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10
Refrigerator Service Manual
NX6 / NX8 / NXA Models
Electronic Controls
A precise heat is applied to the boiler area of the cooling
unit causing a chemical reaction within the cooling unit that
ultimately results in the refrigerator cooling. The heat applied is
done so by means of:
•
Cartridge type heaters (AC or DC heaters)
positioned in heater wells welded to the surface of
the boiler
•
LP Gas burner positioned below the boiler such
that the heat from the
fl
ame is directed across the
surface of the boiler
These heat sources are turned on/off via the combination of
the electronic controls and a temperature sensor located inside
the refrigerator fresh food compartment. A temperature setting
is set at the electronic controls and as the temperature sensor
warms and cools the heat source is turned on/off accordingly.
This process of turning on/off the heat source(s) can be
accomplished in various operating modes. These operating
modes are:
•
Manual AC Mode - While operating in this mode
the AC cartridge type heater is operated to provide
heat to the boiler area of the cooling unit (2-way &
3-way models)
•
Manual LP Gas Mode - While operating in this
mode the LP Gas burner is operated to provide
heat to the boiler area of the cooling unit (2-way &
3-way models)
•
Manual DC Mode - While operating in this mode
the DC cartridge type heater is operated to provide
heat to the boiler area of the cooling unit (3-way
models only)
•
Auto Mode - While operating in this mode the
electronic control will automatically select the
mode to be utilized. It will attempt to operate the
heat source requirements in the following order of
priority (All models):
•
1st Priority Choice - AC Electric (AC cartridge
type heater)
•
2nd Priority Choice – LP gas (LP Gas Burner)
•
3rd Priority Choice – (3-way models only) - DC
Electric (DC cartridge type heater)
Dependent upon the model number NX6X/NX8X refrigerators
are either considered 2-way or 3-way model refrigerators
(See Model Identi
fi
cation section of this manual). 2-way
refrigerators are capable of operating priority choices 1 and/
or 2 via separate Manual Modes or an Automatic Mode. 3-way
refrigerators are capable of operating all 3 priority choices via
separate Manual Modes or an Automatic Mode.
The mode of operation and temperature setting is selected
via the optical display assembly located on the front of the
refrigerator. A thermistor is mounted on the
fi
n assembly
located inside the fresh food compartment. The thermistor
acts as a temperature sensor, reporting the temperature
sensed to the optical display. The optical display then relays
this information to the power board that then turns on/off the
appropriate heat source accordingly. The optical display board,
power board, thermistor, and other components within the
refrigerator are interconnected via a wire harness.
Manual AC Mode
To operate in the Manual AC mode the optical display must be
placed to operate in this mode. Once done so, the refrigerator
will cool via the AC mode and ONLY the AC mode. While in
the AC mode the refrigerators electronic controls will function
as follows:
The power board is responsible for:
• Measuring the AC input voltage
• Measuring the AC heater current
• Measuring the resistance value of the thermistor
• Turning ON/OFF the AC heater output
• Communicating with the Optical Display Board
The optical display board is responsible for:
•
Determining if the AC input voltage is available or
not available
•
Determining if the AC heater current is acceptable
or not acceptable
•
Determining if the thermistor value is above or
below preset temperature range cut-in/cut-out
values
•
Determining when the power board is to turn ON/
OFF the AC heater output
•
Communicating with the Power Board
AC voltage is applied to the power board via the AC power
cord at terminals L1 (Hot) and L2 (Neutral). This AC voltage
passes through the AGC Series, 8A, Fast Acting, Glass Tube
Fuse (F2) where it is then measured. This measurement is
communicated to the optical display board which determines
if the applied voltage is below or above 85VAC. If the voltage
is above 85VAC, the determination is that AC voltage is
available. If not, it is determined that AC voltage is not
available and the appropriate voltage related fault will be
displayed on the optical display.
•
NX61 / NX81 = Power ON indicator is Solid RED
•
NX64 / NX84 = "no AC" with audible alarm/beeper
•
NXA64 / NXA84 = "no AC" with audible alarm/
beeper
The power board also measures the thermistor value and
reports it to the optical display board. The thermistor, a
temperature device whose internal resistance goes down as
the temperature goes up, is connected to the power board via
terminals P2-1 and P2-6. The optical display board compares
the actual thermistor value to preset cut-in and cut-out
temperature values for each of the particular temperature
settings. Should the thermistor value fall below a particular
cut-in value it will request the power board to turn ON the AC
heater relay (K2). Should the thermistor value go above a
particular cut-out value it will request the power board to turn
OFF the AC heater relay.
Any time relay K2 is turned ON, AC voltage is applied to
the AC heater via the now closed K2-contacts. Any time AC
voltage is applied to the AC heater, an AC current is produced.
Theory of Operation - Manual AC Mode
Theory of Operation - cont’d.
