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.
Since the death penalty was reinstated in 1977, about 70 of the state's condemned inmates have died of natural causes. Another 24 killed themselves. (In the last 10 years, the suicide rate on California's death row was 15 times higher than the statewide rate.) About half a dozen condemned inmates died from other causes like drug overdoses and murder.