SCAD SensiStat User manual

© 2009 SCAD Technologies LLC •www.scadtech.com Page 1
SensiStat™ Energy Saver
Refrigeration Controller
Revision 2.05
(Applies to SensiStat Revision 2.x products)
HOW IT WORKS.........................................1
INSTALLATION..........................................2
OPERATION...............................................4
CUSTOMIZATION / PROGRAMMING........7
TROUBLE SHOOTING.............................12
MY SENSISTAT CUSTOM SETTINGS..... 14
FACEPLATE TEMPLATE.........................15
The SCAD SensiStat™ Energy Saver refrigeration controller works with your 12 or 24-volt
holding (aka holdover) plate refrigeration system and reduces your battery usage by:
• Providing extremely precise thermal control thus reducing excess running of your
refrigeration compressor
• Automatically utilizing available “excess” power while your batteries are charging.
This reduces the amount of battery energy used each day for refrigeration and
saves you hours of battery charging time each week. This savings translates to
real dollars as you will use less fuel for battery charging and reduce wear-and-
tear on your engine or generator.
NOTE: If you connect power to your SensiStat while the temperature probes are above 16
degrees F, after two minutes, the high temperature alarm will sound and "E04" will be
displayed. This is normal and correct behavior. To mute the beeping, press the PRG key
briefly. To adjust the high temperature alarm threshold, delay, or to disable the high
temperature alarm, refer to the high temperature alarm section of this manual.
HOW IT WORKS
A typical thermostat turns on your refrigeration compressor to freeze holding plates solid.
The plates are then allowed to defrost to a temperature approximately 8oF higher before
the compressor is turned on again and the plates are refrozen. The difference between
the freezing temperature and the “defrosted” temperature is known as hysteresis or
differential. This is the most energy efficient method and the more precise the control, the
more efficient the system and the more likely your ice cream will remain solid. The
SensiStat refrigeration controller, with a resolution of 1/10oF provides unparalleled
precision of control. What’s more, the SensiStat comes with temperature sensors to allow
you to monitor and display both the holding plate temperature and refrigeration box
temperature.
Normal thermostats also do not take advantage of randomly available “free” or “excess”
power provided whenever your engine or generator are running and charging your
batteries. Since batteries can only charge so fast, there is normally plenty of extra
generation capacity available to run your refrigeration system “for free”, that is using
energy without depleting your batteries. When the SensiStat refrigeration controller
detects charging level voltages, it closes down the hysteresis to only 1oF and uses the
available free power to “top-up” the freeze on your holding plates. For example, when you
are motoring into an anchorage at the end of the day, the SensiStat will automatically run
your refrigeration compressor while your engine is running and save you all the battery

© 2009 SCAD Technologies LLC •www.scadtech.com Page 2
energy that would have been used later in the evening running the refrigeration
compressor for the same amount of time directly off the batteries.
You can also tell the SensiStat refrigeration controller to ignore extra power (such as while
plugged in a dock) or to force a freezing of the holding plates for up to 60 minutes.
Additionally, the SensiStat detects excess voltages which might damage your refrigeration
system, alerts you, and does not over-ride the differential when excess voltages are
present.
Your SensiStat also includes an over-temperature alarm. If the plate temperature reaches
16 oF over the set point for more than two minutes, a mutable alarm will sound. You can
change the settings and behavior of the over-temperature alarm and even disable it.
Finally, although the factory settings will work for most sailors, you can custom program
the voltage threshold at which the SensiStat overrides the differential. You can also set
the holding plate freezing temperature, the normal and override differentials, the displayed
temperature scale (Fahrenheit or Centigrade), and whether the holding plate or box
temperature is displayed by default.
INSTALLATION
The SensiStat refrigeration controller simply replaces your current thermostat, switch, or
timer. Find a convenient place to mount your SensiStat and cut the appropriate hole using
the template found at the end of this manual.
The SensiStat has removable terminal connectors to make the wiring task easier. Note
that the screws of the connectors face down. Do not force the connectors into place. If
you have to push hard, you have the connectors mis-located – double-check the color of
the connector and its position. (Green connector goes to green connector, orange to
orange).
We have also painted reference colors on each of the connectors to help make the wiring
easier. Here are the color codes (see also Figure 1):
Red: plus voltage (+12V or +24V)
Green: ground
White: common leads of temperature probes
Yellow: holding plate temperature probe lead
Blue: box temperature probe lead
Purple: control line to your refrigeration system
If your current thermostat does not have a ground wire (a third wire), you need to add one.
This wire is typically color-coded black and should tie back eventually to the battery’s
negative terminal. Most thermostats and all switches or timers use two wires. One is
positive voltage wire (+12 volts on a 12V boat or +24 volts on a 24 volt boat) when the
refrigeration circuit breaker is turned on, the other returns to the refrigeration system to
turn on the compressor. By disconnecting both of these wires from your current
thermostat, switch, or timer you can determine which is the positive voltage wire by testing
each in turn with either a light bulb or a voltmeter. One lead of your test bulb or voltmeter
would go to ground (battery negative) and the other to the wire being tested. The wire,
which lights the bulb (when the refrigeration circuit breaker is turned on), or shows around
+12 or +24 volts on your voltmeter, is the +12V/+24V lead. You may want to mark it with
some red tape. TURN OFF POWER TO THE REFRIGERATION SYSTEM until all
connections to the SensiStat are completed. Connect the +12V/+24V wire to terminals 1

© 2009 SCAD Technologies LLC •www.scadtech.com Page 3
and 6 of the SensiStat, per the illustration below. The other wire connects to terminal 3
per the illustration below.
If you have a 120V AC or 220V AC refrigeration system, it is likely that the switched line
will be switching that high voltage. If this is the case, terminal 1 will not be connected to
the lower DC voltage of your boat (12V or 24V) and the red jumper wire provided that
connects between terminals 1 and 6 should be removed and disposed of. The two wires
that connected to your old thermostat should be connected to terminals 1 and 3.
123 6789101112
compressor (purple)
+12V or +24V * (red)
ground (green)
box sensor (blue)
plate sensor (yellow)
sensor common (white)
SensiStat
Plugs
+12V or +24V * (red)
CNONC
not used not used not used
* If you have a 120VAC or 220VAC refrigeration
system, please refer to special instructions above.
Figure 1
Your new SensiStat includes two temperature sensors. They are both the same, but each
is color coded to help you trace which is used for the box temperature and which is used
for the holding plate temperature. The temperature sensors have been calibrated and
matched to your SensiStat. You must match the blue and yellow coded wires to the
connectors on the SensiStat or you will defeat the calibration.
It is critical that the holding plate temperature sensor be placed in intimate contact with the
holding plate as close as possible to the point where its coolant line returns to the
compressor. If you have multiple plates in series, place the sensor on the last plate. You
can tell which line is the return line by feeling the lines shortly after starting the
compressor. The warmer line is the return line. There will typically be frost on the source
line and none on the return line.
Some holding plates have wells specifically intended to hold the temperature sensor. If
your plates have such as well, insert the sensor into the well. You can seal the hole and
hold the sensor in with a bit of silicon sealer, putty, chewing gum, or the like.
If your holding plates do not have a temperature sensor well, you will need to tape the
sensor to the holding plate. You should be able to tell where the cooling coils run within
the holding plate by observing a light layer of frost on the holding plate. Avoid placing the
sensor directly over the coil. The silver tape provided with your SensiStat will adhere well
to a holding plate BUT YOU MUST ONLY APPLY THE TAPE WHEN THE PLATE IS AT
ROOM TEMPERATURE. The tape will not stick at all if applied to a cold holding plate. If
applied to a warm holding plate, the tape will bond well and not come off when the plate is

© 2009 SCAD Technologies LLC •www.scadtech.com Page 4
frozen. Smooth any air bubbles out from under the tape. It is best to have the wire lead
downward so moisture will not collect under the tape.
The temperature sensor for monitoring the icebox temperature should be mounted away
from the plates and may be taped to the wall of the box. Route the wires in such a
manner that they will not be easily snagged or caught on food items.
The temperature sensor wires may be shortened or just coiled up behind the thermostat
with the provided wire tie. Should you shorten the temperature sensor wires, you may
replace the color-coded heat shrink tubing with the short pieces provided. Use only warm
air to shrink the tubing, such as well above a candle; do not pass the tubing through an
open flame.
One conductor from each temperature sensor is connected to terminal 10 of the
SensiStat. These are the white coded wires. The second conductor from the holding
plate sensor (yellow) is connected to terminal 8. The second conductor from the box
temperature sensor (blue) is connected to terminal 9 on the SensiStat. DO NOT connect
anything to terminals 11 or 12.
OPERATION
Components of the SensiStat refrigeration controller: The SensiStat consists of an
industry standard digital thermostat manufactured by the world leader in thermostatic
controls, Carel, married to a SCAD-designed microprocessor-based daughter board
mounted within the thermostat. The thermostat is custom programmed to respond to the
daughter board’s commands to override its differential. The daughter board recognizes
the voltage of the battery system of your boat and decides when to override the
differential. It also monitors over voltage conditions, allows you to manually override the
differential for a period of 60 minutes, to disable the override function, or to change the
threshold voltage at which the override function is enabled.
You control the functions of the daughter board via the function button and receive
feedback from the daughter board via the function LED.
You may change the settings of the thermostat, including the holding plate freezing
temperature, differentials, and display units (Fahrenheit or Centigrade) using the buttons
on the thermostat.
Function
Button
Function
LED
Figure 2: Front Panel of SensiStat Energy Saver

© 2009 SCAD Technologies LLC •www.scadtech.com Page 5
Icons you may see:
(small) 1 When on it means the thermostat is asking the compressor to run. When
flashing, the thermostat wants the compressor to run but compressor
protection is enabled. (To protect your refrigeration compressor, we only allow
it to start once every 5 minutes).
Alarm: Flashes when an alarm is active
• E01 = Probe 1 fault (usually means it is not properly connected)
• E02 = Probe 2 fault (usually means it is not properly connected)
• E04 = High temperature alarm
• E05 = Low temperature alarm (you should not see this alarm unless your
set point temperatures are set to unusual values)
Direct Mode Operating: When on it means the thermostat is asking the
compressor to run.
Prg
mute
• If pressed for more than 5 seconds, accesses the menu for setting type P
parameters;
• Mutes the audible alarm buzzer;
• When editing the parameters, pressed for 5 seconds, permanently saves
new values for the parameters;
• If pressed for more than 5 seconds together with Set, accesses the menu
for setting the type C parameters (configuration);
• If pressed for more than 5 seconds at startup, activates the procedure for
loading the default parameters.
S
(Up)
• Increases the value of the set point or any other selected parameter
T
(Down) • Decreases the value of the set point or any other selected parameter.
• In normal operation accesses the display of the second probe and digital
inputs.
Set • If pressed for more than 1 second displays and/or sets the set point;
• If pressed for more than 5 seconds together with Prg/mute, access the
menu for setting the type C parameters (configuration).
Power-on self-test: Each time the SensiStat refrigeration controller receives power, it
conducts a self-test and determines the voltage of your batteries. The indicator LED will
display a string of 8 rapid flashes, pause, flash the revision code of the firmware (such as
two long, and one short flashes for revision 2.1), pause, and then display another string of
8 rapid flashes. At this point you are assured the system is working correctly. The
thermostat display will conduct a self-test also. All of the elements of the display will light
briefly. It is very important that you do not press any buttons during the self-test or you
may put the thermostat into an undesired diagnostic mode. Should this happen, just
remove power from your SensiStat, wait a few seconds, and return power to your
SensiStat.
Factory Settings: The SensiStat refrigeration control comes from the factory set for most
marine freezer holding plate systems with the freezing point set to 0oF and the differential
set to 8oF. Consult your refrigeration manual or manufacturer to determine their preferred
settings. Refrigerator-only holding plates typically freeze at 24oF.
Normal Thermostat Mode: When battery voltages are below charging voltage, the
SensiStat will operate as a very precise thermostat. When demanding the compressor to
run, the “direct” LED will flash slowly. By default, the temperature of the icebox is
D

© 2009 SCAD Technologies LLC •www.scadtech.com Page 6
displayed. (See “Customization” below if you prefer the holding plate temperature to be
displayed by default).
“Free Power” Mode: The SensiStat will override the differential, down to 1oF when
“Free Power” is available for 30 seconds. “Free Power” means charging voltage
exceeding 14 volts on a 12-volt system or 28 volts on a 24-volt system. The SensiStat
automatically determines if you have a 12 or 24-volt system each time it is turned on.
The SensiStat indicator LED flashes (1/2 second on - 1/2 second off) when “Free Power”
first becomes available. After 30 seconds, the LED will light continuously and the
differential will be overridden. When the SensiStat is asking the compressor to run, the
symbol
D
“Direct” and a small “1” will be displayed.
Over Voltage Alert: Should the SensiStat detect an over voltage condition, the Free
Power and Manual Override modes will be temporarily disabled and the function LED will
illuminate. The thermostat will otherwise function normally during an over voltage alert.
The over voltage level is factory set at 15 volts for 12 volt systems and 30 volts for 24 volt
systems.
Manual Override Mode: Manual override mode allows you to force a “topping-up” of your
holding plates. When in manual override mode, the differential is overridden, unless an
over-voltage condition is detected. The manual override mode resets automatically after
approximately 60 minutes.
• To start the manual override mode, briefly press the function button. The
function LED will flash once per second during manual override mode. The
“direct” LED will flash indicating the thermostat is asking your refrigeration
compressor to run. The “direct” LED will continue to flash until the holding plate
is re-frozen or 60 minutes have elapsed.
• To cease the manual override mode, briefly press the function. The function LED
will cease flashing once per second. The SensiStat will return to normal
operation. If “Free Power” is available, the SensiStat will respond accordingly.
Disabled Mode: You may choose to prevent your SensiStat from responding to “Free
Power”. You may want to do this for example, when you are plugged in at a dock. The
thermostat will continue to operate normally. Only “Free Power” mode will be defeated
while in disabled mode.
• To enter disabled mode, press and hold the function button until one string of
rapid flashes is displayed, then release the function button. The SensiStat will
enter disabled mode. The function LED will flash briefly once every 15 seconds
or so. This brief occasional flashing is just a reminder to you that the SensiStat is
in disabled mode.
• To exit disabled mode, press and hold the function button until one string of rapid
flashes is displayed, then release the function button. The SensiStat will exit
disabled mode and resume normal operation.
Compressor Protection: The SensiStat provides protection against short cycling your
refrigeration compressor. Once the SensiStat turns off your compressor, it will not be
turned on again for at least 5 minutes.
High Temperature Alarm: The SensiStat is now equipped with an audible high
temperature alarm. From the factory, the alarm is set in “relative mode” and will alarm

© 2009 SCAD Technologies LLC •www.scadtech.com Page 7
when the plate temperature exceeds the set point by 16 deg F for two minutes. You may
change the relative offset or set an “absolute” high temperature alarm. (See
customization/programming section).
A high temperature alarm will display . The current probe temperature and “E04”
will flash on the display and the SensiStat will beep. To mute the beeping, press the
Prg/mute key briefly.
CUSTOMIZATION / PROGRAMMING
If the factory settings do not meet your needs, you may easily change the settings.
Please do not attempt to change any setting other than those outlined below. Changing
other setting may make the unit behave in unpredictable ways and could void your
warranty.
“P” settings can be changed by entering programming mode or advanced programming
mode. “C” settings can only be changed using advanced programming mode.
Changing “P” Parameter Settings – Entering Programming Mode:
1. To enter programming mode, press and hold the PRG key for 5 seconds.
2. The display will show “P1”.
3. Release the PRG key.
4. Use the
S(Up) and T(Down) keys to reach the desired “P” parameter you wish
to set.
5. Press the SET key briefly to select the “P” parameter.
6. The current setting of the selected “P” parameter will be displayed.
7. To change the parameter value, press either the S(Up) and T(Down) keys until
you reach the desired value.
8. Press the SET key briefly to confirm the new value. (If you do not wish to make a
change, pressing SET will preserve the current setting).
9. You may select other “P” parameters by repeating steps 4 through 8 above or
exit programming mode by holding the PRG key for several seconds until the
normal mode is displayed (temperature display).
NOTE: If you do not exit the programming mode by holding down the PRG key, your
new settings will not be saved and your prior settings will be restored. If you remain
in programming mode too long without doing anything, the display will flash for
several seconds and then return to normal mode. NONE of your changes will be
saved.
Changing “C” and “P” Parameter Settings - Entering Advanced Programming
Mode:
To change the settings of the “C’” and “P” parameters you must first enter advanced
programming mode. Care should be taken to first plan and write down your setting
changes before entering advanced programming mode. Near the end of this manual you
will find a worksheet entitled “My SensiStat Custom Settings”. This shows the factory
settings and provides a worksheet for recording your changes to those settings. Again, as
we cannot emphasize this enough, there are dozens of “C” and “P” parameters - do not
change “C” or “P” parameter values other than those specified in the instructions below.
1. Press and hold the PRG and SET keys down for 5 seconds.
2. The display will show “0”.
3. Release the PRG and SET keys.
4. Use the
S(Up) and T(Down) keys to change the display to show “77”.

© 2009 SCAD Technologies LLC •www.scadtech.com Page 8
5. Briefly press the SET key.
6. The display will show “C0”. You are now in advanced programming mode and
can alter the “C” and “P” parameter settings.
7. Use the S(Up) and T(Down) keys to change the display to select the “C” or “P”
parameter you wish to change.
8. Briefly press the SET key to program the selected parameter.
9. The current setting for the selected “C” or “P” parameter will be shown. If you
wish to change the displayed unit setting, use the S(Up) and T(Down) key to
change the value.
10. Briefly press the SET key to lock-in your selection. (If you do not wish to make a
change, pressing SET will preserve the current setting).
11. Hold the PRG key for several seconds to exit the programming mode until the
normal mode is displayed (temperature display).
NOTE: If you do not exit the advanced programming mode by holding down the
PRG key, your new settings will not be saved and your prior settings will be
restored. If you remain in advanced programming mode too long without doing
anything, the display will flash for several seconds and then return to normal
mode. NONE of your changes will be saved.
To Change Displayed Units (Fahrenheit or Centigrade):
We recommend using Fahrenheit units as this provides a finer level of precision than
Centigrade. (0.1oF is a smaller unit of measurement than 0.1oC).
NOTE: After changing the displayed units, your SensiStat will automatically convert all
temperature related settings to the new scale. (For example a value set to 32.0oF will be
converted to 0.0oC). It is nonetheless suggested that you confirm that all of the settings
are now at the values you intend.
Caution: This procedure will place the thermostat in advanced programming mode. DO
NOT CHANGE ANY SETTINGS OTHER THAN C18 with this procedure. Doing so could
create unpredictable behavior, render your unit inoperable, and void your warranty.
1. Enter advanced programming mode following the instructions above.
2. Select parameter “C18”
3. Change “C18” value to 1 for oF or to 0 for oC
4. Briefly press the SET key to lock-in your selection. (If you do not wish to make a
change, pressing SET will preserve the current setting).
5. Hold the PRG key for several seconds mode until the normal mode is displayed
(temperature display) to exit the programming mode.
High temperature alarm:
• Relative mode: Relative mode is the default for the high temperature alarm. Relative
mode sets high temperature alarm value relative to the set point. The number of
degrees of this offset is set to 16 by default. So, since the default set point is 0
degrees, with a relative alarm offset of 16 degrees, if the plate temperature reaches
16 degrees F, and this temperature is maintained for 2 minutes (default setting), the
SensiStat will beep, the SensiStat will display and the current probe temperature
and “E04” will flash on the display. To mute the beeping, press the Prg/mute key
briefly.
We like and recommend relative mode because you don’t have to change the alarm
settings if you change the set point. You may change the relative offset by altering

© 2009 SCAD Technologies LLC •www.scadtech.com Page 9
the value of parameter P26 in programming mode. For relative mode, P25 and P29
must be set to 0. Use programming mode, as explained above to change these
settings.
• Absolute mode: Alternatively you can set an absolute high temperature alarm. That
is, you can set a particular temperature at which the alarm is activated. First you
must change the alarm mode to absolute by changing P29 to 1. Next you must
change P25 to -50. Finally you can set P26 to the temperature at which you wish the
alarm to occur.
• High temperature alarm delay:By default, the high temperature must be maintained
for two minutes before the alarm sounds. You may change this value (in minutes) by
changing P28.
• To disable the beeper: Change the value of C53 to 1 in programming mode. To re-
enable the beeper, change the value of C53 back to 0.
To change default temperature sensor display:
Your SensiStat by default displays the temperature sensed by the icebox temperature
sensor (probe 2, also known as “b2”). Probe 1, also known as “b1”, is the probe on your
holding plate and the one that controls the behavior of the SensiStat. By pressing the T
(Down) key, and then using the T(Down) or S(Up) keys you can scroll between display
choices. This can be a bit confusing, so experiment a bit to get the feel of it. What you
will see is an alternating display, first what is going to be displayed, like “b1” and then the
value of that probe. The alternating will continue until you lock in your choice by holding
down the Set button for a few seconds. You will also see “din1” and “din2” as choices for
display. Please just ignore these choices.
To display or set the freezing temperature:
1. To enter the set point programming mode, press and hold the SET key for 5
seconds.
2. The display will show “St1”, the variable for the freezing temperature for normal
operation.
3. Release the SET key. The display will now show the current setting for St1.
(Factory default is 0oF).
4. If you wish to change this value, press either the S(Up) and T(Down) keys until
you reach the new desired value.
5. Press the SET key briefly to confirm the current or new value of St1.
6. The display will show “St2”. This is the variable for the freezing temperature for
override mode. This value should be set to the same value as St1.
7. The value of St2 will be displayed. (Factory default is 0oF).
8. If you wish to change this value, press either the S(Up) and T(Down) until you
reach the new desired value.
9. Press the SET key briefly to confirm the current or new value of St2.
10. The SensiStat will return to its normal display mode.
To display or set the differential settings:
Generally, there is no need to change the differential settings unless your refrigeration
manufacturer specifies a different differential. Remember, the override differential is
critical for the “Free Power” mode to operate correctly. Avoid changing the “P2” value
unless you are certain you know why you are changing it.
1. Enter programming mode following the instructions above.
2. Select parameter “P1” (differential for normal operation) or “P2” mode (differential
for override operation).
3. After changing these values, exit programming mode by holding the PRG key for
several seconds until the normal display (temperature display) appears.

© 2009 SCAD Technologies LLC •www.scadtech.com Page 10
To Display or Change the “Free Power” Threshold Voltage:
The voltage at which the “Free Power” mode will be engaged is factory set to 14 volts for
12 volt systems and 28 volts for 24 volts systems. The ranges of settings are:
• For 12-volt systems: 13.0 volts to 14.5 volts in 0.1-volt steps.
• For 24-volt systems: 26.0 volts to 29.0 volts in 0.2-volt steps.
You may only change the value for the voltage at which your SensiStat is currently
operating. That is, if you are on a 12-volt boat, you can only change the settings for 12
volts systems.
1. Press and hold the function button.
2. Release the function button only after two strings of rapid flashes are displayed.
(but before the third string of rapid flashes is displayed)
3. The function LED will begin to flash out voltage setting options in a Morse code-
like fashion. The selections will be displayed as follows:
4. If you wish to only display the value of the current threshold voltage setting your
SensiStat is using, instead of changing the setting, you may do this by now
pressing and holding the function button until a long string of flashes is displayed.
As soon as the long string of flashes is displayed, release the function button.
After a brief pause, the function LED will flash out the current threshold voltage
setting, for example: “- ….”, one long, four shorts, for the factory default for 12
volt systems, 14.0 volts. The SensiStat will then exit the threshold voltage
programming mode, retaining the current setting, and resuming normal
operation. If you now wish to change the value of the threshold voltage, return to
step 1 above, and skip step 4.
12 Volt Systems
Volts Long Flash Short Flash
13.0 1 3
13.1 3 1
13.2 3 2
13.3 3 3
13.4 3 4
13.5 3 5
13.6 3 6
13.7 3 7
13.8 3 8
13.9 3 9
14.0 1 4
14.1 4 1
14.2 4 2
14.3 4 3
14.4 4 4
14.5 4 5
24 Volt Systems
Volts Long Flash Short Flash
26.0 2 6
26.2 6 2
26.4 6 4
26.6 6 6
26.8 6 8
27.0 2 7
27.2 6 2
27.4 6 4
27.6 6 6
27.8 6 8
28.0 2 8
28.2 8 2
28.4 8 4
28.6 8 6
28.8 8 8
29.0 2 9