Can I get some EXPLICIT steps on doing an AC delete?

[projo198]

I've been trying to get a solid answer online and have had no luck.

My '78 K10 came to me with the outer heater box completely tore off. The only thing still there was the blower motor and housing.

I want to run heat only, no interest in restoring the AC (if it ever existed). The controls in the cab do show AC selections so I am guessing at one time it had it.

I have seen aftermarket "AC delete" boxes which appear to just connect the blower motor with the large square door in the firewall. I am in the process of fabbing my own to save money.

Is this job literally that simple? Does it require any modifications inside the cab?

Pic of my firewall. Any help/advice would be appreciated!