I'm interested in electric cars and a specific model I'm interested is not equipped with a heat pump.... but does have AC. The discussion across the internet usually cites cost as a reason they did not include the heat pump. Given that an air conditioner IS a heat pump, and in their simplest forms the only difference is valving to make the refrigerant run in reverse, I assume that in practice there is something more complicated involved.
In practice, what are the differences between a "bi-directional" heat pump and a "uni-directional" AC/heat pump that would contribute to cost differences? I'm interesting in both specifics relating to vehicles, but also anything that might apply generally.
Sorry if this question is too engineery for this site?