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

A positive defrost is required to remove frost from the coil. This is accomplished by energizing
heaters positioned on the coil surface. The time clock, refer to Figure 1, is factory set to allow four
defrosts per day. Note: Setting the correct time of day will be required to maintain these
defrost periods.
When 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 10°C, 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 -4°C.
Adjustments
The timer switch is located behind the lower front panel. Remove the retainer screw and move the
timer forward to allow for adjustment.
1. Time clock adjustments:
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 the drawing of the time clock, 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 at 2:00 a.m., 8:00 a.m., 2:00
p.m., and at 8:00 p.m. The four settings should
provide adequate defrosting for even the most
heavily used system. 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. If
experience shows that the four set defrost periods
are more than necessary, one or more of the knurled
setscrews may be removed. At least one of the
knurled setscrews must be located on the
large lower dial at all times. Figure 1
Fail Safe Feature - 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 is factory set at 30 minutes, indicating that the system will
revert to cooling thirty minutes after a normal defrost cycle began should a malfunction occur.
The fail-safe feature is a safety mechanism and should never be used to control the length of the
defrost period. This feature is provided to protect the contents of the freezer from damage
should the system fail to revert to the cooling cycle because of mechanical difficulties. No
adjustment of this device should ever be necessary. Lengthening the fail-safe time will not
lengthen the defrost cycle.
2. Cold control adjustment - To increase or decrease the internal cabinet temperature, rotate
the cold control, located on the unit cooler, to the desired setting.
Caution: If the cabinet's door(s) remains open for too long it could cause excessive frost to build up
on the evaporator causing airflow through the coil to be restricted and to not properly defrost.