Hello and welcome to just answer my name is ***** ***** I will be the one to assist you. When it comes to heating in a dryer there are a few things that can be the problem.
Defective Heating Element
The heat produced from heating elements is measured in watts and a normal heating element will produce about 4500 watts of heat. If the heat element is shorted to the case, this will cause the heating element to operate on 110v and use only about 1/2 of the element wire. In effect, the heat produced will be only about 1/4 of the amount that should be produced and the end result is an increased drying time.
The normal method for checking a heating element is to check it continuity. With the element unplugged you can check the continuity from one wire post to the next. If the circuit is open, then he heating element is faulty.
However keep in mind that the element could be shorted to the case as described above. In this situation it is possible to have continuity, but the element still be the source of the problem.
Defective Thermal Fuse
The thermal fuse is in series with one leg of power to the motor. If the fuse is open (no continuity) the motor will not run.
The thermal fuse is located in different locations according to the model and brand of dryer.
Check the thermal fuse for continuity with a volt/ohm meter. If it is open, it will need to be replaced.
The thermostats are responsible for maintaining the proper temperature in the dryer. Check the exhaust temperature of the dyer and if the temperature is above 150 degrees, you will most likely need to change the operating thermostat.
The thermostat can also fail in the opposite mode. It can prevent the element from heating at all. A failed continuity check at room temperature will verify this condition.
There are some special thermostats that are single pole double throw. These thermostats are often used to control the timer when set to the Automatic Dry cycle. If the dryer timer will advance in the Timed Dry cycle but not the Automatic Dry cycle, then the thermostat could be the problem.
Thermal Cutoff Defective
The thermal cutoff is a one time blow protective device. It is usually located on the heat element housing and monitors the heat output. It is a secondary protective device. The high limit thermostat should open if the heat exceeds the range of the thermostat , but in some cases the thermal cutoff will open. This will normally occur if the vent system is restricted or if the operating thermostat is not opening at the proper temperature. Check them both to ensure adequate air flow and exhaust temperature. You can test the thermal cutoff for continuity. If it show to be open it will need to be replaced.