M.L.
I suggest that instead of telling him/making him nap, tell him that it's quiet time. A time for him to sit and "read" on his bed. Or even play quietly there.
Let him know he doesn't HAVE to sleep, he just needs quiet time. Maybe even say that you need that time too.
Sit down with him. Lay on the couch together and cuddle for a bit. He may not need the nap as much as he just needs a time for his body to calm itself for awhile.
At this age, one nap/quiet time should hold him over till bed time. He may also be just trying to control his environment the only way he can.
Hope you are able to figure out something that works for both of you.