I've looked for a defrost timer
and can't find one in the refrige..
CY: if it's a mechanical timer, it's probably in the box with the
control knobs.

I would like to know if the defrost
timer is part of the primary circuit board accessed from the
back of
the refridge?
CY: Some newer fridges have a board, others use a mechanical
timer.

Is the defrost heater and defrost thermostat accesed from
the panel at the rear of the freezer compartment?
CY: Yes, and the freezeer section is usually narrow. Makes for
some strange twisting and bending to get at it.

I assume it is
probably one of these parts and would like to know how to test
which is
the problem.
CY: You can wait till it's frozen. manually advance a mechanical
timer, and then check the current draw. Five amps is about right
for a defrost heater. If it's not drawing five amps, very often
the heater and termination thermostat are replaced together.


Thanks for the help if someone can.
Garyf

CY: Y'welcome.