

[Danielroper918]

I am having similair issues with my 1997 Chevrolet C1500. The blower motor only works on the two speeds in the middle (low and high dont work) also my recirc and AC buttons do not illuminate.i have replaced the control head twice both were used however the first one came out of my dads old truck the AC worked in AC worked for 2 weeks then it wouldnt engage clutch or switch from floor to vent to defrost nor switch temperature. I bought another one from a salvage this past weekend and the recirc light lit up for a split second then nothing. If i jump 87 to 30 my AC clutch will engage. My question is what voltage do i need to verify for the head unit as im sure my head unit is fried. I just dont want to buy a new head unit if there is something else shorting it out. I might also mention that my "new" (salvage) head unit will operate all modes except fan speed and AC/Recirc.