hi A.;
i hope my other attempt to respond didn't accidentally post half way thru; my kids freak out when i go on the omputer!
anyway i would suggest this; never stop offering the nap. my son, 3, didn't nap for several months, then his activity level changed dramatically and now he will nap almost every day, given the right circumstances. i would say you should make sure your son is getting the MOST PHYSICAL ACTIVITY POSSIBLE. my son is happiest, and most nappable, when we spend nearly all our time outdoors, or if that's not an option, at indoor play centers or spaces where he can really run around and move freely. an active child who 's had a nap is the best kind. a frustrated child who's bored and itchy and overtired can wreck your life.
my daughter, 17 months, is pretty much the same. she has to have a lot of activity in the morning, even if that's just pushing her dolly stroller around in circles at the playground for 45 minutes and then a play-bath.
that's another major help, esp. in summer when the kids are sweaty and it's too much sun or too hot outside, come in for a cool playbath, no washing needed, just let them play in the tub for as long as they want. after that, make sure your son is hydrated, have a light snack, turn the lights low and put on a calming DVD like Teletubbies or Winnie the Poo, Curious George is good, and let him sack out on the couch.
good luck,
J.