Norcold N611V SERIES Service Manual page 11

Background Operations - cont'd.
Moisture Reduction Heater (Divider Heater)
The divider heater is a low wattage heater used to reduce/
eliminate sweating on the surface of the plastic area between
the freezer and fresh food compartments, i.e. the divider
area. Due to the cooling nature of the refrigerator, the divider
area, especially on hot humid days, tends to be cooler than
that of the air around it. This causes the divider surface to
be below the dew point of the surrounding air and as a result
moisture or sweating develops. The divider heater, which is
not replaceable because it is foamed into place, consists of a
resistance wire placed atop one side of an adhesive backed
piece of foil adhered to the back of the divider area. Applying
12VDC to the resistance wire causes the wire to warm up. As
the wire warms up heat is transferred throughout the area of
the foil and subsequently the divider area. The added heat to
the divider area keeps the surface temperature above the dew
point of the surrounding air thus eliminating the occurrence of
sweating.
Theory of Operation - Moisture Reduction Heater (Divider
Heater)
The divider heater is connected between the power board
at P1-8 and the optical display board at P1-5. When the
refrigerator is fi rst powered on the power board measures the
value of the DC input voltage and communicates this value to
the optical display board. Providing the value of the DC input
voltage is greater than 10.5VDC the optical display board will
request the power board to turn ON relay K5. Anytime relay K5
on the power board is turned ON, 12VDC passes through the
now closed K5 contacts to terminal P1-8 of the power board
and out to one side of the divider heater. The other side of the
divider heater is tied to 12 volt ground via the white/violet wire
connected between P1-4 of the optical display and P2-4 of
the power board. Anytime the optical display senses the door
is open, it requests the power board to turn off K5. Once the
door is closed the optical display will request the power board
to turn K5 back on. Anytime the DC input voltage falls below
10.5VDC the optical display will request the power board to
turn off K5. Anytime K5 is turned off due to low DC voltage it
will not be turned back on until the DC input voltage has gone
above 11.5VDC.
Backup Operating System (BOS) Mode
The refrigerator has the ability to continue cooling in the event
the thermistor (temperature sensor) becomes inoperable.
Should the thermistor become electrically open or shorted the
electronic controls will revert to this backup operating mode,
allowing the refrigerator to continue cooling until it can be
serviced.
Refrigerator Service Manual
Theory of Operation - Backup Operating System (BOS)
Mode
The power board measures the thermistor value and
communicates it to the optical display board. Should it
sense the thermistor is inoperable (electrically shorted/open,
unplugged, damaged, etc.) the optical display board will
activate the BOS mode. While operating in the BOS mode the
thermistor will be ignored and the temperature set point will be
interpreted as a duty cycle instead of a temperature setting.
This duty cycle will maintain refrigerator cooling by controlling
the length of time the heat source outputs (AC heater, LP
burner) are energized.
While operating in the BOS mode the unit will operate on an
80% duty cycle. The cycle period is 1 hour, translating to an
ON time of 42 minutes and an OFF time of 12 minutes.
Defrost Operation
Although the refrigerator is NOT frost free, it is designed to
limit frost build up on the fresh food fi ns (metal fi ns mounted
on the back wall of the fresh food compartment). This is done
by simply turning off the heat source output, which in turn,
momentarily suspends cooling. As the fi n temperature rises,
the frost melts.
Theory of Operation - Defrost Operation
Every 49 hours of operation the refrigerator will enter a defrost
mode. While in the defrost mode the power board monitors the
thermistor value, reporting it to the optical display board. If the
thermistor value is greater than 38°F the optical display will
exit the defrost mode, reset the 49 hour timer, and continue
normal operation. If the thermistor value is less than 38°F the
optical display will request that the power board turn OFF the
applicable heat source output, be it the AC heater or the LP
gas burner, until the thermistor value reaches 38°F. Once the
38°F requirement is met the optical display will exit the defrost
mode, reset the 49 hour timer, and continue normal operation.
Auxiliary Output
The auxiliary output is used to power auxiliary loads such as a
fan or waterline heater. The voltage at this output is whatever
the DC input voltage connected to power board terminals
12VDC and GND is. That is to say, if the DC input voltage to
the refrigerator is 11VDC then the auxiliary output voltage will
be 11VDC.
Theory of Operation - Auxiliary Output
When the ON button of the optical display board is pressed,
relay K3 on the power board is turned ON; see On-Off Theory
of Operation (page 16) for detailed explanation. Anytime relay
K3 is ON, the DC input voltage connected at the refrigerator
(terminal 12VDC) passes through the now closed K3 contacts
to terminal P1-5 of the power board. The DC ground connection
(terminal GND) is electrically tied to power board terminal P1-3.
This auxiliary output will be present anytime the refrigerator is
ON.
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11
N611v, N811v Models