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Parts for Whirlpool WED5540SQ0 Dryer - AppliancePartsPros.com

See the attachment for the tech sheet.

When in timed dry does the timer advance to off?
The timer runs on 220 and should advance to off if there is 220 in the unit.

Unplug the unit and attach one meter lead to L1. Best place is at the line cord plug.
Set the unit to timed dry, high heat mid cycle.
Set your meter to the most sensitive scale and short the meter leads together to see if there is a zero offset in the meter.
Now work your way back through the heater circuit.
Both sides of Timer Switch 2 should be 0 ohms.
Both sides of the Thermal Cutoff should be 0 ohms.
Both sides of the Operating Thermostat contacts should be 0 ohms.
Both sides of the Hi-Limit Thermostat should be 0 ohms.
Hi-limit side of the heater should be 0 ohms.
Other side of the heater should be 8 to 12 ohms.
1M on the motor's centrifugal switch should be 8 to 12 ohms.

If all are OK then all that is left is the heater centrifugal switch on the motor.
You could check from the plug L2 to 2M on the switch just to be sure that it is not a bad wire/connection.

If all OK then odds are that the centrifugal switch is toast.
It could be a problem with the centrifugal mechanism (lint etc.) or the switch.
You may need a new motor.