help with over heating

hi i have a 02 PT cruiser just yesterday i changed the transmission fluid and filter,oil and oil filter,and tune up put new sparkplugs in it...well when it was all done and finshed seem to run good then i guess the fan for the radiator is kicking on to keep it cool...had some one test the fan and it kicked on i was wondering if someone could maybe know whats happing i put a new coolant sensor on it...but it still wont turn on the fan any ideas thank you