Thermo Scientific Harris Ultra-Low Temperature Freezers
Installation and Operation
6
5.2.5 Alarm Test (Harris DLT and SLT Freezers)
To test the cold and warm alarms, complete the following steps:
1. Press and hold the Alarm Test pad. The digital temperature
display indicates rising temperature. When the temperature
reaches the warm alarm value, the alarm sounds.
Note:
The temperature of the refrigerated space does not
change during this procedure. Only the sensor is heated.
2. Release the Alarm Test pad, the sensor and display return to
cabinet temperature in a few minutes.
You can press the Alarm Reset pad to silence the alarm but the
alarm will ring back in five to seven minutes. You can silence the
alarm in this manner as many times as necessary until the sensor
cools below the warm alarm temperature. The alarm quits
automatically when the sensor cools below the warm alarm
value.
Note:
There is a limit on the alarm test feature. The alarm test
will not commence if the warm alarm set point is more
than 15 degrees warmer than the operating temperature
set point.
6 Backup System (Optional)
When you purchase a built-in CO
2
or LN
2
optional backup
system for the freezer, the backup system control panel is located
behind a hinged panel adjacent to the grill (refer to Figure 4).
Note:
Always purchase the cylinders which are equipped with
siphon tubes for withdrawing liquid from the bottom of
the cylinder. CO
2
cylinders must be kept at room
temperature to function properly. LN
2
bottles are
functional at any reasonable temperature.
Use the panel below to set the backup initiation temperature,
usually 10 to 15×C warmer than the operating set point.
Figure 4. Control Panel for Optional
Built-In Backup System
TEMPERATURE ºC
PUSH
TO SET
SET POINT
ADJUST
POWER
OFF
ON
Power
Switch
Temperature Control
Set Point Screw
Temperature Control
Set Button
Digital Temperature
Display
Note:
Harris ELT Series units and DLT chest models use
free-standing, field installed Backup Systems.
6.1 CO
2
and LN
2
Precautions
Observe the following precautions when using liquid CO
2
and
LN
2
backup systems.
WARNING!
If a CO
2
or LN
2
cylinder falls and a
valve is knocked off, the cylinder becomes a deadly
and completely unguided missile. Transport the
cylinders in a handtruck or cart with secure chain ties
for the cylinder. After cylinders are connected to the
equipment, securely attach them with chains to a
solid, stationary object such as a building column.
WARNING!
CO
2
and LN
2
liquids are non-poisonous
but are very cold and will burn unprotected skin.
Always wear protective eyewear and clothing when
changing cylinders or working on the piping systems
attached to an active source of liquid refrigerant.
WARNING!
The gases produced by evaporation of
CO
2
or LN
2
are non-poisonous but displace the
oxygen in a confined space and can cause
asphyxiation.
Do not store the cylinders in
subsurface or enclosed areas
.
CAUTION!
When closing the cylinder valve, make
sure that the injection solenoid is energized to allow all
the liquid to bleed off instead of being trapped in the
supply tubing. Failure to do this results in activation of
the pressure relief device, which could damage the
freezer and requires replacing if it is activated.
CAUTION!
For chest and upright models ordered
with factory installed built-in backup systems, the flow
of liquid CO
2
or LN
2
will be discontinued if the door or
lid is opened during operation of the backup system.
For units operated with free-standing, field installed
type backup system, the flow of liquid CO
2
or LN
2
will
be discontinued upon door or lid opening
only
if the
switch provided with the free-standing package is
installed on the freezer.
6.2 Installation
Field installed systems are supplied with complete installation
and operating instructions. If your system is factory installed, the
freezer is shipped with a coiled length of tubing to connect the
freezer to the bottles:
•
3/8 in. OD copper tubing for connection to the CO
2
supply.
•
5/8 in. OD copper tubing covered with Armaflex
™
insulating
tubing for connection to the LN
2
supply.
Straighten the coiled tubing and connect one end to the labeled
connection on the freezer and the other end to the supply bottle or
building supply fitting.
