To simplify connecting up the system, the electronic control
unit mounted on the side of the compressor is fi tted with
tab-type terminals for the positive and negative main power
supply cables, modular connectors for the temperature
sensors and the control panel cables.
The modular connectors have different sizes to prevent
incorrect connection. The electronic units contains micro-
processors with programs for slow running, speeding up the
compressor when the engine is running, battery monitoring
for high and low voltage, automatic de-frosting, water pump
control, regulating the holding plate temperature, transmitting
signals to the control panel etc.
The compressor and the electronic units fulfi l applicable radio
interference regulations (EMC) and are CE-marked.
When connected to shore power, a high quality marine
battery charger of minimum 15A output should be used. The
battery charger must always be connected to the batteries
and never direct to the refrigeration system.
Holding plate – Fig. B
The holding plate is a hermetic, stainless steel container
holding a special cooling medium, which freezes to ice when
the engine is running. The freezing point of the liquid is
normally –8°C (17°F). The holding plate is connected to the
compressor unit by a pliable, 3 meter (~10 foot) long tinned
copper pipe of 6 mm ( ¼") diameter fi tted with quick coupling
connectors. The holding plate must be fi tted as high as
possible in the refrigerator. It may be installed in any vertical
or horizontal position required and at any level above or
below that of the compressor unit.
A temperature sensor is fi tted to the rear of the holding plate.
This is to be connected to the compressor unit by the cable
and can suitably follow the same route as the connecting
pipe. This pipe, together with the compressor unit and
the holding plate, is pre-fi lled with the correct amount of
refrigerant and on no account should any attempt be made to
either shorten or lengthen the pipe. If the pipe is too long, the
excess should be made into a coil at some suitable position.
If a longer pipe is required, pre-fi lled 1.5, 2 and 2.5 metre
extension pipes are available.
A 2.5 metre (8 ft.) extension for the temperature sensor cable
is also available,
Part no. SEB 00038 AA.
Control panel – Fig. C
The control panel is
equipped with a three-way
switch, green, yellow and
red indicator lights and a
rheostat for manual tempe-
rature setting when running
on shore power or on solar
panels. The system is
off when the selector switch
is in the middle position.
Upper position is MAN.TEMP and lower position is
NORMAL.AUTO.
The control panel has a modular connector for the 4 metre
(13 ft.) control cable from the electronic unit. Should this
require extending, use the 10 metre (33 ft.) accessory control
cable instead. Part no. 39230.
The control panel is normally placed near the refrigerator.
OPERATION
The Isotherm ASU Magnum can be operated in two ways. In
NORMAL.AUTO or MAN.TEMP.
When energy saving is needed, switch to NORMAL.AUTO
working mode. Optimum refrigeration temperature is then
automatically maintained while consuming the lowest amount
of battery power possible.
When there is no need of energy saving, switch to
MAN.TEMP working mode. The automatic functions are now
partially blocked and the refrigeration temperature can be
manually adjusted. (Fig. C)
By means of the three-way switch on the panel the
refrigeration system is started, stopped and working modes
are selected. Working mode is indicated on the indicator
lights to the right of the switch. No indicator light on means
the system is off.
Operation in NORMAL.AUTO
The green light indicates that power is being supplied and the
refrigeration system is on.
When the engine is running and the voltage supply is over
13.2 (26.4) volt (measured on the compressors control unit),
the compressor starts to supply cooling energy to the holding
plate. It starts within the fi rst 30 seconds and operates fi rst at
low speed with the yellow indicator light "Economy" on and
after half a minute, the speed of the compressor increases
by 75% and the red indicator light "Freeze" comes on instead
of the yellow. This operating condition is maintained until the
holding plate is completely frozen at approx. –14°C (7°F).
This can take between 45 minutes and 2 hours depending
on box size, box insulation and ambient temperature. On
reaching this temperature, the compressor stops and the
red light goes out and only the green will remain on. When
the temperature of the holding plate rises to –10°C (14°F),
the compressor restarts to charge the holding plate and the
red light comes on again. This process is repeated a couple
of times every hour keeping the holding plate at its optimum
effi ciency level.
When the engine is stopped, the compressor also stops
shortly afterwards when the battery voltage has gone down
to 12.7 (25.4) volt. The surplus of refrigeration energy stored
in the holding plate is now used fi rst. Only when this has
been consumed does the compressor start again. The yellow
light indicates that it is now running, in the fi rs hand, at its
low "Economy" speed to top-up the holding plate only. This
working condition starts when the temperature of the holding
plate rises to -1°C (30°F) and stops when it reaches the
economy level of -6° (21°F).
Operation in MAN.TEMP
This position can be used either when shore power or
solar panels are being used or when energy saving is not
required and a higher or a lower refrigeration temperature
is desired for some reason. The automatic function is
partially blocked and the temperature can be set manually
on the rheostat – clockwise for colder and anti-clockwise for
warmer. "A" indicates the holding plate temperature point for
"Accumulation", abt. –8° (46°F).
In the MAN.TEMP working mode, the compressor starts
and runs in the fi rst hand in low speed to maintain the
temperature level selected. If the difference between chosen
and real temperature is more than 6°C, the compressor will
automatically speed up for faster cooling down. As soon as
this extra power is not needed, the compressor speed will be
reduced for lowest power consumption and to keep selected
temperature.
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