A bad door switch could be the reason why your Whirlpool 29 inch electric dryer is not starting in any of the cycles that you try it on.
This switch is use as a safety device that opens the motor circuit preventing the motor from running if the switch is bad or if the dryer door is opened.
It protects the user from getting hurt by turning the motor off. if the door is opened during a drying cycle.
To check it out visually do the following. Open the door on the dryer and inspect the switch lever to see if it is broken or not. One of the reasons why the lever breaks, is because the user let go od the door and the door closes too hard on the lever breaking it. If the lever is broken, the switch is bad and must be replaced.
If the lever is not broken, then you will need to check it for continuity when the switch is on the on position.
To check it do the following. Disconnect the dryer from the wall outlet. Open the top panel, disconnect the switch from wire harness. Set your multimeter on the lower scale to read ohms.
With the door closed take a reading between the 2 terminals on the switch. The reading should be close to 0 ohms. If the reading is infinity, the switch is bad and must be replace.
To replace it open the door and remove the 2 holding screws and take it out. Set the new one in place and secure it with the 2 screws. Connect it to the wire harness and close the top panel.
Connect the dryer to the wall outlet and try it o see if it works ok now. Don't worry about understanding these instructions. Just watch the video below and you will see exactly how it is done.
Below are the links to the parts needed for this repair.