I’m seeing it spelled different ways. Wiki has it as “Amenguale” on Mr. Sierra’s credits and “Amanguale” on the Barney Miller page.
I just saw it written on the squadroom board as “Amengual.” Unless the spelling changed later in the show, there’s no reason to spell it otherwise. And with Chano being Puerto Rican, the name would not end in a silent E. (BTW, while “Amengual” is not an actual surname in Puerto Rico, “Mangual” is—it originated in Catalan-speaking Mallorca in the Balearic Islands off Spain’s Mediterranean coast, and was alternatively spelled “Mengual” in the old country.)