Hi D.,
At some time past a year, babies do go to one nap a day, your son is right on target. Usually it's the morning nap that is eliminated, and they start to eat an early lunch and go in for their nap. You may need to play around with times to see what works best for him, and your daycare should be open to that. At this age, they need to sleep when they're tired, it's different when they're 3 years old and there's a standard "rest hour." I would suggest on days that he is with you, be out somewhere doing an activity (not pushing him around in his stroller or riding in the car) at the time that he normally gets sleepy, to try to push the start of naptime back. You may find that things adjust themselves, that if he naps earlier in the day, he may be ready to go to bed earlier or that he sleeps later in the morning and then is able to cope with the later naptime. And sometimes there is just an awkward stage, where they are done with two naps, but yet not quite ready for one. Your daycare may be able to suggest some good transitioning tips.
Good luck!