[miwilson]

Our dryer no longer works on the automatic function. The dryer heats fine but the switch doesn't advance. The timer drying function works fine.
How does one fix this problem? Do I need a new timer switch or senor or what?

[Qtip]

does it take a long time to dry the clothes on the timed dry cycle? if so then disconnect the vent hose and run a load on the automatic setting without that vent connected and if it works then there is a venting problem.

[miwilson]

No, the normal timer mode seems to dry just fine. When using the automatic functions the timer will not advance.
Do I need to change out the entire timer assembly or what?

[denman]

Here are your parts
Front panel/lint filter replacement parts for FRIGIDAIRE FDE648GFS0 Frg(v1) / Dryer | AppliancePartsPros.com

Here is the wiring diagram
http://manuals.frigidaire.com/prodin.../131826200.pdf

Could be that the sensor is just dirty.
Note: I am not 100% sure about the following as I could not see the sensor type.
Usually the sensor is just two metal strips spaced about half an inch apart.
When the clothes are wet there is moisture between these strips, they conduct electricity and tell the unit that the clothes are wet, so do not advance the timer. When the clothes are dry there is no moisture, so no current flow, the machine senses this and the timer advances.

If there is dirt or lint between the metal strips the unit thinks the clothes are wet even when they are dry and the timer never advances,.
Clean the sensor with isopropyl alcohol or even a damp cloth. Just be sure to let it dry before trying it.