Cooling Unit; Description; Heat Absorption; Leveled Operation - Norcold N109X Series Service Manual

COOLING uNIt

Description

The cooling unit is a self-contained gravity flow
absorption refrigeration system. The refrigerant is a
solution of water, ammonia, sodium hydroxide, and
sodium chromate (corrosion inhibitor). Refrigeration is
accomplished by applying heat energy and removing
the heat genrated in the process as well as the heat
extracted from the freezer and fresh food cabinet .

heat absorption

The refrigerant tcarries the heat removed from the
freezer and the food cabinet to the absorber coils. At
the absorber coils the metal tubes absorbs the heat
and air flow over the external surfaces of the tubes
carries away the heat. During the process a thermal air
current is created by the rising hot air as it flows out of
the enclosure through the roof exhaust vent or sidewall
exhaust vent (depending on installation). The heated air
air flows over the surface of the condenser fins where it
removes heat from the ammonia vapors flowing through
the condenser.
This thermal airflow creates a "chimney effect"by
drafting fresh air by through the intake vent. In the
process the incoming air flow supports combustion,
cools heated components and expels the gases
produced by the combustion process. Any obstruction,
restriction, or modification to vents or the enclosure will
affect tthe performance of the refrigerator. Poor cooling
performance may be also be caused by:
n Loose insulation obstruction or blocking the
ventilation process.
n Construction material or debris left in the
enclosure.
n Fine mesh insect screen covering vents.
n Plastic sheets covering vents.
n Using the enclosure as a storage compartment.
n Modifications to the intake or exhaust vents or
enclosure.
n No roof or sidewall exhaust vent opening.
Information pertaining to ventilation and enclosure
requirements appear s on page 17.

Leveled Operation

The circulation of the refrigerant through the cooling
unit is accomplished by gravity flow; therefore the
refrigerator must be operated within level requirements .
Off-level operation will effect the flow refrigerant through
the cooling system. The maximum off-level operation
limits allowable are:
n 3 degrees from side-to-side.
n 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.
Refrigerator Service Manual

Gradual Decrease in Cooling Efficiency

A gradual decrease in cooling efficiency can be caused
by the following factors:
n
Ventilation restricted or obstructed.
n
Heat source weak or failure.
n
Off-level operation.
n
Lack of service or maintenance.
n
Inadequate or unauthorized repairs.
n
Unauthorized field modifications.
n
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 32 and
33. The cooling unit must reach peak efficiency before
troubleshooting can begin. On the average it takes four
hours for the refrigerant to reach peak efficiency. This
given time depends on ambient air temperature.
Additionally, ambient air temperature plays a significant
role if the unit is not installed correctly. Incorrect
installation is usually leads to poor ventilation, which in
turn results in 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 resolve a cooling problem.

Cooling Performance Monitoring Control

The Cooling Unit Monitoring Control monitors the fin
assembly temperature through the thermistor. This
control is activated when the refrigerator is turned on or
if the fin temperature rises above 50° F (40° F in earlier
power boards). When the temperature is above 50° F
and a change in cooling is not detected in a specific
time period, monitoring control turns off the heat sources
. The Cooling Unit Monitoring Control does not activate
when:
n
The fin assembly temperature is below 50° F.
n
If the thermistor is open, shorted, or disconnected
from the circuit.
n
When the fresh food compartment door is sensed
open (continues 10 minutes after the door closed).
n
The AC heater is open.
n
AC voltage is low.
n
Frost management is active.
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N109X Models