here are some possibles causes to check
door interlock ,main motor , heater element,
remove the jack plug from main motor
remove the wires from heater element.
making sure no wire are catching /touching,turn on the supply, if it stays in one of these components is faulty,
power off pick one of the two and reconnect wires/or the jack plug apply power if it trips this is the FAULTY component if the supply stays in suspect other one prove it my swapping and testing the other component in the same way (disconnect the good one connect the other one apply power , power will kick immediately change component don't know a test for a door inter lock
usually just put a replacement one in
wirecutterman, June 2009