My two children were never on a nap schedule when they were infants. I stayed at home and just let them sleep wherever they wanted and when they wanted. I know that probably wasn't the best idea, but I do have to say that they can now fall asleep wherever we are and they stay asleep! I feel that they are very well-adjusted and flexible children. However, they are now on a nap schedule.
I started a home daycare in June and it was very important for me to get all of the children on the same schedule, so that I could have at least a little break during the day. I made our daily schedule predictable and consistent. We always eat lunch at the same time, then we change diapers and then we ALL go down for a nap. We do this everyday without fail. They all sleep for 2.5 hours or MORE:) I do have a seven month old that I watch and she did not fall into our schedule until recently. Once she was eating solids at the table with us, she fell into our routine. She eats her food, has a bottle and then goes to sleep for two hours. It is all very predictable to her and if I am only a few minutes off, she is screaming. I guess what I am trying to say is to be consistent and the rest will follow. He might not sleep the first few days, but you need to lay him down at the same time and try to leave him there for however long you would like him to sleep. If he cries for more than ten minutes, I myself, would probably cave in and go get him. But, the next day do the same thing, etc.
I don't know if you have a sitter or not, but you definitely need to be on the same page as her. She needs to do the same routine as you do on the weekends or on your days off. If he does go to a sitter, it might be wise to ask what their schedule for the day is. If she is not consistent with him, it will not work. I am sorry this is so long, but hopefully some of the information was helpful.