ARP Fridge Defend User manual

Fridge Defend® by ARP
Condenser
Absorber Coil
LIQUID : Water;
Ammonia; Sodium
Chromate
Refrigerated Space
Boiler Assembly
Q2
Q3
Q1
Evaporator
Cooling
Fin
Boiler
Percolator
Pump
Q1=Q2+Q3
v5.x ARP & ARP + Fan Control
Troubleshooting Guide
Please click here for Online ARP Video Operation Manual
User Web Search Engine:
Click here for Web Search before Contacting ARP Control

Terms -- Conditions & Contact Information
This manual is copyrighted © by ARPC L.L.C. 2013-2020. All rights are reserved. This manual may only be reproduced
with permission of ARPC L.L.C.. This manual is furnished for informational use only and is subject to change without
notice. This manual does not imply any commitment on the part of ARPC L.L.C. or its business partners. ARPC L.L.C.
and its business partners assume no responsibility or liability for any error or inaccuracies that may appear in this manual.
By use of this document for installation and operation of the ARP Control (Fridge Defend®), the user is agreeing to the
ARPC L.L.C. terms and conditions found in document ARPC LLC License Agreement.pdf. Also, the end user needs to
understand that the ARP Control can be turned off at any time, thereby removing the ARP Control function and reverting
to the operation of the refrigerator to its previous state. Also, the self-test functions which make the Fridge Defend an
accessory safety control may be turned off by the end user; this will defeat the 24 hour self-test. Power surges can turn off
the ARP Control just the same as any equipment in an RV, thus it is the operators responsibility to insure that the control
is functioning properly. Any ARP Control that is believed to be malfunctioning, the ARP Control must be removed from
operation and returned to ARPC L.L.C. for inspection immediately. Contact ARPC L.L.C. for shipping instructions. The
reason for return must be included in writing with the returned control; shipping is the responsibility of the end user to
and from ARPC L.L.C..
The document "ARPC LLC License Agreement.pdf" can be downloaded at web address
http://www.ARPrv.com
or, please send any request to e-mail address below, ARPC L.L.C. will supply information in a timely manner:
[email protected]
Cover Diagram
The diagram on the cover is a block diagram showing the flow of the refrigerant fluids. Q1 is
the liquid water and ammonia which enters the boiler. Within the boiler ammonia is changed
from liquid to gas Q3, and in turn forces the remaining water Q2 up the pump tube. At the top
of the pump tube the two paths for the fluids Q2 and Q3 diverge. The ammonia gas Q3 cools
the refrigerated space and then returns to the absorber coil where the water Q2 enters. Within
the absorber coil the two fluids are recombined to reconstitute the refrigerant Q1 to repeat the
cycle.

CONTENTS
SAFETY .................................................................................................................................... 1
1.1 Acronyms and Abbreviations................................................................................... 1
1.2 Hazard Information.................................................................................................... 1
1.3 Terms & Warnings Symbols..................................................................................... 1
1.4 Work Safely................................................................................................................ 1
1.5 Operation Safety........................................................................................................ 1
SETUP MODE........................................................................................................................... 1
2.1 Activate SetUp Mode................................................................................................. 1
2.2 Types of SetUp Mode Variables............................................................................... 2
2.3 SetUp Mode Button Operation ................................................................................. 2
2.4 AtO Reading............................................................................................................... 2
2.5 AtS Reading............................................................................................................... 3
2.6 AbS Process Value.................................................................................................... 3
2.7 tr Process Value ........................................................................................................ 3
2.8 OPn Process Value.................................................................................................... 4
2.9 SHt Process Value..................................................................................................... 4
2.10 SSH Process Value.................................................................................................. 4
2.11 FAn Setting .............................................................................................................. 4
2.12 SP Setting................................................................................................................. 5
2.13 OS Setting................................................................................................................ 5
2.14 Adjustment of SP or OS Settings........................................................................... 5
2.15 Temperature Units................................................................................................... 6
2.16 Set-Point Function Setting...................................................................................... 6
2.17 Defrost Setting/IEC Periodic Test .......................................................................... 7
2.18 Software Version Reading...................................................................................... 7
2.19 Serial Number Reading........................................................................................... 7
2.20 Audible Alarm (5.1 only).......................................................................................... 7
2.21 Restore ARP Defaults.............................................................................................. 7
2.22 Store Settings.......................................................................................................... 8
2.24 Exit SetUp Mode ...................................................................................................... 8
ARP ERROR MESSAGES........................................................................................................ 9
IEC Type Accessory; Redundancy; Systematic Faults & Self-Checks........................ 9
Fridge OFF; Buzzer Sounding (v5.1); Right Dot Illuminated......................................... 9
3.1 Error Message List .................................................................................................... 9
3.2 123 Numbers on Display (not an error).................................................................. 10

3.3 *Err (first dot on upper left)..................................................................................... 10
3.4 OPn Boiler Sensor................................................................................................... 10
3.5 SHt Boiler Sensor.................................................................................................... 11
3.6 -LO Boiler Sensor Reading..................................................................................... 11
3.7 *O*F*8 ....................................................................................................................... 11
3.8 *H*O*8....................................................................................................................... 11
3.9 OR (OA) Fan Temp Reading ................................................................................... 11
3.10 bAd ......................................................................................................................... 11
3.11 F4 or F5 SetUp Button Test .................................................................................. 11
3.12 E8 Error .................................................................................................................. 12
3.13 E10 Flashing when Test ARP with SetUp Button ............................................... 12
3.14 E11 Trigger Event.................................................................................................. 12
3.15 F1 MCU ADC Error Checker.................................................................................. 12
3.16 F2 at ARP Startup.................................................................................................. 12
3.17 F3 Boiler Sensor ADC Cal..................................................................................... 12
3.18 CRC Tests .............................................................................................................. 12
3.19 E12, E14, E15 MCU Tests...................................................................................... 12
3.20 ARP Reset Procedure............................................................................................ 13
INTRODUCTION to FRIDGE REPAIR.................................................................................... 13
4.1 Refrigerant ............................................................................................................... 13
4.2 Boiler Operation ...................................................................................................... 13
4.3 Boiler Pump ............................................................................................................. 13
4.4 ARP Control and the Boiler .................................................................................... 13
4.5 Burping a SPAR....................................................................................................... 13
4.6 Abnormalities and Operator Discretion................................................................. 13
HEAT SOURCES.................................................................................................................... 14
5.1 Temperature & Pressure......................................................................................... 14
5.2 Low LP Gas Pressure.............................................................................................. 14
5.3 Test Each Heat Source............................................................................................ 14
SPAR PRESSURE.................................................................................................................. 14
6.1 Low Cooling Unit Pressure..................................................................................... 14
DIAGNOSTIC VARIABLE....................................................................................................... 15
7.1 AtO Value ................................................................................................................. 15
7.2 AtS ............................................................................................................................ 15
7.3 AbS ........................................................................................................................... 15
7.4 tr................................................................................................................................1
5

7.5 SHt & Fuses: General Electrical Short Troubleshooting...................................... 15
7.6 SSH........................................................................................................................... 16
CONTROL VARIABLES......................................................................................................... 16
8.1 Introduction to Control Variables........................................................................... 16
8.2 SP.............................................................................................................................. 16
8.3 OS ............................................................................................................................. 17
ADJUSTMENT VARIABLES .................................................................................................. 17
9.1 C or F........................................................................................................................ 17
9.2 C-H, C-L, or PID Set-Point Methods ....................................................................... 17
9.3 Fan Temperature Diagnostic.................................................................................. 17
NO SET-POINT MODE (SP0)................................................................................................. 18
10.1 Test Fridge Voltage ............................................................................................... 18
10.3 Sensor Troubleshooting Test............................................................................... 18
10.4 MAX/MIN Fridge Voltage Record.......................................................................... 18
AUTO TUNE MODE................................................................................................................ 19
11.1 Auto Tune Procedure............................................................................................ 19
11.2 Auto Tune & Set-Point Function .......................................................................... 19
RV STORAGE & STARTUP TIPS .......................................................................................... 20
12.1 Storage – RV Batteries; LP Gas; Fridge .............................................................. 20
12.2 Get Ready to Go – Dry Run................................................................................... 20
12.3 RV Battery Voltage & Fridge................................................................................. 20
12.4 Get Fridge Ready for Travel.................................................................................. 21
RTD TROUBLESHOOTING.................................................................................................... 21
13.1 Check Boiler Sensor ............................................................................................. 21
13.2 SHt Error................................................................................................................. 21
RTD TABLES.......................................................................................................................... 21

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SAFETY
1.1 Acronyms and Abbreviations
ARP: ARP Control = Fridge Defend
RTD: ARP Control temperature sensor;
Resistance Temperature Detector is the type
of sensor used.
Q: Flow of fluid either as a gas or liquid.
SPAR: Single Pressure Absorption
Refrigerator.
1.2 Hazard Information
Hazard information includes terms, symbols
and instructions used in this manual or on
the equipment to alert operating and service
personnel to the recommended precautions
in the care, use and handling of the ARP
Control.
1.3 Terms & Warnings Symbols
1.4 Work Safely
There are many ways to install the ARP
Control. Make safety your first priority!
The installer’s knowledge, skill, and ability
are important for safely installing the system
and maintaining or troubleshooting it. If you
are unsure of your ability to use the ARP as
a diagnostic tool, have a qualified individual
do the work.
1.5 Operation Safety
The ARP Control and 'ARPrvSafe' infer that
the use and operation of this control can add
a level of safety to your absorption
refrigeration system in your RV. No other RV
absorption refrigerator control monitors the
boiler temperature, and turns off the heat
source to the refrigerator before damage can
be done to the internal fluids in the
refrigerator cooling unit. The ARP cannot
prevent RV refrigerator failure if the
manufacture built the cooling unit in a
manner that would result in premature failure.
In addition, if damage to the cooling unit has
occurred before the ARP was installed; the
ARP cannot remedy this damage
__________________________________________________________________________________________
SETUP MODE
2.1 Activate SetUp Mode
On/Off Display SetUp
To place the control into SetUp mode, begin by turning
off the ARP Control (Please see User Guide →Turn off
ARP Control). When the control is off, the SetUp mode is
activated by holding*the right SetUp button and then
momentarily*pressing the On/Off button. When AtO is
displayed, release the SetUp button.
*Please see User Guide section BUTTON FUNCTION
& Ancillary Graphical User Instructions section Turn
ON Control in SetUp Mode .

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2.2 Types of SetUp Mode Variables
There are 3 types of SetUp mode variables as follows:
1) Reading Variable: Example, AtO is a reading type variable because the user can only
read the value. Its value is dependent upon another setting.
2) Process Value*: Example, the ARP stores values such as AbS. AbS is calculated by
the ARP and stored for diagnostics. The user cannot change the value of AbS, the
value can only be reset to zero in order to clear the present value so that the ARP can
record new values in the future.
3) Setting*:Example, C-H is a setting that the operator can change/toggle to modify the
setting. C-H setting changes the ARP set-point function. The present choice for the
set-point will be displayed in the Reading Variable AtO.
* Please note that all Process Values and Setting changes need to be stored before
exiting the SetUp mode. See 2.22 Store Settings.
2.3 SetUp Mode Button Operation
The three buttons on the ARP Control that performs the following functions when in the SetUp
mode:
On/Off Button: Turn off the control by pressing and holding till OFF is displayed, and then
cleared.
Display Button: The display button is used to advance to the next SetUp variable. By
repeated pushing of the display button the variables will advance to the store function (S--),
then Er0, and then rotate back to the first variable AtO.
SetUp Button: The SetUp button will change the value of either a Process Value or a Setting
variable. Each push of the SetUp button will increment the value by 1 up to the maximum value,
and then rotate back to either zero or 1 to restart the sequence.
2.4 AtO Reading
AtO will display followed by the present value or Set-
Point function*selection, see 2.16 Set-Point Function
Setting. The following table shows the default values for
AtO:
Set-Point Function AtO Value
C-H C-H
C-L 196
PID 196
Example of default value being displayed:
*Use the charts for both AtO and AtS to determine the
present Set-Point function and values.

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2.5 AtS Reading
AtS complements the AtO reading by providing further
Set-Point function selection information as follows:
Set-Point Function AtS Value
C-H 217
C-L C-L
PID 231*
*If the Set-Point function has been set to PID, AtS will
display a value. The default value is 231, more on this
subject in the Auto Tune and OS sections.
2.6 AbS Process Value
On/Off Display SetUp
AbS is the maximum temperature the boiler has reached.
The example below, 200C (See 2.15 Temperature Units)
would be the maximum temperature recorded by the
ARP since the last time that AbS was cleared.
Please see section 7.3 for detailed information.
By pressing the SetUp button, the AbS value will be
cleared. When the AbS value has been cleared, -LO will
flash on the display until the control is put into the ARP
mode to record a new maximum value.
Any changes must be stored, see 2.22 Store Setting.
Please note that if AbS is greater than 250°C (482°F)
there may be a wiring or cooling unit issue, please
contact ARP technical support.
2.7 tr Process Value
Tr is the number of times that the ARP Control has
triggered since the value was last cleared. The following
example shows that the ARP turned off the fridge twice:
Please see section 7.4 for further info.
Push the SetUp button to zero the tr value. Also see 7.4.
Any changes must be stored, see 2.22 Store Setting.

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2.8 OPn Process Value The OPn value is a count of how many times the ARP
boiler sensor has had a wiring or sensor open condition.
Please see section 3.4 OPn for further information.
If there is an intermittent problem due to vibration or a
bad crimp connection, OPn will record the total number of
times the circuit opens and closes. Push the SetUp
button to zero the OPn value. Any changes must be
stored, see 2.22 Store Setting.
2.9 SHt Process Value
The SHt value is a count of how many times the ARP
boiler sensor has had a short circuit. When the ARP
Control is in the ARP mode of operation, and either the
wiring or sensor is measured as a short circuit, SHt will
flash on the screen. SHt will record the total number of
times the boiler sensor has an intermittent short circuit
and then returns to normal operation. A short in the
sensor circuit is usually do to either the two sensor wires
touching or a sensor wire shorted to chassis ground.
See 3.5 SHt and RTD TROUBLESHOOTING for further
information.
2.10 SSH Process Value
On/Off Display SetUp
The SSH value measures the boiler steady-state
maximum temperature. This value is only valid if the
control has been set to the PID control mode, see Set-
Point Function Setting section below.
If the control is tripping in the PID control mode, this
variable is very valuable for troubleshooting when
combined with the above AbS value. If the AbS value is
greater than the AtS value, the start up is tripping the
fridge. If the SSH value is greater than AtO value, the
control is tripping when in steady-state operation.
2.11 FAn Setting
FAn is the temperature setting at which the ARP will turn
On/Off the fan. There are six fan temperature settings to
select from.
For a non-fan type ARP Control, the fan setting is a fixed
number 0 and cannot be changed.
By momentarily pressing the SetUp button the fan control
temperature can be set to a desired value. Any changes
must be stored, see 2.22 Store Setting.
4 is the default fan setting value.

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Fan
Setting ON Temperature °F OFF Temperature °F
000 Fan Off
001 110 95
002 115 100
003 120 105
004 125 110
005 130 115
006 135 120
2.12 SP Setting
SP raises the set-point value of the ARP Control. The
default setting for SP is 5.
See section 8.2 for further information.
2.13 OS Setting
The OS setting is used for the restart of the refrigerator.
This value is rarely, if ever changed.
The default setting of OS is 5.
See section 8.3 for further information.
2.14 Adjustment of SP or OS Settings
By pressing the SetUp button the control enters into the
adjustment mode. Both SP and OS are adjusted in the
same manner as described below.

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When in adjustment mode, each subsequent press of the
SetUp button will increment the value by 1.
Store any setting change, 2.22 Store Setting
2.15 Temperature Units
The boiler temperature units can be changed from
degrees Celsius (C) to degrees Fahrenheit (F). Cis the
default value.
Press the SetUp button to change the setting. Following
is an example of the display for each setting:
Please see 9.1 for further info.
Store any setting change, 2.22 Store Setting.
2.16 Set-Point Function Setting
The ARP has three Set-Point control functions as follows:
1) C-H is the Set-Point control high mode. This is the
default mode and would be considered the plug-n-play
mode. This setting works on most refrigerators.
2) C-L is the Set-Point control low mode. This mode is for
fine tuning your control so that the maximum protection
for your fridge is achieved on smaller refrigerators.
Please see 2.4 AtO Reading and section 9.2
On/Off Display SetUp
3) The PID Set-Point control function is used on
particular refrigerators. A partial list of cooling units that
may need this control setting are some Dutch Aire
(Amish) cooling units, Norcold 1210 & 2118 cooling units
made after the year 2013, and some older Dometic
cooling units.
Please use the Contact Us form on www.ARPrv.com
website for any questions or concerns.

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2.17 Defrost Setting/IEC
Periodic Test
For refrigerators that have a
defrost cycle that is timed to turn
off the fridge for 2 hours, such as
the Norcold 1200, 2110, N3150, …. the PEr setting can
override the defrost cycle thereby providing improved
cooling in warm weather.
on is the default setting. Per = on means the IEC
periodic test of the ARP occurs every 24 hours. In
addition, the factory defrost cycle is defeated resulting is
a cooler fridge in hot weather. See our defrost fans for
fridge.
Use the right button to toggle to the oFF setting. When
PEr = oFF, the IEC periodic test of the ARP is not
preformed. Nor does the ARP defeat the defrost cycle,
thus the fridge runs with its factory defrost cycle.
2.18 Software Version Reading
The next setting is the software version of the control.
This software version example is 4.1 which is the ARP +
Fan Control version.
For the non fan-control version this value would be 4.0.If
you are using this manual your software version should
be either 5.0 or 5.1.
2.19 Serial Number Reading
The next two settings display the ARP control serial
number. Following is an example of what the display will
flash out for the serial number 65,535:
2.20 Audible Alarm (5.1 only)
On/Off Display SetUp
This setting controls the Audible Alarm or beeper.
on is the default setting. For some IEC tests the alarm
will sound while the display shows the error that resulted
in the alarm.
Use the SetUp button to toggle the alarm to oFF to
prevent the alarm from sounding. Save setting with S--.
2.21 Restore ARP Defaults

ARP Control v5.x Troubleshooting Guide 0©2013-2020 ARPC L.L.C. All rights reserved. 804/20/202
This setting restores the default settings that came with
the ARP when new. If Auto Tune is run by mistake, the
original settings can be restored by pressing the SetUp
button.
The display will flash:
and then return to the original screen. Proceed to the
next step to save your new settings.
2.22 Store Settings
The variable to save changes to SetUp is S--; any
settings that have been changed can be stored by
momentarily pressing the SetUp button as seen in the
next figure.
Release the SetUp button as soon as StO is displayed.
StO has to be displayed for the control to save the new
settings. If you do not want to save settings, proceed to
Exit SetUp Mode section.
2.23 Display Error Messages
The Er0 variable holds any IEC error messages stored
for the life of the control. Thus, always write down the
date any errors are viewed for future reference. It is not
unusual to see some errors recorded due to the nature of
RV electrical systems.
The SetUp button will toggle through all errors recorded.
will be display if no errors are
recorded.
If there are errors recoded, the first error message will
immediately appear, followed by the number of times this
particular error has been recorded. Use the SetUp button
to toggle through all of the error messages. Once the
error messages roll back to the first error recorded, use
the Display button to exit the Er0 and return to AtO.
2.24 Exit SetUp Mode

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If you do not want to save any
changes, just turnoff the control
by holding the On/Off button
without storing changes. This
feature is so that one can exit
SetUp without making any
changes if it is thought a mistake
was made.
Otherwise, after using the above Store Settings, hold
down the On/Off button until OFF advances across the
screen as seen in the figure to the left.
Remember to turn on the ARP Control in the ARP
mode after using the SetUp mode. .
ARP ERROR MESSAGES
IEC Type Accessory; Redundancy; Systematic Faults & Self-Checks
The ARP Control is a hybrid single channel IEC type accessory safety controller with a periodic
self-test structure. Software is designed using a single microcontroller unit (MCU) compliant to
ISO TS 16949:2009 to execute functions as required with optional periodic self-tests which will
occur every 24 hours when activated. The self-test checks most of the critical functions of the
electronic control. The reason that the ARP Control is referenced as a hybrid is that it is similar
to a dual MCU controller in that the ARP has an external watchdog timer (exWDT) that will turn
off the refrigerator and sound an alarm (v5.1) if the MCU becomes stuck and stops processing
code. The exWDT will try and restart the MCU, but if it is unsuccessful, depending on the
version of control, the operator is alerted to take appropriate action based on the operator’s
discretion. Because the ARP is an accessory safety controller, the ability to control the
refrigerator process is similar to a thermal fuse on the power supply to the fridge which limits
the controls ability for testing and self-checks.
Fridge OFF; Buzzer Sounding (v5.1); Right Dot Illuminated
If the Fridge Defend MCU has a critical error, and the
external watchdog timer (exWDT) asserts control, the
control will turn off power to the yellow wire which
controls the fridge. The right dot will be illuminated
without flashing. This is the only occurrence of the right
dot being illuminated without flashing. Check to see that
the control has 12VDC at the red wire. If so, disconnect
red wire; wait 30 seconds, reconnect. If the error does
not go away please contact support.
3.1 Error Message List
The following charts are divided up into the types of error messages:
•Operational Errors: These are errors that will display as the control is running or the
user is performing a test with one of the buttons.
•Startup or Periodic Test Errors (SPT): These are errors that will be tested at startup,
and thereafter every 24 hours when PEr = on, see section 2.17.
The Nature of Error column gives a brief description of the error. Go to the Section column to
find where to read more about the particular error. The Audible Alarm (V5.1 only) column
gives a definition of the alarm when it is turned on, see 2.20 for alarm setting.
Operational
Error Section Nature of Error Audible Alarm
(v5.1 only)
XYZ 3.2 Numbers on Display (not an error)
*Err 3.3 Control Variable Erasure
Opn 3.4 Boiler Sensor Error Short beep every second

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SHt 3.5 Boiler Sensor Error Short beep every second
-LO 3.6 Boiler Sensor Out Of Range
*O*F*8 3.7 ARP Has Attempted to Restart Fridge 5 Times and
Failed Fast and short beep
*H*O*8 3.8 Excess Temperature Shutdown (Boiler has reached
250C) Fast and short beep
OR (OA) 3.9 Fan Sensor Out Of Range (not an error)
bAd 3.10 Auto Tune Failure
F4 or F5 3.11 Contact ARP Control (only tested by operator with
SetUp button)
E 8 3.12 Contact ARP Control
E10 3.13 ARP Relay Error Short beep every second
E11 3.14 Contact ARP Control Continuous alarm
SPT Error
(IEC type test) Section Nature of Error Audible Alarm (v5.1 only)
F1 3.15 MCU ADC Error Checker
F2 3.16 ARP Relay Error Short beep every second
F3 3.17 Boiler Sensor ADC Cal Short beep every second
F6 3.18 MCU Set-Point Memory CRC Short beep every second
F7 3.18 MCU Set-Point Tune Memory CRC Short beep every second
E12 3.19 MCU Port Registry
E13 3.18 MCU Code Memory CRC
E14 3.19 MCU Program Counter
E15 3.19 MCU CPU Register
3.2 123 Numbers on Display (not an
error)
If the fridge is off, and the operator views
numbers on the display, this is not an error
message. The ARP has detected an
overheat situation and is in a countdown
period until the ARP restarts the fridge. The
countdown period is the time until the ARP
attempts a safe restart of the refrigerator. For
example, if 056 is displayed on the screen, it
is 56 minutes until the control will restart the
fridge, just keep the door of the fridge closed.
Do not turn off the ARP Control, please allow
the ARP to restart the fridge. By turning off
the ARP one prevents the ARP from doing its
job. If the ARP is turned off and then back on
the fridge will overheat again. See ARP User
Guide section ARP Protection Period
(What are the numbers on the display?) for
more information on the overheat event.
3.3 *Err (first dot on upper left)
In ARP Mode a single dot followed by Err
indicates that the ARP memory is cleared.
This can happen if the device has been Auto
Tuned incorrectly, or on rare occasions
surges/brown-outs less than minimum
voltage level of 10.5VDC or greater than
22VDC. Proceed to Restore ARP Defaults
section to reload default values.
3.4 OPn Boiler Sensor
This message will be flashed on the LED
display to warn the operator that there is an
error with the RTD and/or the RTD wiring.
The ARP is disabled because it cannot
function without the RTD. Thus, the cooling
unit is not protected by the ARP at this point;
the refrigerator operates just as it did when it
came from the manufacture. See 2.8 OPn
Process Value to clear the error after fixing
any issues or to use the recorded value for
diagnostics.
DANGER Operator must take action to
resolve the cause of the RTD error.
Possible causes of RTD error:
a) RTD has failed OPEN. Test RTD
resistance with Ohm meter that has less than
0.3mA current for the Ohm test function. Use

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the RTD Table at the end of this document
for reference.
b) RTD wires from control to the sensor are
broken or have a bad connection. A
resistance test from the control to the wire
connections at the RTD should show open or
high resistance in this case. If RTD wire has
become frayed or has an intermittent
connection, moving the wire while observing
the resistance of the wire under test should
show a change of resistivity. Replace any
wires that indicate high resistance.
3.5 SHt Boiler Sensor
If the RTD sensor is shorted, SHt will be
flashed out. See 2.9 SHt for further info.
User should disconnect the sensor and
check its resistance value by using the table
at the end of this document. If the resistance
substantially differs from the table, the
sensor has failed. Please contact ARP
Control for a new RTD. Also see RTD
TROUBLESHOOTING and perform these
tests.
3.6 -LO Boiler Sensor Reading
The ARP boiler temperature sensor is
measuring a value lower than 0°C (32°F).
3.7 *O*F*8
Depending on the conditions, it will take
about 4-5 hours, and many restart attempts,
before the ARP turns off the system and
warns the operator by displaying *O*F*8 on
the display. At this point the operator must
restart their system by turning off the ARP
after the boiler has cooled. As a rule of
thumb, using caution to avoid being burnt,
one should be able to touch the boiler
housing without burning your hand when the
boiler has cooled to a safe temperature.
DANGER Care must be exercised
during a restart in this situation. It may be
that the refrigeration unit needs maintenance
that is beyond the abilities of the operator. Or,
the cooling unit has failed, and by turning off
the Fridge Defend, the boiler will experience
unsafe runaway temperatures. If the ARP
keeps trigging due to high boiler
temperatures at each successive attempt to
restart the refrigerator, the ammonia in the
system may need to be remixed, or the
cooling unit may have completely failed.
Because one cannot easily remove the
refrigerator and tip it over to mix the fluids
such as described in the burping section 4.5,
the motion of driving may resolve this
situation. The motion of driving helps mix the
fluids and will help cool the boiler thereby mix
the ammonia back into the system fluids. It is
emphasized that you are in charge of
safety, please take your problems to a
qualified service facility if you do not feel
qualified to resolve any issues that may
affect safety.
3.8 *H*O*8
If HO8 is displayed with all of the dots
illuminated, the ARP has turned off the
refrigerator at a very high temperature. It is
important to check the fridge for failure
before attempting to resume operation. The
cooling unit must be allowed to cool to
ambient temperature if this event occurs.
Please seek a qualified RV technician if you
are not qualified to make safe decisions.
See 3.20 ARP Reset Procedure for
additional information.
3.9 OR (OA) Fan Temp Reading
When measuring the fan temperature in the
ARP mode with the center button, if OR (OA)
is displayed the fan sensor is outside of its
normal measurement range, which is from
35F to 155F.
3.10 bAd
If the ARP Control is in the Auto Tune mode,
and the boiler sensor exceeds 250C
(482F), the bAd error will flash. A possible
cause for this message is the ARP boiler
sensor is too close or touching one of the
heat sources, either the electric heaters or
the flue tube. Check the sensor and
reposition before running Auto Tune again.
3.11 F4 or F5 SetUp Button Test
When the control is in the ARP Control mode,
the SetUp button performs tests of the
controller. If during the automatic controller
test F4 or F5 is displayed, contact ARP

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Control by using our Contact Us form at
www.ARPrv.com
3.12 E8 Error
It would be rare if ever that E8 would appear.
If E8 does appear the first step is to turn off
the control and turn back on to see if the
error clears? If the error does not clear after
this procedure please contact ARP Control
by using our Contact Us form at
www.ARPrv.com.
3.13 E10 Flashing when Test ARP with
SetUp Button
If one is testing the ARP internal relay with
the SetUp button while in ARP control mode,
and E10 flashes, there is an internal relay
failure or the control has been installed
parallel with a recall device, see solution
below in the F2 at ARP Startup section.
3.14 E11 Trigger Event
The ARP Control detected an overheat
situation and the power was not turned off to
the fridge. See solution in F2 at ARP Startup
section, if solution cannot be found, contact
ARP and remove the ARP Control from
service.
3.15 F1 MCU ADC Error Checker
This error can occur due to electrical noise
on the RV wiring. This error will not affect the
ability for the control to measure boiler
temperature. Thus, it is not a critical error.
The best way to test if there is an issue, go to
the User Guide section 1.4, or below section
10.1 to read the fridge voltage with the ARP,
then check this voltage reading with an
accurate DMM. The readings should be
within +/-0.2 volts.
3.16 F2 at ARP Startup
F2 is tested at startup, and if the periodic
testes are enabled, this test checks that the
ARP internal relay can turn power off to the
yellow wire controlling the fridge.
If this error is seen after installation of the
ARP, the control has been wired incorrectly.
Solution: The control needs to be turned off
by disconnecting the ARP red wire. Next,
disconnect ARP yellow wire; be sure not to
ground this wire during testing. Reconnect
the ARP red wire so that control turns back
on. Check to see if F2 is still displayed? If F2
is not displayed, internal relay is functioning.
Solution, rewire ARP to be in series with
recall. If F2 is still displayed during startup
test while ARP yellow wire is disconnected,
contact ARP and discontinue use of control.
3.17 F3 Boiler Sensor ADC Cal
This error can occur due to electrical noise
on the RV wiring. This error can be checked
by service personnel by putting the control
into SP0 mode and perform a senor check,
section 10.3 below.
3.18 CRC Tests
These tests check the code within the MCU
for integrity.
F6 MCU Set-Point Memory CRC:
This test can fail for a number or reasons,
including but not limited to power supply
brown out (electrical noise on the RV wiring),
user operator error during Auto Tune, or
other events that result in a memory
corruption. This error can generally be fixed
by restoration of the factory default settings,
see section 2.21, Restore ARP Defaults.
F7 MCU Set-Point Tune Memory CRC:
Use the same set of rules stated above for
the F6 error. Also, this error is specific to an
improper Auto Tune session. If this is the
case, run Auto Tune again or see section
2.21, Restore ARP Defaults.
E13 MCU Code Memory CRC:
This error can occur due to electrical noise
on the RV wiring. The first step is to turn off
the control and restart it while viewing the
ARP display for error messages. If the
control passes all of the functional tests, then
this error may have been recorded due to
noise on the system during the automatic
test procedure. If this is the case, this error
will be cleared. Also, perform all of the
manual functional tests, see User Guide
section 1.7.
3.19 E12, E14, E15 MCU Tests
These errors can occur due to electrical
noise on the RV wiring. See E13 MCU Code
Memory CRC above for test procedure.

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3.20 ARP Reset Procedure
The ARP can be turned off, and the
refrigerator will resume operation as it did
from the factory. We do not recommend
turning off the ARP if it has detected an over
heat situation, please let the ARP do its job
and allow it to restart the fridge. By turning
the ARP off and then back on, the control will
be reset and resume monitoring boiler
temperature.
DANGER Please remember that when
the ARP is turned off, the refrigerator will
resume operation if the fridge main power
button is not turned off before the reset
procedure. If your fridge has overheated,
there is a problem that should be addressed
by qualified persons.
__________________________________________________________________________________________
INTRODUCTION to FRIDGE REPAIR
4.1 Refrigerant
The SPAR RV refrigerator, when constructed
properly is extremely reliable due to the fact
that the process is quite simple. The
refrigerant (working fluids) consists of water,
ammonia, and sodium chromate.
4.2 Boiler Operation
The heart of your RV refrigerator is at the
boiler. The boiler can also be called the
generator because the boiler ‘generates’ the
ammonia refrigerant. The boiler performs a
distillation process, the ARP monitors this
process and detects when ammonia is not
being generated. Think of the ARP as a heart
monitor keeping your fridge alive.
4.3 Boiler Pump
The heat source that drives your SPAR
simply separates the water and ammonia
(distillation). Ammonia boils at a lower
temperature than water, thus the heat source
boils the ammonia. Just like a coffee
percolator, the ammonia gas transports the
liquid water up a pump tube, at the top of the
pump tube the ammonia gas raises and the
water descends by the effect of gravity.
4.4 ARP Control and the Boiler
The ARP control is effective because of the
simple physics. If there is no ammonia in the
boiler assembly of your SPAR, the boiler
pump will not work. The result, the normal
temperatures required to drive the SPAR
system will rise. It takes heat energy to
change the ammonia from liquid to gas,
when this heat energy is not changing the
ammonia from liquid to gas; the heat energy
starts to destroy the SPAR. Restated, without
ammonia in the boiler, the heat energy will
cause the boiler temperature to rise until the
water in the SPAR starts to boil, this
damages your refrigerator. The ARP control
prevents the water from boiling in the SPAR
when installed and setup correctly.
4.5 Burping a SPAR
Folks that have been around RV and
stationary refrigerators such as a Servel
have heard of 'burping' the refrigerator.
Burping is necessitated by the fact that the
ammonia has not completed the SPAR
process and returned to the boiler. Burping
consists of turning the refrigerator over onto
its top. The burping procedure simply will
remix the ammonia and water in your SPAR.
As long as the system has not been
damaged by overheating and blockage of the
system, the refrigerator will resume operation
once the ammonia is returned to the boiler.
In most cases, burping is not necessary
when the ARP controls the boiler
temperature.
4.6 Abnormalities and Operator
Discretion
The ARP will turn off the heat source driving
your SPAR process before burping is
necessary. But it must be taken into account
that the ARP has sensed a rise in
temperature due to an abnormality in your

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SPAR. The ARP cannot determine the cause
of the abnormality. This is the responsibility
of the operator. Other than off-level operation
of the SPAR, and boiler over heating due to
wind currents that result in stagnation within
the cooling unit compartment, it is beyond
the scope of this document to cover all of the
causes for the SPAR boiler to overheat.
In the following sections of the
Troubleshooting Guide are suggestions to
help you resolve situations that may arise.
Again, it is the operator's responsibility to
insure that safe operation of the SPAR is in
effect. Although the ARP can give an
operator feedback, the operator must have
discretion to make decisions responsibly and
act on one's own. If there is doubt, please
take your RV to a qualified RV service center.
Following are ideas to consider that could get
you up and running, these suggestions are
circumstantial and are solely provided as
assistance to help you make good decisions
while on the road.
__________________________________________________________________________________________
HEAT SOURCES
5.1 Temperature & Pressure
The boiler temperature is an over all indicator
of your refrigerator health. It is advised to
check and adjust your LP gas pressure,
check your gas flame and adjust if necessary.
Only then record your 'normal' boiler
temperatures using both LP gas and the
electric heat source for future troubleshooting
reference. Please note, for the following
discussion, the LP gas temperature
measured by the ARP is generally about
10°C (18°F) higher than the temperature
measured by the 120VAC. A rule of thumb is
that the LP gas temperature will range from
170°C (338°F) to 190°C (374°F) depending
on the make and model of your SPAR. The
boiler temperature can vary with the RTD
location on the boiler tube also.
There are few causes of low boiler
temperature, low LP gas pressure, failed
electric heaters, and low cooling unit
pressure. Low cooling unit pressure is
covered in section 6.1.
5.2 Low LP Gas Pressure
Low LP gas pressure results in a cold gas
flame. The simple test for this problem is to
check the LP gas pressure with a manometer
and make sure there is 11 inches water
column pressure. See our LP Gas Safety
Video for filter cleaning.
5.3 Test Each Heat Source
An alternative to testing the gas pressure,
use the shore power (120VAC) heater to run
your refrigerator. If your ARP control
measures "normal" temperatures in the
range given above, but the LP gas does not,
one can deduce that there is an issue with
the LP gas portion of your refrigerator.
To test the electric heater, use the gas flame.
If the boiler temperature is at its normal value
using gas, but lower than normal using
120VAC, there may be a problem with your
120VAC operation
SPAR PRESSURE
6.1 Low Cooling Unit Pressure
The temperature at which a liquid changes
phase from liquid to gas (boils) is dependent
on two physical qualities: temperature and
pressure. The temperature measured at your
boiler is dependent upon your cooling unit
pressure. If the pressure inside your cooling
unit goes down, the temperature at which
your boiler will boil the refrigerant goes down
also. Previous to the ARP, the pressure
inside the cooling unit could only be
measured by a cooling unit rebuilder. Now,
the ARP can be used as an indicator by
which to measure the cooling unit pressure.
The first telltale sign of cooling unit failure is

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low temperatures measured at the boiler of
your cooling unit. If your heat sources are
confirmed to work fine, and you are
measuring low boiler temperatures, there
may be low cooling unit pressures indicating
failure of the cooling unit.
WARNING Please take your
refrigerator to be checked by a qualified
service technician to rule out any cause that
will result in abnormally low or high
temperature readings by the ARP.
__________________________________________________________________________________________
DIAGNOSTIC VARIABLE
7.1 AtO Value
The AtO value is preset to default values if
the control has not been Auto Tuned.
Otherwise, AtO is calculated during an Auto
Tune session, the base AtO value is not
adjustable other than by running Auto Tune
again. The value of AtO can be changed by
the C-H, C-L, and PID set-point function in
combination with the SP value.
7.2 AtS
AtS is only used for the PID set-point
function. AtS will not need to be changed
ordinarily. If fridge is in the PID mode, and
the ARP turns off the fridge consistently at
the startup, the AtS value can be raised
manually changing the OS setting. Also, the
AtS value is recalculated during an Auto
Tune session if the default setting is not
working. See ‘SSH’ value, AtS and SSH work
together for PID function.
7.3 AbS
The AbS value is the maximum temperature
measured at the boiler since the last time
that the value was zeroed. This variable is
very handy for testing and setting the
refrigeration control values. Auto Tune
always zeros this value.
Adjustment
The AbS value may be zeroed by pressing
SetUp button. Please store any new settings
as described in section 2.22.
Purpose:
This variable is handy for recording the
cooling unit boiler temperature while the
cooling unit is in a known phase of its
process. For example, one wants to know
the absolute maximum temperature of a
cooling unit after the ARP has shut down the
system due to an off-level overheat situation.
This will aid the operator in setting the value
of OS for a particular refrigerator installation.
Use the AbS variable in combination with the
No Set-Point mode when the ARP is not
equipped with data collection capability for
the recording of restart temperatures.
7.4 tr
The tr value is simply the number of times
that the ARP has triggered since the last time
the value was zeroed. When Auto Tune is
run, tr value is zeroed.
Purpose:
Knowing the number of times the control has
triggered helps the owner understand
situations where overheating of the cooling
unit boiler occurs. For example, climbing
steep grades in hot weather often will result
in an ARP trigger event. Another example,
RV rental firms can use this information for
damage deposit and other bookkeeping
purposes.
See section 2.7 for clearing this variable.
7.5 SHt & Fuses: General Electrical
Short Troubleshooting
Most RV techs are skilled at electrical short
diagnostics. This section is a brief set of
instructions on troubleshooting procedures if
repeated SHt errors are encountered.
If a short is occurring, the most likely cause
is a wire touching a ground somewhere. One
can disconnect the wire, thereby isolating the
ARP control from the short, and see if the
issue is still occurring? If the issue goes
away by disconnecting the wire, visually
inspect the wire for where the short circuit
may be? The most common cause of a short
is when wires rub on sharp metal and the