I'm going through the same thing with my 14 month old daughter. She used to sleep great, but her afternoon nap is disappearing. I think she's a little young for this, so I will continue to put her down for her afternoon nap for a while and hope it's just a phase. She is so tired later in the day if she refuses her second nap, so I know she needs one. Her schedule is something like this: 7:00 wake up, 9:00-10:30 nap, 1:00-2:00 nap, 8:00 bedtime. It varies a little based on when she woke up. Sometimes the naps get pushed back because of a late wake-up time, but bedtime is always 8:00.
If you decide to transition to one nap (and maybe he is ready for that: follow his body cues) then try pushing back his morning nap bit by bit. Keep him up an extra 30 minutes before laying him down for a couple days until that becomes the new naptime. Then push it back again until it's sometime mid-day.
Perhaps instead of naptime, you could make the afternoon a "quiet time". Put him in his crib with a couple of books or favorite toys and leave him alone for 45 minutes or an hour. That way he has something to play with and won't be screaming, but he also learns that he is still expected to have some down time every afternoon.
Good luck!