at the fan. in addition, it's recommended that lint traps be placed before the fan itself which has to be cleaned out frequently. these can also easily be overlooked.
this means that the moist air is not escaping correctly and that is why it is taking so long to dry your clothes - if they dry at all.
a good start at cleaning out lint blocked areas, i suggest go to the back of the dryer and take off the vent pipe or hose and check things out with a flashlight. clean out all the lint and dust you can, even use a vacuum cleaner on it. make sure the vent pipe 