Problem is simple and a very common one at that.
If in doubt do not attempt to take dryer apart make sure who ever is doing this is competent.
You will find it is either your heater element which i very much doubt!
Or most likely this will be the thermostat.
The reason thermostats do tend to blow is usually opening and shutting the door before the dryer has stopped causing cold air to rush into the dryer. Also another common fault which is also a fire hazard lots of fluff in the bottom or around the element area. make sure this is always cleaned out and the dryer regularly serviced.
Carlito Corway It does what it says on the tin, February 2007