The first thing I would check are the thermal fuse (on the air duct) and the hi limit thermostat (on the heater).
If any of them is open - replace both. The new part comes is a kit of the thermal fuse and the hi limit thermostat.
- The part number for the thermostat kit is AP415996
- Here are the break down diagrams for the Magic Chef dryer Model YG20JN4