75 blazer A/C components

[eighteenninetytwo]

Hi all.

I changed out my old and non function A.C unit for an A/C delete heater unit. now I'm finding that I cant turn it off and it will blow hot air WHATEVER because the vacum tubes aren't operated by the new control unit i bought so wont control the mechanisms to close the doors.

Turns out that behind the Control unit there is some form of rotary switch that is missing on my truck, that controls the vacum tubes and enables me to shut off the hot air. I can't find this anywhere (probably because i don't know what its called) but the thought occurs that any 73-75 C10 / C20 or K10 / k20 with A.C would have the same controls and control components installed right?

Am I wrong in this and does anyone know what I'm talking about with this rotary switch thingy?