PagneKilla

I have a 99 tl with a navigation system. However I was sold the vehicle without the navigation unit. The navi is missing from my trunk. The navi screen never comes on, the screen stays black. I was told to buy a new navi unit to power my screen. Now today I was told my screen should still come on without the unit in the trunk is this true? I really need help here im becoming frustrated. I just want to be able to power on my a/c