You can block it. The unit won't heat or cool that room anymore though. The return air does effect supply air temp. And heat pump efficiency. With a 60 degree return air temp, the heat pump is more efficient then with a 70 degree return air temp.
We are simply getting contaminated causing otherwise healthy folks to lose the function of their kidneys and for a senior citizen who is already suffering sarcopenia this can be a death sentence because of the complexities associated with Renal Failure.
With Dying Breath The infamous lime green gas chamber at San Quentin, where all of California's death sentences are carried out. Today the room is used for lethal injections; California abolished execution by poison gas in 1995. Image courtesy of the California Department of Corrections and Rehabilitation.