In sci.electronics.repair DaveC wrote:
I presume the way 3 heat settings are accomplished is through the use of
2 different wattage heater elements. For example, Low = 1000w element;
Medium = 1500w element; High = both elements.

This may be right. Another way it can be done is with two equal wattage
elements. Low = one element across 120 V, medium = one element across
240 V, high = both elements across 240 V. More common in electric ranges
that have off-1-2-3-4 pushbuttons instead of "infinite" heat controls,
but possible in a dryer.

How is it possible for the dryer to fail in a mode that results in only
medium heat?

Using your assumption, "low" element open, or faulty temperature switch.

Just trying to get a few ideas before opening it up.

Open it up. Most GE washers and dryers will have a schematic folded
up and taped somewhere inside the control panel. If you can read this
and drive a DVM, you can make some tests of the switches and the elements
at the control panel wiring, before having to pull the drum out to get at
the elements. Unplug the dryer first and watch out for sharp edges of
sheet metal inside it.

Matt Roberds