1716
5.7 Flame Sensing
The ame is detected by a method often called “ame
rectication sensing”. A gas ame is slightly conductive
and by applying a voltage to the spark electrode, a small
current will ow through the ame to chassis ground.
However, the ame conductivity depends on the polarity
of the applied voltage. A positive voltage on the electrode
will result in a higher current than a negative voltage. This
“rectication property” of the ame is used to distinguish
it from leakage currents that could be caused by dirt or
moisture. To detect if a ame is present, a high frequency
AC voltage is applied between the burner and the elec-
trode. This results in a net current in the forward direc-
tion if the ame is present, but no current if the ame is
not present. The rectication property then causes that
the electrode will have a slightly negative DC voltage that
is detected by the ignition control module. The AC volt-
age and the resulting negative voltage are not possible
to measure with normal methods, as the impedance is
too high.
5.5 Interior Fans
Connection Block
Both compartments have fans to help distribute the tem-
perature evenly throughout the unit. These fans are DC
operated and are connected directly to the lower power
module. Both fans run continuous when the ON/OFF
switch is in the “ON” position and the doors are closed.
The fan in the fresh food side will run when the door is
open, however the freezer side is stopped during opening
of the door. The fans can be tested by applying DC power
directly to the power leads.
Fresh food fan:
Remove the P4 connector from the lower control
board. Apply 12 volts DC directly to pin 10 red wire
(+) and pin 5 black wire (-). The fan should run. This
test can also be performed at the terminal connection
block just below the fan assembly. If the fan fails to
run, it will need to be replaced.
Remove the P5 connector from the lower control
board. Apply 12 Volts DC directly to pin 4 red wire (+)
and pin 1 black wire (-). The fan should run. This test
can also be performed at the inter-connection box
along the back wall behind the ice maker assembly. If
the fan fails to run, it will need to be replaced.
Freezer fan:
In order to prevent the circulation of warm air throughout
the compartments and to reduce the current draw on the
DC supply, both fans will be stopped after approximately
10 seconds if a source to heat the cooling unit is not avail-
able (e.g. No AC detection and failure to lite on gas “ch
LP”) in the front display panel.
5.6 Thermo Fuse
The NDA/NDE 1402 cooling unit has a thermo fuse lo-
cated on the boiler. The function of the thermo fuse is to
shut down the control system in the event of a cooling
unit problem. On certain units the fuse can be reset by
pushing the button in the center. The thermo fuse is a non
replaceable component of the cooling unit. When the fuse
pops, it is normally an indication the cooling unit has a
problem and the cooling unit will have to be replaced. To
test the thermo fuse, check for continuity. Lack of continu-
ity would indicate a faulty thermo fuse.
Thermo fuse
on boiler
Note: A disconnected or faulty fan assembly will result
in an error code displayed on the front display panel. See
section 11 for trouble shooting error codes.
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