Specifications

DEFROST HEATER
AND THERMOSTAT
Top Mount
Models
These
models
use a radiant heater
to
remove accumulated
f rost f rom the
lreezer
evaporator and drain
trough
during a defrost cycle.
The defrost timer
energizes
the defrost
heater
every six or eight
hours
of
accumulated
compressor
run
time. When
the temperature in the thermostat
area
reaches
approximately
+
47o F the
thermostat
contacts open
the
circuit to the
defrost heater.
The
defrost
heater is
a spiral wound
resistance
wire enclosed in
a
heat
resistant
glass
tube.
lt is mounted in the
middle
of the evaporator beneath
an
aluminum
shield.
An
ohmmeter
check will
determine if all
phases
of
the
defrost cycle are
functioning
properly.
The
defrost
thermostat
contacts
open at approximately
+
47" F
and
close
at approximately
+
15o F.
The defrost
thermostat
may have either
a
47K
or 56K ohms resistor connected
internally across the two terminals. lf
so,
this resistor
permits
checking
the defrost
heater
even when the
evaporator
temperature is
*
15o F
or
higher.
An
ohmmeter can be used to test the
defrost heater
and
thermostat without
disassembling
the treezer
compartment
even if
the
evaporator
temperature
is
+
15o F
or
higher.
To
check
proceed
as
follows:
1. Disconnect the
unit
from
oower
source.
2. Disconnect the
plug
from the defrost
timer.
3.
Set
the
ohmmeter to the R x 1K
scale
and
connect
the
probes
to the No. 2
and No. 3 terminals of the
disconnect
plug.
4. The
meter should read
between
42K
and 63K ohms. The resistance is
not
critical. As long
as there is continuity
between Terminals No. 2
and 3 the
def
rost
heater is in
operative
condition.
lf there
is no resistance reading
(open
circuit)
the
defrost heater
and thermostat
must
be checked individually.
NOTE:
When
using
the
meter avoid touching the
probes
since
this
could result in
a
false
reading
and misdiagnosis.
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