[8]
Defrosting the merchandiser: It is the function of
the evaporator coil to remove heat from the air in
the merchandiser. Combined with the heat are
varying amounts of humidity. While the heat is
being absorbed and removed by the refrigerant as it
circulates through the evaporator, the humidity
collects and freezes on the surface of the
evaporator. The amount of moisture collected and
the rate that it accumulates, will vary dependent
upon ambient air conditions, door openings, door
seal quality, and the “wetness” of the product being
loaded into the merchandiser. As ice builds up on
the surface of the evaporator’s tubing it will act as
an insulator between the air in the cabinet and the
surface of the tubing. This will slow the removal of
the heat from the cabinet by the refrigerant.
Eventually the ice build up will need to be removed
or it will defeat the function of the refrigeration
system. This ice removal is the merchandiser’s
defrost cycle. The means, and methods, of the ice
removal is dependent upon whether the
merchandiser is a “Cold Wall” model, or an “Auto-
Defrost” model.
Cold Wall Defrost Methods: The evaporator
tubing for the cold wall cabinet models is located
within the walls of the cabinet. After the cold wall
merchandiser is energized, a visual inspection of the
cabinet’s interior will reveal a serpentine frost
pattern developing on the ceiling and walls. This
frost pattern represents the configuration of the
evaporator tubing as it’s attached to the inside
surface of the cabinet. As humidity enters the
cabinet, it will collect and accumulate along this
frost-line pattern. As the frost-line expands and
builds in thickness, it will slow the heat transfer
between the cabinet walls and the evaporator
tubing. The cold wall cabinet models do not have
the design capability to self-defrost. In order to
defrost the cold wall models, the cabinet will need
to be emptied of product and disconnected from its’
power source. Defrosting then requires the entire
interior surface of the cabinet be warmed above
freezing to melt and remove the build up of ice from
the surface of the walls.
Power to the merchandiser can be turned off to the
merchandiser by merely unplugging the cabinet
from its’ power source. If the merchandiser is
equipped with a “mechanical thermostat”, power
can also be turned off to the refrigeration system by
rotating the temperature adjustment knob to its’ full
counter-clockwise position (Return the knob to its’
“Normal” position after the defrosting process is
completed, to re-energize the condensing unit). If
the cold wall cabinet has an “electronic control”,
unit power can also be turned off by use of the
ON/OFF toggle switch located on the control box of
certain cabinet models. If the toggle switch is not
present on the control box, the only means of
disconnecting power is to unplug the main power
cord at the power source. Although the electronic
control on the CW merchandiser has a defrost key
on its’ display face, this feature does not function
with the CW cabinet design and will not switch off
power to the run circuit if pressed.
With the merchandiser de-energized, the defrost
process can be helped along with the addition of hot
air being forced through the cabinets’ door opening
with the use of a hot air gun, or a small space
heater. As the ice build up softens, a plastic ice
scraper may be utilized to aid in removing ice from
the cabinet walls. Avoid the use of metal ice
scrapers or ice picks as these tools may
inadvertently penetrate through the wall of the
cabinet and puncture the evaporator tube, causing
irreparable damage.
A floor drain is present in most merchandiser
models. For outdoor models, the floor drain plug
could be removed to allow the water, generated by
the defrost process, to drain to the ground. If
draining to the ground is not desirable or if the
merchandiser is located indoors, the water
generated by the defrost process may be removed
with the use of a “wet-vac” and disposed of.
It’s suggested that some of the time allocated to
defrosting the cold wall cabinet may be utilized for
the cleaning of the condenser coil, as well as
inspecting the condition of wiring insulation, door
gaskets and spring-loaded hinges.
Auto-Defrost Methods: Auto-Defrost cabinet
models are equipped to be self-defrosting. These
cabinets are designed to automatically enter into
defrost mode once every four hours. During the
defrost cycle, the power to the refrigeration system
will be automatically re-directed to the defrost
circuit. This will shut down power to the
condensing unit and the evaporator fan motors and
also send power to a heat element that is attached to
the surface of the evaporator coil. The heat
generated by the element will melt the ice build up
on the evaporator coil and the resulting melt water
will drain through a tube out the back wall of the
merchandiser. On outdoor cabinet models, the melt
water will exit the drain tube directly to the ground.
