How to talk to a summer hook up?

Ok so me and this guys hooked up over the summer and were talking and I stopped talking to him for a short period of time but he still wanted to keep in touch after the fact and now that school has started I want to talk to him I talked to him once in the hall but it was just about cles and it had a underlining flirtation in it but now we see each other in the hall make eye contact and smile but I don't know how to talk to him and i cant (nor would i) avoid him cause we have to cross paths to get to our cles I know for a fact that he would talk to me but i think he's getting the wrong message from me which is causing him not to peruse a conversation so someone help me please