Test Defrost Timer # 9 in this download http://www.appliancepartspros.com/partsearch/frame_diagram.aspx?diagram_id=28327585&pkw_=basket&model_id=5167318&NewWindow=1
The defrost timer is usually found in the temperature control console.
To test whether the defrost timer is simply failing to advance,
locate the advance screw and turn it clockwise until you hear it click.
This advances it to the next mode.The freezer fan motor should have stopped now
in defrost mode. Simply wait about 35 minutes and check whether it has moved out of defrost mode and has resumed cooling (listen for the compressor and freezer fan motor).
If it does not advance, the timer motor is probably bad and the entire
timer needs to be replaced. If it advances as it should, then you can
follow the steps below to test the switch electrically.
The timer is usually held in place with one or more screws. Remove
the screws and gently pull the timer out far enough to disconnect the
wiring connector. The connector can be removed by firmly pulling and
rocking it left and right. It is not necessary to note the position of
the wires because the connector plug is keyed so that it can be replaced
in only one way.
Test the timer for continuity
using a multimeter
Set the multimeter to the ohms setting X1. The timer has four
terminals. Locate the common terminal, it should be labeled "3" or "C".
If the terminals are not labeled, determine which terminal coincides
with the white wire in the connector plug.
Once you have located the common terminal, touch one probe to it.
Touch the other probe to each of the three remaining terminals. The multimeter should display a reading of zero or near to zero ohms
(which indicates continuity) for one pair of the terminals and possibly
two pairs. The third pair of terminals should show no continuity