1991 GMC k1500 heater temp control problem

[bison1973]

I can't adjust the heat temp on this truck ('91 GMC). It air coming in is stuck on hot. It has the electronic heat/ac control box. All controls work except for adjusting the temp. The little pointer moves from H to C but the air temp coming into the cab dosen't change. I purchased a used control box that came out of a '94 GM truck but it does the same thing. The only difference is when you try to adjust the temp down the entire temp pointer bar on the control box lights up and repeatedly flashes. Is it the control box or is there something else that needs to be fixed? Anyone have any info or can anyone point me in the right direction to fix it.

Thanks in advance,

Tim S.

[bison1973]

Hey, does anyone have any ideas? I'm just looking for a little help here.

Tim