There are two inline fuses located in the fuse box that need to be replaced.
I believe one of the fuses goes to the radio and the other to the ACC climate control. Not 100 percent on this.

My Servo will not turn on and I'm not getting any heat out of the vents

I found the bottom link and I'm not able to find them at my local Radio Shack.
1978-1980 300SD (W116) ACC fuses

Any advice is greatly appreciated