Manual Lp Gas Mode; Manual Dc Mode (3-Way Models Only) - Norcold NX61 Service Manual

Theory of Operation - cont'd.
This AC current is measured by the power board and its value
is passed on to the optical display board. The optical display
board determines if the AC current is or is not within the
specifi ed limitations. Should the current fall below ½ ampere,
the optical display board will display the appropriate AC current
related fault.
• NX61 / NX81 = Power ON indicator light fl ashes
RED once, OFF for 5-seconds, repeats
• NX64 / NX84 = "AC HE" with audible alarm/beeper
• NXA64 / NXA84 = "AC HE" with audible alarm/
beeper

Manual LP Gas Mode

To operate in the Manual LP Gas mode the optical display
must be placed to operate in this mode. Once done so, the
refrigerator will cool via the LP Gas mode and ONLY the
LP Gas mode. While in the LP gas mode the refrigerators
electronic controls will function as follows:
The power board is responsible for:
• Measuring the resistance value of the thermistor
• Determining the presence of a fl ame
• Turning ON/OFF the gas valve output
• Turning ON/OFF the igniter output
• Communicating with the Optical Display Board
The optical display board is responsible for:
• Deciding if the thermistor value is above or below
preset temperature range cut-in/cut-out values
• Deciding when to turn ON and OFF the gas valve
• Communicating with the Power Board
Theory of Operation - Manual LP Gas Mode
The power board 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 the optical display will request the power board to
turn ON the gas valve relay (K1) and high voltage transformer
(T1) outputs.
Anytime relay K1 is turned ON, 12VDC passes through the
now closed K1 contacts to terminal P1-10 of the power board
and out to the gas valve solenoid, energizing the gas valve.
With the gas valve energized LP gas fl ows out to the burner
tube. Simultaneously, energy pulses from the high voltage
transformer (T1) are carried out to the burner via the spark
sense electrode wire. As the energy pulses reach the end of
the electrode they jump across the gap between the electrode
and the burner creating sparks. The sparks ignite the LP gas
and a fl ame is established. Via the fl ame rectifi cation process
a signal is then sent back to the power board through the
spark sense electrode wire letting the power board know there
is a fl ame present.
Refrigerator Service Manual
Knowing a fl ame is present; the power board deactivates
the spark output. At the same time; the power board
communicates to the display letting it know a fl ame is now
present. When the thermistor value reaches a particular
cut-out value the optical display will request the power board
to turn OFF the gas valve output, allowing the fl ame to
extinguish.
If for some reason the fl ame goes away while there is a call
for cooling, at the request of the optical display board, the
power board will turn the high voltage transformer back on in
an attempt to re-ignite the propane. For safety reasons the
sparking at the burner will last for a maximum of 30 seconds,
at which time the gas valve/high voltage transformer outputs
will be turned off and an error will be displayed via the optical
display indicating a gas lockout condition. To reset this gas
lockout condition the controls must be powered off/on.
• NX61 / NX81 = Power ON indicator is SOLID RED
• NX64 / NX84 = "no FL" with audible alarm/beeper
• NXA64 / NXA84 = "no FL" with audible alarm/
beeper

Manual DC Mode (3-way models only)

To operate in the Manual DC mode the optical display must be
placed to operate in this mode. Once done so, the refrigerator
will cool via the DC mode and ONLY the DC mode. While in
the DC mode the refrigerator electronic control will function as
follows:
The power board is responsible for:
• Measuring the resistance value of the thermistor
• Communicating with the Optical Display Board
• Communicating with the DC Board
The optical display board is responsible for:
• Determining if the thermistor value is above or below
preset temperature range cut-in/cut-out values
• Determining when the DC board is to turn ON/OFF the
DC heater output
• Communicating with the power board
• Communicating with the DC board
The DC board is responsible for:
• Turning ON/OFF the DC heater output
• Measuring the DC heater current
• Communicating with the Optical Display Board
• Communicating with the Power Board
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