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).
First locate the defrost clock. (They're mounted all
different places.) Remove it from it's housing.
Test 1: Turn the defrost clock over so that you
can see the back of it. Feel the defrost clock motor. Is it warm?
The timer motor that runs 24 hours a day. A good motor will be warm,
unless it's mounted in the cold compartment.
If it is mounted in room temperature air and there's no
sign of warmth, replace it.
Test 2: Often the back of the defrost clock has
a small window. Peering through the window it is possible to see the
armature of the motor spinning. If you can see the motor through the
little window and the armature has stopped, again you know that the
clock is bad. In other cases, a small rotating shaft is visible in
the center of the advancing knob.
If the defrost clock is warm and there is no window to
confirm that the clock motor is spinning, then another method is
employed.
By the way all of these tests can be done while the
refrigerator is still running. Take care not to touch any exposed
terminals of the clock to any metal or your fingers. Most often, the
spade ends connecting the defrost clocks are in insulated housings.
Test 3: Turn the clock back over so that you're
looking at the main shaft. With your fingernails or with a
wide-bladed screwdriver, slowly advance the defrost clock until you
can hear it audibly click. The loud click indicates the beginning of
the defrost cycle. At this point, two things should happen.
The compressor shuts down and the defrost cycle begins.
Sometimes when you try to advance the clock, it's extremely tight.
Again, it's a bad clock.
Assume that it turns easily, the motor is warm, and the
refrigerator is now in the defrost cycle. Remember at this point, the
evaporator is badly frosted.
Defrost heaters make a noise. Listen carefully for a
crackling and faint popping noise as the snow begins to crack from the
heat of the defrost heaters.
Test 4: Using a penknife or a sharp screwdriver,
carefully mark the position of the defrost clock. In fifteen minutes,
it will be possible to detect if it has advanced. If it doesn't
advance replace the clock.
