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Replacement parts for WHIRLPOOL LER7648KQ0 | AppliancePartsPros.com

The operating thermostat (Item 8 in Section 3) shows that it should open at 155 degrees F. This would be the high heat setting.
Lower heat settings turns on it's internal heater, adding heat to the thermostat and resulting in lower machine heat output.

If the unit runs at the same temperature all the time it could be that the operating thermostat's contacts are welded together.

Also if your vent system is partially plugged it will sometimes give the appearance of high heat though you would also see poor drying results and you did not mention this.

Another common cause of high and non-settable heat is a grounded element.
Check the heating coil.
Unplug the unit and both wires to the coil.
Check it with a meter, should be around 10 to 12 ohms.
Then check from each side of the coil to the case/frame, both should be infinite ohms (open). If not the coil may have sagged or broken and is touching the case. This can cause it to run on high and the thermostat cannot regulate it.