The following method is one of the fastest, easiest, and
most reliable ways to diagnosis a frosted up evaporator. (For more
detail see Defrost Clocks and Heaters in Manual 7: Refrigerators).
With the clock set in defrost, current should be
flowing through the defrost heater. Other than the sound, there are
several ways to confirm, if in fact, the defrost heater is
operating.
In radiant heat models with glass tube heaters,
it is possible to see the red glow. Turn off any lighting and look
into the evaporator. Any sign of a red glow confirms that the defrost
limit and the defrost heater circuit are intact.
A second method is to jerk the refrigerator plug
out of the socket. Watch for a medium-sized blue arc as the current
flow to the heater circuit is cut off. A tiny spark indicates only
that the lighting circuit has been cut off.
A third option is to pull the defrost wire off of
the defrost timer and look for an arc.
Last, but not least: use an Amprobe and clamp it
around the defrost heater lead. There should be several amperes of
current flowing.
If, after performing one of these quick tests, you have
determined that no current is flowing through the heater system, then
either the defrost heater, the wiring is broken or the defrost limit
is bad. In most cases the defrost heater is the culprit.
If the defrost system does begin to heat up, you have
confirmed that the heating system is okay. The only component
controlling the heat is the clock. Conclusion, the clock must not be
advancing, as designed, and turning on the heat. Replace it.
