Nor-Lake General Laboratory Refrigerators & Freezers - Manual (Page 3)

Refrigerators
During the operation of refrigerator units, frost will periodically form on the coil surface. Each time
the compressor cycles "off", the evaporator fans will continue to run, which will keep the internal
temperature uniform and at the same time remove any frost build up on the coil. The water
produced will collect in the unit cooler drain pan and travel down the drain tube to the condensate
vaporizer.
Freezers
After shutting the door on freezer models, a short
amount of time must be allowed before the door
can be reopened. This is due to the tight seal
maintained between the door and the cabinet.
Waiting a few moments for the pressure to equalize
permits the door to be opened easily.
A positive defrost is required to remove frost from
the coil in freezer models. This is accomplished by
energizing heaters during the defrost cycle that are
positioned on the coil surface. The time clock is
factory set to allow four defrosts per day. Note:
Adjustment of the correct time of day will be
required to maintain these defrost periods.
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As the preset defrost time is reached, the time clock
automatically terminates the refrigeration process
by turning off the condensing unit and unit cooler
fan motors, and energizes the defrost heaters. As
the coil temperature increases, the frost begins to
melt producing water that runs down the coil to the
unit cooler drain pan and exits through the drain
tube to the vaporizer. After all the frost has been
removed and the coil temperature reaches
approximately 50°F, the defrost is terminated through the action of the defrost termination control
located on the unit cooler, and the refrigeration process resumes. In order to insure that any excess
water remaining on the coil is not sprayed into the cabinet interior, and all heat generated by the
defrost is removed, the unit cooler fans will not operate until the coil temperature reaches
approximately 25°F.
Figure 1
Time clock adjustments (Freezers)
Setting the correct time of day: To set the correct time of day simply rotate the small inner dial
counterclockwise until the correct time of day on the large dial is opposite the "time" indicator. In
referring to Figure 1, the correct time of day shown is 7:30 a.m.
Number of defrosts per day: The timer is factory set to defrost the evaporator four times a day. If
more defrosts are required, remove a knurled slotted screw from the holder, insert the screw into
the time slot on the large dial where a defrost is desired, and tighten. Insure that an equal time
exists between each defrost pin.
Defrost length adjustment: On the small, upper dial there is a pointer that is used to set a 100%
fail-safe feature. The fail-safe of the timer, refer to Figure 1, is factory set at 30 minutes. With this
feature, the defrost will terminate if a system malfunction occurs during defrost. No adjustment of
this device should ever be necessary. Lengthening the fail-safe time will not lengthen the
defrost cycle.
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