DRAFT
NOT FOR PUBLIC RELEASE
32
www.norcold.com/cda
N500/N510 Models
Refrigerator Service Manual
COOLING UNIT
Gradual Decrease in Cooling Efficiency
A gradual decrease in cooling efficiency can be caused
by the following factors:
T Ventilation obstruction.
T Heat source failure.
T Off-level operation.
T Lack of service or maintenance.
T Inadequate repairs.
T Unauthorized field modifications.
T Cooling unit failure.
Note that a gradual decrease in cooling efficiency is not
always an indication of cooling unit failure. If any of
these factors exist and are not corrected, a replacement
cooling unit will also perform inefficiently or fail.
Step-by-step troubleshooting is the best approach when
dealing with a gradual decrease in cooling. It is
important to consider that the cooling unit is working,
though not efficiently. A Cooling System Diagnostic
Flowchart can be found on pages 34 and 35. The
cooling unit must reach peak efficiency before
troubleshooting can take place. It takes an average of
four hours for the refrigerant to reach peak efficiency.
This time frame depends on ambient air temperature.
Additionally, ambient air temperature plays a significant
role if the unit was not installed correctly. Incorrect
installation leads to poor ventilation, which in turn
relates to poor cooling performance.
The unit's service and maintenance history should also
be considered when checking a cooling unit for poor
cooling performance. The service history and the scope
of service work performed may lead directly to the
cause and resolution of a cooling problem.
Cooling Monitoring - N510 Units Only
Cooling Monitoring monitors the fin assembly
temperature through the thermistor. This control is
activated when the refrigerator is turned on and when
the fin assembly temperature has rises above 40° F.
When the fin temperature is above 40° F and a change
in cooling is not detected in a specific amount of time,
the refrigeration heat sources are turned off. Cooling
Monitoring will not activate if:
T The fin assembly temperature stays below 40° F.
T If the thermistor is disconnected, open, or shorted.
T If the fresh food compartment door is sensed open
(resampling starts when door closes).
T The ac heater is open.
T AC voltage is low.
T Frost management is active.
Description
The cooling unit is a self-contained gravity flow
absorption refrigeration system. The refrigerant charge
is a solution of water, ammonia, sodium hydroxide, and
sodium chromate (a corrosion inhibitor). Refrigeration is
accomplished by applying heat energy and venting the
heat extracted from the freezer and fresh food cabinet
while maintaining the unit leveled.
Heat Absorption
The refrigerant transfers the heat from the freezer and
the food cabinet to the absorber coils. At the absorber
coils the metal surface absorbs the heat and air flow
over the external surfaces of the coils carries away the
heat. A thermal air current is created by the rising hot air
and flows out of the enclosure through the roof exhaust
vent or sidewall exhaust vent (depending on
installation). The flowing air mass passes over the
surface of the condenser fins where it absorbs heat
transferred from the ammonia vapors flowing through
the condenser.
The thermal airflow process creates a "chimney effect."
The fresh air drafted by the chimney effect through the
intake vent removes rejected heat, supports
combustion, and expels the exhaust gases produced by
the combustion process. Any obstruction, restriction, or
modification to vents or the enclosure will affect the
cooling cycle. Poor cooling unit performance may be
due to:
T Loose insulation interfering with the ventilation
process.
T Construction material or debris left in the enclosure.
T Insect screening covering vents.
T Plastic sheeting covering vents.
T Items stored in the enclosure.
T Modifications to vents or enclosure.
T No roof or sidewall exhaust vent opening.
Information pertaining to ventilation and enclosure
requirements appear on pages 21 and 22.
Leveled Operation
The circulation of the refrigerant through the cooling unit
is accomplished by gravity flow; therefore, the
refrigerator must be operated leveled. Off-level
operation will effect the flow of the refrigerant through
the cooling system. The maximum off-level operation
limits are:
T 3 degrees from side-to-side.
T 6 degrees from front-to-back.
Exceeding the maximum off-level limits can
permanently damage the cooling unit.
The cooling unit or its performance are not affected
when the vehicle is in motion.
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