Can I use the defroster if I have bypassed the heater core?

You can buy an electric defroster for <$10 on sale at Harbor Freight. I recently got one for my son in San Diego since the heater core on his Mercedes 300D was bypassed when I bought it. He whined that it was marginal. Funny that same week, Car Talk handled a question from a lady in Santa Cruz. They said she didn't need a heater there, well maybe, but not if she lived in San Diego. I told him to pick a sunny day to drive back for Xmas.

I used an electric one for a while on several cars in Atlanta. At least it clears a peep-hole. That said, I got a new heater core for both my 65 Dart and 65 Newport recently. I recall ~$25 and $55, resp, maybe both from rockauto. The Mercedes is tougher since new ones "not avail" and people ask $50 for used ones. It is a funky 3-tube type with high-density fins and plastic reservoirs, similar to the Behr models for semis. Since no German winters here, I got a new heater core for a Caravan cheap that I will adapt.