Dometic Qht User manual

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The Q3 and Qht Digital Controls
For Direct Expansion Systems
OPERATIONS MANUAL
Q3 Control Qht Control (with bezel)
Dometic Marine
Rev. 20170710
Part Number 0880107
L-2516 English

L-2516 ENGLISH
Table of Contents
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
READ THIS MANUAL BEFORE PROCEEDING . . . . . . . . . 1
CONTROLS OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . 1
FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
HOW ITWORKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
The Importance of Seawater Temperature . . . . 1
Power Interruptions . . . . . . . . . . . . . . . . . . . . . . 2
DESCRIPTION OF THE CONTROLS . . . . . . . . . . . . . . . . 3
IMPORTANT PROGRAMMING NOTES TOINSTALLER AND
END USER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
NORMAL HEATING OR COOLING CYCLE . . . . . . . . . . . . 5
REVERSING VALVE OPERATION . . . . . . . . . . . . . . . . . 5
INSTALLING THE DISPLAY PANEL . . . . . . . . . . . . . . . 5
MOUNTING THE DISPLAY . . . . . . . . . . . . . . . . . . . . . . 5
MOUNTING THE SENSORS . . . . . . . . . . . . . . . . . . . . . . 5
Ambient Temperature Sensor - required . . . . . 5
Seawater Temperature Sensor - optional . . . . . 5
Outside Air Temperature Sensor - optional . . . 6
Humidity Sensor - optional . . . . . . . . . . . . . . . . 6
OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
OPERATOR CONTROLS AND DISPLAY PANEL . . . . . . . . 6
Button Functions . . . . . . . . . . . . . . . . . . . . . . . . 6
MODES OF OPERATION . . . . . . . . . . . . . . . . . . . . . . . 6
Power On and Basic Modes . . . . . . . . . . . . . . . 6
Dehumidification Mode . . . . . . . . . . . . . . . . . . . 7
Adjusting the Set Point . . . . . . . . . . . . . . . . . . . 7
Fan Operation and Control . . . . . . . . . . . . . . . . 7
Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Display Inside Cabin Temperature . . . . . . . . . . 7
Dimming the Display . . . . . . . . . . . . . . . . . . . . . 7
Sleep Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Lockout Display Mode . . . . . . . . . . . . . . . . . . . 7
Anti-Ice Routine . . . . . . . . . . . . . . . . . . . . . . . . 8
PROGRAMMING THE CONTROL . . . . . . . . . . . . . . . . . 8
PROGRAMMING PROCEDURE . . . . . . . . . . . . . . . . . . . . 8
PROGRAMMABLE FUNCTIONS . . . . . . . . . . . . . . . . . . . 8
Customizing the Functions . . . . . . . . . . . . . . . . 8
Restoring Factory Default Settings . . . . . . . . . . 8
Description of Functions . . . . . . . . . . . . . . . . . . 8
Summary Table of Programmable Functions . 14
FAULT AND ERROR MESSAGES . . . . . . . . . . . . . . . . 15
HIGH-PRESSURE SHUTDOWN (HI / PS) . . . . . . . . . . . 15
In Cool Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 15
In Heat Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 15
LOW-PRESSURE SHUTDOWN (LO / PS) . . . . . . . . . . . 15
In Cool Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 15
In Heat Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 15
LOW-VOLTAGE SHUTDOWN (LO / AC) . . . . . . . . . . . . 15
SUMMARY OF FAULT CODES AND INDICATOR CODES . 16
INITIAL SYSTEM START UP . . . . . . . . . . . . . . . . . . . . 16
TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . 17
GENERAL SYSTEM TROUBLESHOOTING . . . . . . . . . . . 17
DIGITAL-CONTROLS TROUBLESHOOTING . . . . . . . . . . 20
MAINTENANCE OF SYSTEM COMPONENTS . . . . . . 21
CONDENSATE DRAINS . . . . . . . . . . . . . . . . . . . . . . . . 21
RETURN-AIR FILTER . . . . . . . . . . . . . . . . . . . . . . . . . 21
SEAWATER CONNECTIONS . . . . . . . . . . . . . . . . . . . . 21
SEAWATER PUMP . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
SEAWATER STRAINER . . . . . . . . . . . . . . . . . . . . . . . . 22
REFRIGERANT GAS . . . . . . . . . . . . . . . . . . . . . . . . . . 22
REVERSING VALVE . . . . . . . . . . . . . . . . . . . . . . . . . . 22
CONDENSER COIL . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
WINTERIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
OPERATIONAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
CABLE LENGTHS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
SYSTEM INPUTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
SAMPLE WIRING DIAGRAMS . . . . . . . . . . . . . . . . . . . 24

Q3 & Qht Controls for Direct Expansion Systems Read This Manual Before Proceeding
L-2516 ENGLISH 1
INTRODUCTION
The Q3 and Qht are microcontroller-based units designed for use with reverse-cycle direct expansion (DX) air conditioning
systems. This manual provides all necessary information for proper installation and operation of the Q3 and Qht controls. Poor
installation or misunderstood operating parameters will result in unsatisfactory performance and possible failure.
READ THIS MANUAL BEFORE PROCEEDING
This manual contains essential information concerning the operation of the control system. It is very important that you read and
understand the contents of this manual before using the equipment, and it should be kept on the boat for future reference.
Read this manual completely before you proceed with the installation and operation of the controls. If you have questions or
require assistance with your Q3 or Qht control, call your Dometic dealer or the Service Department at [phone].
The Q3 and Qht controls are covered under the existing Dometic Owner’s Limited Warranty Policy. Incorrect installation, neglect
and system abuse are not covered under the warranty policy.
CONTROLS OVERVIEW
There are two different controls that can operate a Q-Logic or U-Board system:
•Q3 - Rectangular in shape with a bezel look and LED indicators, this display was designed as an economical version of
the Qht. The Q3 control is only compatible with a Q-Logic or U-Board and is not backward compatible with an SMXII
system
•Qht - Using the newest high-technology (ht), this European-style control with LCD display fits into a decorative Vimar®
Idea bezel and has many new features. The Qht control is only compatible with a Q-Logic or U-Board and it is not
backward compatible with an SMXII system.To distinguish between Qht and SMXht, the Qht has a "Compatible With
Q-Logic Only" label displayed on the Qht mounting flange.
While the programming procedure of the Q3 and Qht controls is the same, there are differences in the look of the buttons and
and the way the information is presented in the displays. Differences are noted in this manual where applicable. Familiarize
yourself with the operation and programming sections of this manual.
FEATURES
HOW ITWORKS
The basic principle behind an air conditioner is the movement of heat. In a marine DX air conditioner, heat is removed from the
inside cabin air and transferred to the seawater. In reverse-cycle heating, the refrigerant flow is reversed and heat is extracted
from the seawater and discharged into the living space. The efficiency of the system operation depends on both seawater and
cabin temperatures.
THE IMPORTANCE OF SEAWATER TEMPERATURE
In Cool Mode, the air conditioner will operate most efficiently in seawater temperatures below 90°F (32°C). At higher seawater
temperatures the unit will operate, but at a reduced capacity. A high-pressure shutdown may occur at higher seawater
temperatures.
Standard Features Optional Features
• Universal 115/230 volt, 50/60 Hz AC power supply.
• User-friendly four- and five-button display panels.
• Option to display temperature in degrees Fahrenheit or
Celsius.
• 33 programmable functions.
• Nonvolatile memory requires no backup power.
• Switch inputs for High/Low Refrigerant pressure.
• Humidity Mode control.
• Anti-icing cycle prevents evaporator icing.
• Programmable fan operation.
• Programmable compressor delays.
• Programmable display brightness.
• Air Filter Cleaning or Replacement Timer.
• Low-Voltage Monitor.
• Outside temperature sensor.
• Seawater inlet temperature sensor.
• Auxiliary heating control capabilities.
• Humidity sensor for advanced humidity control.

How It Works Q3 & Qht Controls for Direct Expansion Systems Operations Manual
2L-2516 ENGLISH
In Heat Mode, the opposite is true. As the seawater gets colder, there is less heat available, and the heating efficiency is
reduced. Full heating capacity is obtained at approximately 55°F (13°C) seawater temperature. Performance drops to about
50% of rated capacity in 40°F (4.4°C) water. Below this, the system pressure can be so low that the unit will shut down on low-
pressure fault. This problem is compounded when the cabin is also cold. See “FAULT AND ERROR MESSAGES” on page 15.
POWER INTERRUPTIONS
The control board has built-in protection against sudden power interruptions. The system automatically stores the current
operating configuration in permanent memory every time any changes are made. When AC power is lost, the control board
retains these settings and resumes using them when AC power is restored.
WARNING
Do not operate your air conditioning unit in water that is colder than 38°F (3.3°C). Doing so could lead to water freezing
in the condenser coil which can cause damage to the unit.

Q3 & Qht Controls for Direct Expansion Systems Description of the Controls
L-2516 ENGLISH 3
DESCRIPTION OF THE CONTROLS
Figure 1: Q3 Diagram - Control Display Panel and Indicators
Table 1: Q3 Diagram Description of Control Display Panel and Indicators
1Data Display - Large LED readout displays current
temperature, set point, programmed values and error messages.
9AUTO Mode Indicator - Lights when Auto Mode is selected.
Flashes if optional Aux Heater is enabled (see Programmable
Function “23: Aux Heat Enabled/Disabled” on page 12).
2AUTO Fan Mode Indicator - Lights when fan is running in
Automatic Fan Mode.
10 HEAT/AUX HEAT Mode Indicator - Lights when Heat Mode
is selected or indicates compressor is on when heating in
AUTO mode. Flashes when you press the MODE button a
second time in Heat Mode to select the optional Aux Heat
Mode (refer to Aux Heat Operation).
3Fan Speed Indicators - Column of three LEDs that indicate
the current fan speed of high, medium, or low (refer to fan speed
operation).
11 COOL Mode Indicator - Lights when Cool Mode is selected
or indicates compressor is on when cooling in AUTO mode.
4FAN Button - Press to select Automatic or Manual Fan Mode,
indicated by the AUTO Fan LED indicator being on or off. In
Manual Fan Mode, additional presses of the Fan button will
adjust fan speed higher, then lower, then back to AUTO. In
AUTO Fan, fan speed is controlled by the control board as a
function of the difference between set point and inside
temperature. See Programmable Function “4: Fan Response
Differential” on page 9.
12 OFF Mode Indicator - Lights when system is off. Note that
the Data Display remains on. You can continue to adjust set
point, display temperature readings and activate the manual
fan to circulate air while the system is in the Off Mode.
5UP Button - Press to adjust set point up. In programming mode
press to scroll through program modes and adjust values.
13 Cooling Indicator - A dot in the upper left corner of the data
display lights to indicate the compressor is running in COOL
mode. In AUTO mode, the COOL LED indicator lights to
indicate the compressor is running.
6DOWN Button - Press to adjust set point down. In
programming mode press to scroll through program modes and
adjust values.
14 Heating Indicator - A dot in the upper left corner of the data
display lights to indicate the compressor is running in HEAT
mode. In AUTO mode, the HEAT LED indicator lights to
indicate the compressor is running.
7MODE Button - Press to cycle through the modes of operation
(refer to indicators). Mode sequence selections are OFF, COOL,
HEAT, AUX HEAT (optional), AUTO, and DEHUMIDIFY.
15 Set Point Indicator - A dot in the upper center of the display
lights to indicate the set point is being adjusted. Normally
display defaults to inside temperature.
8DEHUMIDIFY Mode Indicator - Lights when the Dehumidify
Mode is selected. Flashes if optional humidity sensor is
connected and operating in Cooling Mode.
16 Manual Fan Mode Indicator - AUTO Fan indicator turns off
when fan is running in Manual Fan Mode.
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Description of the Controls Q3 and Qht Controls for Direct Expansion Systems
4L-2516 ENGLISH
Figure 2: Qht Diagram - Control Display Panel and Indicators
Table 2: Qht Diagram Description of Control Display Panel and Indicators
1Data Display - Large LCD readout displays current temperature,
set point, programmed values and error messages.
9Fan Speed Indicator - A row of five bars indicate the current fan
speed, with more bars indicating a higher fan speed and fewer bars
indicating a lower fan speed.
2Set Point Indicator - Display shows SET when set point is being
adjusted. Normally display defaults to inside temperature.
10 Fan Mode Indicator - The word MANUAL displays when the fan is
running in Manual Fan Mode. The word MANUAL does not display
when the fan is running in Automatic Fan Mode.
3Aux Heating Indicator and Aux Heat Mode Indicator (optional) -
A solid dot displays next to the words AUX HEAT when the electric
heater is on and running in Aux Heat mode. The words AUX HEAT
display when you are in Aux Heat mode. (Press the MODE button
to select the optional Aux Heat Mode.) See Programmable Function
“23: Aux Heat Enabled/Disabled” on page 12.
11 Dehumidify Mode Indicator - The word DEHUMIDIFY displays
when you are in Dehumidification Mode. It flashes if optional
humidity sensor is connected and operating in the Cooling Mode.
(Press the MODE button to select Dehumidification Mode.)
4Heating Indicator - A solid dot displays next to the word HEAT
when the compressor is on and running in Heat mode.
12 FAN Button - Press to select Manual or Automatic Fan Mode,
indicated by the word MANUAL displaying or not displaying. In
Manual Fan Mode, additional presses of the FAN button will adjust
fan speed higher, then lower, then back to Automatic. In Automatic
Fan Mode, fan speed is controlled by the control board as a
function of the difference between set point and inside
temperature. See Programmable Function “4: Fan Response
Differential” on page 9.
5Cooling Indicator - A solid dot displays next to the word COOL
when the compressor is on and running in Cool mode.
13 UP Button - Press to adjust set point up. In programming mode
press to scroll through program modes and adjust values.
6Cool Mode Indicator - The word COOL displays when you are in
Cool mode. (Press the MODE button to select Cool Mode.)
14 DOWN Button - Press to adjust set point down. In programming
mode press to scroll through program modes and adjust values.
7Heat Mode Indicator - The word HEAT displays when you are in
Heat mode. (Press the MODE button to select Heat Mode.)
15 MODE Button - Press to cycle through the modes of operation
(refer to indicators). Mode sequence selections are COOL, HEAT,
AUTO, AUX HEAT (optional), and DEHUMIDIFY.
8AUTO Mode Indicator - A bracket and the word AUTO display to
the right of the words COOL and HEAT when you are in Auto Mode.
If optional Aux Heat is enabled (see Programmable Function “23:
Aux Heat Enabled/Disabled” on page 12), a bracket and the word
AUTO display to the right of the words COOL and AUX HEAT.
(Press the MODE button to select Auto Mode.)
16 POWER Button - Press to turn the system on and off. Note that
the Data Display remains on in the Off mode. You can continue to
adjust set point, display temperature readings and activate the
manual fan to circulate air while the system is in the Off Mode.
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Q3 & Qht Controls for Direct Expansion Systems Important Programming Notes To Installer and End User
L-2516 ENGLISH 5
IMPORTANT PROGRAMMING NOTES TOINSTALLER AND END USER
If your air conditioning unit is Cool Only (does not have a reversing valve), then you MUST set Programmable Function 19 to
“CL” for Cool Only. Once this parameter is set, the only allowable operational modes that can be selected are OFF, COOL, and
DEHUMIDIFICATION. (See Programmable Function “19: Cool-Only Mode” on page 12 for more information.)
NORMAL HEATING OR COOLING CYCLE
In Automatic Mode, heating and cooling are supplied as required. If Cooling is required, the system will start a cooling cycle
when the cabin temperature exceeds the set point by the Compressor Differential setting in Programmable Function 3 (1.5°F/
0.8°C by default) and will continue to cool until the temperature equals the set point. Similarly, if Heating is required, the system
will start a heating cycle when the cabin temperature is below the set point by the Compressor Differential setting and will
continue to heat until the temperature equals the set point.
If you select Cool Mode, only cooling is supplied. If you select Heat or (optional) Aux Heat Mode, only heating is supplied. The
cabin temperature in either mode is maintained within the Compressor Differential setting.
During a Cooling or Heating cycle, the fan will operate at a fan speed depending on the fan’s operational mode. If a Manual fan
speed is selected, the fan will operate at this speed at all times, even if the set point has been satisfied and the cooling or
heating cycle has ended. If the fan is in Auto mode, the fan speed will be determined by Programmable Function 4, the Fan
Response Differential, and Programmable Function 22, Fan-Speed Divisions. Please refer to these parameters for further
details on the fan speeds during Auto fan operation. When in Auto fan mode, the fan speed will return to low speed once the set
point temperature has been satisfied and the cooling or heating cycle has ended.
REVERSING VALVE OPERATION
The position of the reversing valve determines if the system is in Cool Mode or Heat Mode. When the reversing valve is not
energized, the system will operate in Cool Mode. When energized, the system will operate in reverse-cycle heating. In addition,
the reversing valve will toggle (switch back and forth) to relieve the system’s internal refrigerant pressures in these situations:
• Just before the system starts the compressor if the compressor has not run for less than 2 minutes.
• When a cycle is interrupted from the display panel by pressing the POWER button or changing the set point.
INSTALLING THE DISPLAY PANEL
MOUNTING THE DISPLAY
1. For the Qht display, make a rectangular cut-out in the panel where it will be mounted. The Qht cut-out size is 3-7/16”
(88mm) wide by 2-1/8” (54mm) high. For the Q3 display, only a 1” (26mm) round hole is required in the panel for
mounting.
2. Use the installation instructions included with your display to complete the mounting, securing the display with the
appropriate size and number of screws.
3. Plug one end of the display cable (6-pin connector) to the back of the display and the other end to socket labeled
“Display” located on the edge of the circuit board.
MOUNTING THE SENSORS
AMBIENT TEMPERATURE SENSOR - REQUIRED
Install the ambient temperature sensor in a proper location to accurately sense the room air temperature. Ideally, the sensor
should be located in a reliable return-air stream moving from the room to be controlled to the air conditioner it is plugged into.
Locating the sensor on the back of the air conditioner coil is not ideal and can result in false readings for several reasons. It is
best to locate the sensor just inside of a return-air grille or passage. The standard cable length for the remote air sensor is 7 feet
(2.1m). Plug in the sensor’s 6-pin connector to the “Inside Temp” socket located on the edge of the circuit board.
SEAWATER TEMPERATURE SENSOR - OPTIONAL
Install the optional seawater temperature sensor to monitor the temperature of the seawater feeding the air conditioner. Ensure
that the sensor is in direct contact with the copper pipe and use thermal mastic to ensure good heat transfer. Strap the sensor
wire in place for strain relief and to prevent the sensor from being accidentally removed. Plug the sensor’s 2-pin connector into
the “Loop Water Out” (blue) socket located in the corner of the circuit board.
NOTE
Do not staple any sensor cables when mounting.

Operator Controls and Display Panel Q3 and Qht Controls for Direct Expansion Systems
6L-2516 ENGLISH
OUTSIDE AIR TEMPERATURE SENSOR - OPTIONAL
Install the optional outside air temperature sensor to monitor temperature outside the cabin. Outside air sensor cables are
available in various lengths. Mount the sensor outside but not in direct sunlight. Plug in the sensor’s 6-pin connector to the
socket labeled “Outside Temp” (white) located on the edge of the circuit board.
HUMIDITY SENSOR - OPTIONAL
Install the optional humidity/temperature combo sensor to monitor the relative humidity of the cabin. Locate the sensor in the
same location as the ambient air temperature sensor. Plug in the combo sensor’s 6-pin connector to the “Inside Temp” socket
located on the edge of the circuit board. The control board automatically detects the presence of this combo sensor and
immediately starts measuring humidity.
OPERATION
OPERATOR CONTROLS AND DISPLAY PANEL
For the button locations and display functions, refer to Figure 1, Table 1 on page 3 for the Q3 control and to Figure 2, Table 2 on
page 4 for the Qht control.
BUTTON FUNCTIONS
•POWER button (Qht only) - Press and release to toggle between the On and Off Modes.
•MODE button - Press and release to toggle between the Off (Q3 only) and all other modes of operation.
•UP button - Press and release to display the set point. Press and hold the UP button to increase the set point. Set
point increases one degree each time the button is pressed.
•DOWN button - Press and release to display the set point. Press and hold the DOWN button to decrease the set
point. Set point decreases one degree each time the button is pressed.
•FAN button - Press to select the Automatic Fan Mode, the Manual Fan Mode, or to advance through the manual fan
speeds.
•Display Seawater Temperature (optional) - Press the FAN and UP buttons simultaneously to display the seawater
temperature (optional). If the seawater temperature is not available, open or shorted (closed), the display flashes “- -”
instead of a temperature reading.
•Q3 - The display flashes “SE” for one second then the seawater temperature displays in two segments: The
display flashes the first digit of the seawater temperature for one second, then the next two digits of the seawater
temperature for one second. The cycle repeats until the buttons are released.
•Qht - The word WATER displays, “SE” flashes for one second, then the seawater temperature displays in two
segments: The display flashes the first digit of the seawater temperature for one second, then the next two digits
of the seawater temperature for one second. The cycle repeats until the buttons are released.
•Display Outside Temperature (optional) - Press the FAN and DOWN buttons simultaneously to display the outside
temperature (optional). If outside temperature is not available, open or shorted (closed), the display flashes “- -”
instead of a temperature reading.
•Q3 - The display flashes “OU” for one second then the outside temperature displays in two segments: The display
flashes the first digit of outside temperature for one second, then the next two digits of outside temperature for one
second. The cycle repeats until the buttons are released.
•Qht - The word OUTSIDE displays, “OU” flashes for one second, then the outside temperature displays in two
segments: The display flashes the first digit of outside temperature for one second, then the next two digits of
outside temperature for one second. The cycle repeats until the buttons are released.
•Display Relative Humidity (optional) - Press the MODE and UP and DOWN buttons simultaneously to display the
relative humidity (optional). “HS” displays for one second then the two digits of relative humidity display for one second.
The cycle repeats until the buttons are released. If HS is not available, open or shorted (closed), the display flashes
“- -” instead of the humidity reading.
MODES OF OPERATION
POWER ONAND BASIC MODES
Press the MODE (Q3) or POWER (Qht) button to turn the system on. In three seconds, the system will start operating in
whichever mode it was running prior to the last shut down. For the initial startup, the control will be in Cool Mode.To change
mode before the system starts, press the MODE button before the three-second startup completes (while the display is
flashing). Or, while the system is on, press the MODE button at any time to change the mode.

Q3 & Qht Controls for Direct Expansion Systems Modes of Operation
L-2516 ENGLISH 7
The modes available are: Off, Cool, Heat, Auto (automatically switches between Cool and Heat Modes, depending on set point
requirement), Aux Heat (optional) and Dehumidification Mode.
DEHUMIDIFICATION MODE
Press the MODE button until the DEHUMIDIFY LED indicator lights (Q3) or the word DEHUMIDIFY appears in the display
(Qht). The display flashes “HU” during this mode of operation. When Dehumidification Mode is activated, the Humidity Control
Program automatically turns the air conditioning system on at timed intervals to remove moisture from the air. The system is
programmed at the factory for average values. To change the factory settings, see Programmable Function “10:
Dehumidification Pre-Circulation Time” on page 10, Programmable Function “11: Dehumidification Time” on page 10, and
Programmable Function “12: Dehumidification Overall Time Period” on page 10.
ADJUSTING THE SET POINT
To view the set point, momentarily press and release the UP or DOWN button. To adjust the set point, press the UP or DOWN
buttons to set the desired room temperature (press and hold either button to scroll). The set point range is 55-99°F (12.8-
37.2°C). After selecting the desired set point temperature, if no buttons are pressed for three seconds the display automatically
reverts to showing the inside cabin temperature. Inside cabin temperature is continuously displayed.
•Q3 - The upper center dot in the display lights when set point is being adjusted.
•Qht - The word SET appears in the display while set point is being adjusted.
FAN OPERATION AND CONTROL
Press the FAN button to adjust the fan speed while in Manual Fan Speed Mode or to switch between Manual and Automatic Fan
Speed Modes. The fan may be run manually whether the system is on or off. Automatic Fan Speed Mode can only operate
when the system is on. Fan behavior also depends on how the Fan Mode function is programmed: “C” for continuous or “I” for
intermittent running with the compressor. See Programmable Function “7: Fan Mode” on page 9.
•Q3 - When in Manual Fan mode, the AUTO Fan LED is off.
•Qht - The word MANUAL appears in the display when in Manual Fan mode.
MEMORY
The control has nonvolatile memory requiring no batteries or backup power. When power is lost, the operating parameters are
retained indefinitely. When power is restored, the control resumes operating as last programmed.
DISPLAY INSIDE CABIN TEMPERATURE
The control continuously displays inside cabin temperature. If Mode or Set Point is changed, after three seconds the display
automatically reverts to showing inside temperature. If inside temperature is greater than 99°F (37°C) or less then 0°F (-17°C),
the display shows either 99°F (37°C) or 0°F (-17°C) respectively as the maximum or minimum inside temperature.
DIMMING THE DISPLAY
Press the MODE and UP buttons simultaneously and repeatedly to select the brightness setting for the display.
SLEEP MODE
Sleep Mode dims all LEDs (Q3) or turns off the backlight (Qht). When in Sleep Mode, press any button to brighten the display,
and then operate as usual. See Programmable Function “18: Sleep Mode” on page 11.
LOCKOUT DISPLAY MODE
Press the MODE and UP and FAN buttons simultaneously to select the Lockout Display Mode setting. This mode locks the
display in the current mode selected. If a button is pressed, the display flashes “LC” for 2 seconds then goes back to displaying
the inside temperature. In Lockout Mode, the display shows inside temperature and the indicators operate as normal, but all
button presses are ignored until MODE and UP and FAN buttons are pressed simultaneously, then “UL” displays momentarily
and the buttons are unlocked for normal operation. In Lockout Mode all sensors operate as normal and any fault and error
codes will be displayed.
NOTE
When the system is in Dehumidification Mode, all system safeguard controls remain active. For example, if the line
voltage falls below preset limits, the system will automatically shut down. Or, if AC power is interrupted, the system
will automatically resume operation in Dehumidification Mode when power is restored.

Programming procedure Q3 and Qht Controls for Direct Expansion Systems
8L-2516 ENGLISH
ANTI-ICE ROUTINE
The control occasionally shuts down the compressor when in Cool Mode to allow any ice to melt that may have formed on the
evaporator coil. The Anti-Ice Routine shutdown occurs when the inside cabin temperature falls below 70°F (21°C). The default
setting of 70°F (21°C) can be adjusted. See Programmable Function “21: Anti-Icing Routine Adjustment” on page 12.
During a ten-minute cycle period, the compressor shuts off for 15 seconds for each degree below 70°F (21°C) (default). For
example, if the inside temperature is 67°F (19°C), the compressor will shut off for 45 seconds, and then run for nine minutes and
15 seconds, repeating this cycle in ten-minute intervals.
PROGRAMMING THE CONTROL
PROGRAMMING PROCEDURE
The Q3 and Qht must be in Off Mode prior to entering Programming Mode.
•Q3 - Press the MODE button and select the Off Mode.
•Qht - Press the POWER button to turn the control off or on.
Once in the Off Mode, then:
1. Simultaneously press and hold the MODE and DOWN buttons for three seconds.
•Q3 - “PO” flashes in the display while the buttons are being held. When “PO stops flashing and the OFF LED
flashes, you have successfully entered Program Mode.
•Qht - “PROG” flashes in the display while the buttons are being held. When “PROG” stops flashing and a flashing
“01” appears in the display, you have successfully entered Program Mode.
2. Press the UP or DOWN buttons to scroll until the desired Programmable Function Number (1-29) is displayed. See
Table 4 on page 14.
3. Press the MODE button to access the programmable value of the displayed Function Number. That function’s current
value and a flashing OFF LED (Q3) or the word “PROG” (Qht) will also be displayed.
4. Press the UP or DOWN buttons to change the value of that function.
5. Press the FAN button to save the new setting and return to Program Mode. Scroll to another function number and
continue programming, or press FAN again to exit Programming Mode and return to Off Mode.
PROGRAMMABLE FUNCTIONS
CUSTOMIZING THE FUNCTIONS
The system’s default settings may be changed by the installing dealer or end user.
A summary of the function settings, permitted values, and original factory default settings of each are listed in Table 4:
Programmable Functions - Ranges and Factory Defaults, page 14. Record the data for any function settings you change in the
Custom Settings column of that table.
RESTORING FACTORY DEFAULT SETTINGS
You can restore the original factory default settings and overwrite all the customized changes you made. To restore the factory
default settings, switch to Off Mode and then press and hold the UP and DOWN buttons simultaneously. Hold the buttons for
three seconds while “00” flashes in the display. Successful memory reset is indicated by a “1” flashing back and forth across the
display. Release the buttons. System returns to the Off Mode.
DESCRIPTION OF FUNCTIONS
1: Compressor Time Delay
(Factory Default: 0 seconds)
The compressor time delay is for staged installations where more than one system operates from the same power source.
Setting different staging delays for each compressor allows them to start at different times when turning on power to the system
or when power is interrupted. Stage the units at least five seconds apart. Minimum delay is 0 seconds and maximum is 70
seconds. At initial power up, the display will show the countdown for the compressor time delay setting.
NOTE
Whether your control is set to display temperatures in °F or °C, all temperature-related programming values must be
adjusted in °F only.

Q3 & Qht Controls for Direct Expansion Systems Programmable Functions
L-2516 ENGLISH 9
2: Fahrenheit, Celsius, or Auto Selection
(Factory Default: Fahrenheit)
Select F for Fahrenheit. Select C for Celsius. Select Auto to have the system automatically set the unit based on system voltage
frequency: For 60 Hz systems, F will be selected as the degree unit; for 50 Hz systems, C will be selected as the degree unit.
3: Compressor Restart Differential
(Factory Default: 12 = 1.5°F / 0.8°C)
The Compressor Restart Differential is the ambient temperature change needed for the compressor to cycle on and off. The
factory setting of 1.5°F should be adequate for most applications. Differential selections are available in increments of 1/8°F.
Thus, to change the setting one degree, you should add or subtract 8 (for 8-eighths). All program functions must be adjusted in
°F even if the temperature display is changed from Fahrenheit to Celsius (see Programmable Function 2). Be careful not to set
the Compressor Restart Differential too low, since this will cause the compressor to start and stop very often and place an
undue load on your electrical system and may shorten the life of the compressor.
4: Fan Response Differential
(Factory Default: 8= 1.0°F / 0.6°C)
When the fan is in the Automatic Fan Mode, its speed is governed by how much the room temperature differs from the set point.
The fan runs faster when the difference is greater. As the room cools or warms, and the temperature approaches set point, the
fan slows down automatically. The Fan Response Differential can be adjusted from 1/4°F to 4°F, in 1/8° increments. All program
functions must be adjusted in °F even if the temperature display is changed from Fahrenheit to Celsius (see Programmable
Function 2).
The fan speed range is divided by the control system into five equal increments. If the Fan Response Differential is set at 1/2°,
then the fan speed will change 20% for each 1/2° of temperature deviation from set point. Lowering the fan speed differential will
cause the fan to change speed more frequently as temperature changes. Raising the fan speed differential will result in slower
fan speed changes for a given temperature change. The factory setting of 1/2° is good for most applications, but you may wish
to try a slightly higher setting in your salon and a lower setting in your stateroom.
5: Low Fan Speed
(Factory Default: 38)
You can adjust the lowest fan speed to suit individual preferences. For instance, you may wish to decrease the low fan speed
setting in your stateroom to minimize fan noise.
6: High Fan Speed
(Factory Default: 85)
A blower will often reach its highest speed at a voltage lower than full line voltage. For example, at a line voltage of 120V, the
blower might reach its fastest speed at 110V. At higher voltages, the bower speed will not increase significantly.
The High Fan Speed Adjustment allows you to set the maximum high-speed voltage to the threshold of the blower high-speed
response. The control system divides the fan speed voltage steps into five equal increments (between the low-speed and high-
speed adjustments). Accurately setting the High and Low Fan Speed Adjustments can help ensure that each fan speed
increment step results in a noticeable change of fan speed.
• While in Program Mode, listen to the fan noise level and use the UP button to raise the displayed value past the point
that you can hear an increase in the fan noise level.
• Press the DOWN button to lower the voltage until you hear a drop in fan speed, then raise that number by 2 or 3 to
ensure that it is set at the highest speed.
7: Fan Mode
(Factory Default: Continuous)
You can select continuous or intermittent fan operation.
NOTE
If the Compressor Restart and the Fan Response Differentials are both set to the factory default or a comparable range
and the Automatic Fan Mode is on, then the fan will not run at high speed unless the cabin temperature rises 3°F
above set point.
NOTE
For most efficient operation of your system, you should normally keep the low fan speed at the highest possible
setting, consistent with a comfortable noise level. Running the fan speed too low may have an adverse effect on the
system and may cause the evaporator coil to freeze.

Programmable Functions Q3 and Qht Controls for Direct Expansion Systems
10 L-2516 ENGLISH
Select C and the fan will run continuously while the system is on. Select I for intermittent operation and the fan will cycle on and
off with the compressor.
8: AC Line Voltage Calibration
The control board assembly has a built-in voltmeter that senses AC line voltage and this feature displays the voltage being read.
The control board automatically responds to sustained low-voltage or high-voltage conditions by shutting down the air
conditioning system to prevent compressor damage. At installation, the control board voltmeter should be calibrated to line
voltage within +/- 1%. To check or re-calibrate AC line voltage:
• Line voltage will be displayed as the last two digits of the voltage. On 115V systems, 95V appears as “95”, 100V as
“00”, and 120V as “20”. On 230V systems, 190V will appear as “90”, 200V as “00”, and 230V as “30”.
• To check accuracy or to calibrate, turn off all on-board AC loads and measure the line voltage with an accurate
voltmeter.
• Press the UP or DOWN buttons to recalibrate the value as required.
9: Temperature Calibration
This feature calibrates the ambient sensor within a range of ±1%. The temperature sensor should be within one or two degrees
of actual room temperature. Note that setting increments are in °F even when the control is set to display °C. Adjust this
parameter to display the correct room-temperature reading.
• The sensed temperature is displayed. Place an accurate thermometer beside the sensor and compare the
temperatures.
• Press the UP or DOWN buttons to recalibrate the value as required.
10: Dehumidification Pre-Circulation Time
(Factory Default: 10 minutes)
The Humidity Control Program (HU) automatically operates the air conditioning system for a programmed time period to help
control humidity in the boat. This dehumidification feature works in three stages:
1. The fan comes on at high speed to circulate air for ten minutes.
2. The fan then drops to low speed, and the compressor cycles on in the Cool Mode to dehumidify.
3. After the dehumidification cycle, the system turns off. The process repeats according to the programmed time period.
The Compressor Time Delay (Programmable Function 1) setting governs when the dehumidification cycle starts. Every one-
second of compressor delay equals a six-minute advance into the dehumidification cycle.
The factory default settings are:
10: Pre-circulation cycle - 10 minutes
11: Dehumidification cycle - 30 minutes
12: Overall time period - 12 hours
The factory settings are adequate for most moderate climates and boats. For very humid climates, shorten the overall time
period and extend the dehumidification time. In dry climates, select a longer overall time period between cycles and a shorter
dehumidification time. Programmable Function 10 governs the pre-circulation cycle time and should not be changed.
11: Dehumidification Time
(Factory Default: 30 minutes)
The dehumidification time determines how long the compressor runs in the Dehumidification Mode (see Programmable
Function 10). The display shows the dehumidification time period in minutes.You can select 10, 20, 30, 40, 50 or 60 minutes.
Select a longer dehumidification time in climates with high humidity and a lower dehumidification time in climates with low
humidity.
12: Dehumidification Overall Time Period
(Factory Default: 12 hours)
This setting determines how often the system performs the dehumidification process. The display shows the overall time period
in hours. You can select intervals of 2, 4, 6, 8, 10, 12, 14 or 16 hours. Choose a shorter overall time period in climates with high
humidity and a longer overall time period in climates with low humidity.
NOTE
If you select intermittent fan operation, you should relocate the thermistor from the return air grill to a cabin wall where
it can best sense the average room temperature. Check with your dealer or call the Dometic Applications Department
for more information.

Q3 & Qht Controls for Direct Expansion Systems Programmable Functions
L-2516 ENGLISH 11
13: Software Revision Level
This setting displays the software version and revision level of the system. It will display a 2-digit number such as “05” for
version 5. Have this information ready prior to calling a dealer or the factory for service assistance.
14: Determining Your Product Type
This setting displays the product type of the system being used. Have this information ready prior to calling a dealer or the
factory for service assistance. “dE” displays for marine Direct Expansion Self-Contained and Remote Products; “CH” displays
for Chilled Water or Modulating Air Handlers.
15: Low-Pressure Switch Test
The Low-Pressure Switch Test is used to test the low-pressure circuit for a fault or to test for low charge in system. This test can
also be used to charge a system. Press the MODE button to enter the Low-Pressure Switch Test. During the test, the unit will
operate in Cool Mode at high fan speed, and the display will show “OA” (closed circuit) if the low-pressure switch circuit is OK or
“FA” (open circuit) if the low-pressure switch circuit has a fault or system is low on charge. Press the FAN button to exit this test
mode.
.
16: High-Pressure Switch Test
The High-Pressure Switch Test is used to test the high-pressure circuit for a fault or to test for an overcharged system or loss of
water flow. Press the MODE button to enter the High-Pressure Switch Test. During the test, the unit will operate in Cool Mode at
high fan speed, and the display will show “OA” (closed circuit) if the high-pressure switch circuit is OK or “FA” (open circuit) if the
high-pressure switch circuit has a fault or system is overcharged or has loss of water flow. Press the FAN button to exit this test.
.
17: LED/LCD SegmentTest
Press the MODE button to test the display. All LED segments (Q3) or LCD graphics (Qht) should display. Press the FAN button
to exit this test.
18: Sleep Mode
(Factory Default: On)
You can set the Q3’s LED brightness level to dim or you can set the Qht’s backlight to be on or off. Select “SL” for Sleep Mode
and the LEDs will remain dim or the backlight will remain off until a key is pressed, which will temporarily brighten the display.
Select “On” and the Q3’s LEDs will stay at the current brightness setting or the Qht’s backlight will stay on.
Table 3: Recommended Humidity Control Settings
Outside Temperature Relative Humidity Time Period Dehumidification Time
Below 80° F (27°C) 75-85% 12 hours 10 minutes
Above 85% 8 hours 20 minutes
80° - 90° F (27°- 32°C) 75-85% 10 hours 30 minutes
Above 85% 6 hours 40 minutes
Above 90° F (32°C) 75-85% 8 hours 40 minutes
Above 85% 6 hours 60 minutes
WARNING
During this test, low- and high-pressure faults are ignored. The system must be monitored closely during this test, and
the system must be shut down immediately if pressures exceed 425 psi for R-417A or 575 psi for R-410A. The system
should only be operated for a brief period of time if pressures fall below 30 psi for R-417A or 60 psi for R-410A.
WARNING
During this test, low- and high-pressure faults are ignored. The system must be monitored closely during this test, and
the system must be shut down immediately if pressures exceed 425 psi for R-417A or 575 psi for R-410A. The system
should only be operated for a brief period of time if pressures fall below 30 psi for R-417A or 60 psi for R-410A.

Programmable Functions Q3 and Qht Controls for Direct Expansion Systems
12 L-2516 ENGLISH
19: Cool-Only Mode
(Factory Default: HP)
You can select Heat Pump or Cool-Only operation. Select “HP” and the unit will operate in the default Heat Pump Mode, which
allows for cooling, reverse cycle heating and (optional) electric heat modes. Select “CL” for cool-only operation and the unit will
operate in Cooling or (optional) electric heat modes.
.
20: High Pressure Delay
(Factory Default: 3 minutes)
This function is used when the standard 3-minute delay during the high pressure fault routine requires an extended delay. The
delay can be increased up to 5 minutes between high-pressure-fault off cycles.
21: Anti-Icing Routine Adjustment
(Factory Default: 70°F)
The anti-icing routine prevents ice build up on the evaporator coil during extended periods of cooling operation. Installation
variables such as grille sizes, length of ducting, insulation, and ambient temperatures determine the run time required to
achieve set point. Factors that substantially increase run time include operating the system with hatches and doors open, and
programming an unrealistic set point (e.g. 65°F/18.3°C). Such situations can cause the evaporator to form ice on warm humid
days.
This function is used during cooling operation to allow any ice that may have formed on the evaporator coil to melt when the
cabin temperature drops below 70°F (default). This routine works in 10-minute cycles during which time the compressor cycles
off for 15 seconds for each degree the ambient-temperature is below 70°F (default) and runs during the rest of the 10-minute
cycle. For example, if the inside temperature is 67°F, the compressor will shut off for 45 seconds (3 x 15 seconds), and then run
for nine minutes and 15 seconds (10 minutes minus 45 seconds), repeating in 10-minute intervals. You may adjust the cabin
temperature at which the Anti-Icing routine is initiated. The range of adjustment is 65°F to 80°F.
22: Fan Speed Division
(Factory Default: 5)
You can select either 5 or 3 fan-speed divisions based on the Fan Response Differential (see Programmable Function “4: Fan
Response Differential” on page 9). The default is set at 5 fan-speed divisions.
•Q3 - Displays either the individual High, Medium and Low fan-speed LEDs if 3 speeds are selected, or a combination
of the High, Medium and Low fan-speed LEDs if 5 speeds are selected, for example:
• Low Speed = Low LED
• Medium Low Speed= Medium and Low LEDs
• Medium Speed = Medium LED
• Medium High Speed = Medium and High LEDs
• High Speed = High LED
•Qht - Displays 5 bars to indicate the five distinct speed changes or groups the bars to show three distinct speed
changes.
23: Aux Heat Enabled/Disabled
(Factory Default: “- -” Disabled)
The control allows operation of an optional auxiliary (aux) electric heater. The default for this feature is “- -” indicating disabled.
If an aux heater upgrade kit is installed, change this setting to “h1”. Selecting “h1” allows the electric heater to be operated
independently of the reverse-cycle heating and never at the same time.
.
NOTE
If you select “CL” Cool-Only mode, a 2-minute compressor delay will initiate whenever the compressor shuts down on
set point, a fault, or a power outage. The two minute delay will begin immediately after compressor shuts down. The
display will show the remaining time delay countdown at two second intervals when compressor is called to operate
within the two minute countdown period. If the two minute delay period has passed before the compressor is called to
operate, the compressor will come on with no delay.
NOTE
If you enable the aux heat function (“h1”), the fan will delay turning off for 30 seconds to allow the electric heater to
cool down. The delay occurs when the electric heater cycles off after set point is reached or when the mode is
changed.

Q3 & Qht Controls for Direct Expansion Systems Programmable Functions
L-2516 ENGLISH 13
24: Seawater Low Limit Adjustment
(Optional; Factory Default: 40°F)
If the optional seawater sensor is connected to the control board, this feature allows the system to switch from reverse-cycle
heat to electric heat (if an auxiliary electric heater is installed and enabled) if the seawater temperature drops below 40°F
(4.4°C) (default) and the reverse-cycle heat has operated more than five minutes. Once the seawater rises 3°F above the
Seawater Low Limit temperature, the system returns to reverse-cycle heating. If an aux heater is not installed, the system will
shut down and flash “LO” then “SE” when the seawater drops below 40°F (4.4°C) (default). Once the seawater rises 3°F above
the Seawater Low Limit temperature, the system goes back into reverse-cycle heating and stops flashing “LO” then “SE”. The
range of adjustment is 35°F to 50°F.
25: Humidity Sensor Limit Adjustment
(Optional; Factory Default: 60%)
If the optional humidity sensor is connected to the control board, this feature allows the system to dehumidify with electric heat
(if electric heat is installed and enabled) when the cabin humidity rises above 60% (default) relative humidity (RH). When the
room temperature has reached the set point, the compressor will turn off. The display will indicate that the system is in
"Dehumidify" mode. If the temperature decreases by one degree, the electric heat will turn on to maintain the set point. If the
temperature increases back to set point, the electric heat will turn off. If the temperature increases one degree above the set
point, the compressor will then turn back on. This operation will continue until the cabin’s relative humidity is less than 60%
(default). If an electric heater is not installed, the compressor run time will extend by operating to 1°F lower than set point. This
cycle continues until the cabin’s relative humidity is less than 60% (default). The range of adjustment is 50% to 80% RH.
26: Air Filter Timing Setting and Reset
(Factory Default: 0)
Use this feature for a reminder to clean or replace the unit’s air filter. Select the number of operating hours until the filter
reminder appears in the display flashing “Ar” then “FL”. The value entered represents that number times 100 hours. Function
values are between 1 (100 hours) and 25 (2500 hours). Dometic recommends that you check the air filter at least every 500
hours of operation. The default setting is off, designated with “00”. To reset the timer and stop the flashing filter reminder, press
the FAN, UP, and DOWN buttons simultaneously.
27: Select FAMU Operation (future feature)
28: CAN Bus Unit ID
(Factory Default: 59)
This feature allows all units with a CAN Bus adapter installed to be networked together to communicate with each other or the
ship’s CAN Bus system (with additional translator equipment in some cases). Enter the unit’s CAN Bus Unit ID number.
29: CAN Bus Group ID
(Factory Default: 58)
This feature allows all units with a CAN Bus adapter installed to be grouped together in a network system and communicate with
the ship’s CAN Bus system (with additional translator equipment in some cases). Enter the unit’s CAN Bus Group ID number.
30: Custom Medium Fan Speed (only with U-Board platform)
(Factory Default: 2)
You can set the number of fan speeds that can be modified by selecting either 2 or 5 speeds (if function 22, Fan Speed Division,
is set to 5). If function 22 is set to 3, the selection options for function 30 will be 2 or 3, and if 3 is selected, then function 32,
Medium Fan Speed, will be enabled. If function 22 is set to 5, you can modify 3 more fan speeds: Medium Low, Medium, and
Medium High, as functions 31, 32, and 33 are enabled.
31: Fan Speed Medium Low (only with U-Board platform)
(Factory Default: 50)
You can adjust the Medium Low fan speed to suit individual preferences. For instance, you may wish to decrease the Medium
Low fan speed setting in your stateroom to minimize fan noise.
32: Fan Speed Medium (only with U-Board platform)
(Factory Default: 62)
You can adjust the Medium fan speed to suit individual preferences. For instance, you may wish to decrease the Medium fan
speed setting in your stateroom to minimize fan noise.
33: Fan Speed Medium High (only with U-Board platform)
(Factory Default: 74)
You can adjust the Medium High fan speed to suit individual preferences. For instance, you may wish to decrease the Medium
High fan speed setting in your stateroom to minimize fan noise.

Programmable Functions Q3 and Qht Controls for Direct Expansion Systems
14 L-2516 ENGLISH
SUMMARY TABLE OF PROGRAMMABLE FUNCTIONS
Table 4: Programmable Functions - Ranges and Factory Defaults
Function
Number Description Factory Default
Custom
Settings Function Range
1Compressor Time Delay 0 0 - 70 seconds
2Display Fahrenheit, Celsius, or
Auto
F F, C, or A (only with U-Board)
3Compressor Differential 12 (12/8 = 1.5°F [0.8°C]) 2 - 31
4Fan Response Differential 8 (8/8 = 1°F [0.6°C]) 2 - 31
5Low Fan Speed 38 2 - 57
6High Fan Speed 85 41 - 99
7Fan Mode C (Continuous) C (Continuous)
I (Intermittent)
8AC Line Voltage Calibration -- Plus or minus 1%
9Temperature Calibration -- Plus or minus 1%
10 HU (Humidity) Pre-circulation 10 (minutes) 0 - 30 minutes
11 HU Dehumidification 30 (minutes) 10 - 60 minutes
12 HU Time Period 12 (hours) 2 - 16 hours
13 Software Revision (current version) n/a
14 Product Software dE = Direct Expansion
CH = Chilled Water or
Modulating Air Handler
n/a
15 Low-Pressure Switch Test OA = OK
FA = Fault
n/a
16 High-Pressure Switch Text OA = OK
FA = Fault
n/a
17 LCD or LED Segment Test Displays all LCD graphics or
LED segments
n/a
18 Sleep Mode
LCD backlight off or LEDs dim
On On = Continuous display
SL = Sleep Mode
19 Cool-Only Mode HP HP = Heatpump
CL = Cool Only
20 High-Pressure Delay 3 (minutes) 1 - 5 minutes
21 Anti-Icing Routine Adjustment 70 (°F) 65 - 80 °F
22 Fan-Speed Divisions 5 3 = 3 speeds
5 = 5 speeds
23 Aux Heat Enable/Disable “- -” “- -” = Aux Heat Disabled
“h1” = Aux Heat Enabled
(Reverse-cycle heat and aux heat
operate independently)
24 Seawater Low Limit Temp 40 (°F) 35 to 50 °F
25 Humidity Sensor Limit 60 (%RH) 50 - 80 %RH
26 Air Filter Timing Setting
(x100 hours)
0 0 = Disabled
1 - 25 (100 - 2500 hours)
27 Select FAMU (Fresh Air Make-
Up) Operation (future feature)
“- -” “- -” = Normal
FA = FAMU
28 CAN Bus Unit ID 59 0 - 99
29 CAN Bus Group ID 58 0 - 99
30 Custom Medium Fan Speeds 2 (only with U-Board) 2 or 5, or 2 or 3
31 Medium Low Fan Speed 50 (only with U-Board) 2 - 99
32 Medium Fan Speed 62 (only with U-Board) 2 - 99
33 Medium High Fan Speed 74 (only with U-Board) 2 - 99

Q3 & Qht Controls for Direct Expansion Systems High-Pressure Shutdown (HI / PS)
L-2516 ENGLISH 15
FAULT AND ERROR MESSAGES
To protect the equipment, certain fault conditions trigger a shutdown, and the system will not restart until the fault is repaired.
If an operational failure occurs, the display will flash one of the following fault or error code messages. Fault code displays are
canceled by pressing the MODE button (Q3) or POWER button (Qht)..
HIGH-PRESSURE SHUTDOWN (HI / PS)
The high-pressure switch is monitored by the control board. The high-pressure switch opens when the discharge pressure rises
above a preset maximum limit. The high-pressure fault routine operates differently in the Cool and Heat Modes.
INCOOL MODE
In Cool Mode, if the high-pressure switch opens, the control board will attempt three restarts and display a three-minute
countdown between restarts before it shuts down the entire system. The display will alternately flash “HI” and “PS”. This is a
sustained shutdown, and even when the pressure lowers after shutdown, the system will remain off until reset by pressing the
MODE button (Q3) or POWER button (Qht).
INHEAT MODE
In Heat Mode, if the high-pressure switch opens, the control board will shut down the compressor for three minutes. The display
will alternately flash “HI” and “PS” while the fan continues to run, allowing the heat in the coil to dissipate. This prepares the
system for recycling in the Heat Mode. The compressor will then continue to cycle, based on input from the high-pressure
switch, until the cabin temperature reaches set point, after which compressor cycling is automatically restored to normal
operation.
LOW-PRESSURE SHUTDOWN (LO / PS)
When the optional low-pressure switch is installed, it is monitored by the control board. The low-pressure switch opens when
the suction pressure drops below a preset minimum limit. The low-pressure fault routine operates differently in the Cool and
Heat Modes.
INCOOL MODE
In Cool Mode, if the low-pressure switch opens, the unit will first run for two minutes then shut down for 50 seconds. It will do
this four times. If the switch has not closed, the unit will shut down for 15 minutes, and the display will alternately flash “LO” and
“PS”. After 15 minutes of shut down, the cycle starts again, in which the unit runs for two minutes and then shuts down for 50
seconds.
If, after 8 attempted compressor starts, the low-pressure switch does not stay closed, the unit will go into a sustained shutdown
and the display will alternately flash “LO” and “PS”.
If the low-pressure switch closes at any time before the sustained shutdown, the unit will then operate normally.
INHEAT MODE
In Heat Mode, if the low-pressure switch opens, the fan will automatically change to low speed to try and raise system pressure.
It will run for 11 minutes in this mode. Note that the fan speed can not be adjusted during this time. Any attempt to raise fan
speed will result the display alternately flashing “LO” and “PS” while the unit continues to run.
After 11 minutes, the unit will run for two minutes, then shut down for 50 seconds. It will do this four times. If the switch has not
closed, the unit will shut down for 15 minutes, and display will alternately flash “LO” and “PS”. After 15 minutes of shut down, the
cycle starts again, in which the unit runs for two minutes and then shuts down for 50 seconds.
If, after 8 attempted compressor starts, the low-pressure switch does not stay closed, the unit will go into a sustained shutdown
and the display will alternately flash “LO” and “PS”.
If the low-pressure switch closes at any time before the sustained shutdown, the unit will then operate normally.
LOW-VOLTAGE SHUTDOWN (LO / AC)
The low-voltage protection feature is always active. If AC line voltage drops and remains below the limit (90 volts for a 100V
system, 100 volts for a 115V system, or 200 volts for a 230V system) for more than three minutes, the control shuts down the
entire system. The display will alternately flash “LO” and “AC”. This is a sustained shutdown, and the system will not resume
operation even if the line voltage returns to normal levels. To reset, press the MODE button (Q3) or POWER button (Qht).
For the low-voltage shutdown function to work properly, the control board internal voltmeter should be calibrated. This should be
done when the system is installed. To check or recalibrate line voltage, see “8: AC Line Voltage Calibration” on page 10.
NOTE
Your system must be equipped with the optional high-pressure switch and low-pressure switch for the high- and low-
pressure shutdown to operate. Check with your dealer to make sure these important protective devices are installed
properly.

Summary of Fault Codes and Indicator Codes Q3 and Qht Controls for Direct Expansion Systems
16 L-2516 ENGLISH
SUMMARY OF FAULT CODES AND INDICATOR CODES
INITIAL SYSTEM START UP
1. Open the seacock (seawater inlet valve).
2. Turn on the circuit breaker for the air conditioner. If a pump relay is installed, the breaker for the pump must also be
turned on.
3. Turn the control on.
4. Use the control to set the system for cooling or heating and adjust the set point temperature so the unit will turn on.
Table 5: Fault-Code and Indicator-Code Descriptions and Results
Code Description Result
LO / AC Operating voltage remained below acceptable limit for 3 minutes or more (100V for a
115V system or 200V for a 230V system).
Shutdown
HI / PS Head pressure above maximum preset limit. Indicates pump failure or loss of water
flow.
Shutdown
HP / - - High-pressure switch failed open or circuit wires open. Shutdown
LO / PS Suction pressure below minimum preset limit. Indicates loss of gas, or water too cold
for heating during Heat Mode.
Shutdown
LP / - - Suction pressure below minimum preset limit, failed low-pressure switch or circuit wires
open.
Shutdown
- - (flashing) Display connected to SMXII unit. The two components are not compatible. No Operation
IS / - - or - - Inside temperature sensor failure flashes IS / - - for 3 seconds if MODE button is
pressed. After 3 seconds, display shows constant - -. Cool or Heat Mode may be
selected for emergency operation and display will show a constant - -.
Emergency Operation
Ar / FL Display flashes Ar / FL for 15 seconds every 30 minutes indicating return air filter needs
to be cleaned or replaced. Reset and stop flashing by pressing the FAN, UP, and
DOWN buttons simultaneously.
Continue Operation
LC LC flashes momentarily if a button is pressed indicating the display is locked in current
mode of operation. Enter or exit lock mode by pressing the MODE, UP, and FAN
buttons simultaneously. UL flashes for 3 seconds when exiting lock mode.
Continue Operation
OU or Outside
/ 1st digit / 2nd
2 digits or OU
or Outside / - -
Displays the optional outside temperature as OU (Q3) or Outside (Qht) then the first
digit followed by second two digits. Displays OU or Outside / - - if optional outside
temperature sensor is not installed or failed open or shorted. See “Button Functions” on
page 6 for instructions.
Continue Operation
LO / SE After 5 minutes of compressor reverse-cycle heat operation, compressor shuts down if
optional seawater sensor is installed and temperature drops below 40°F (4.4°C). If an
optional electric heater is installed, operation switches from compressor reverse-cycle
heat to electric heater until seawater temperature rises above 43°C (6.1°C). Refer to
“24: Seawater Low Limit Adjustment” on page 13.
Shutdown or
Switch to Optional
Electric Heat.
SE or Water /
1st 2 digits
or SE / - -
Displays the optional seawater temperature as SE (Q3) or Water (Qht) then the first
digit followed by second two digits. Displays SE or Water / - - if optional seawater
temperature sensor is not installed or failed open or shorted. See “Button Functions” on
page 6 for instructions.
Continue Operation
HS / 1st 2
digits
or HS / - -
Displays the optional relative humidity as HS / then the first two digits of relative
humidty. Displays HS / - - if optional humidity sensor is not installed or failed open or
shorted. See “Button Functions” on page 6 for instructions
Continue Operation

Q3 & Qht Controls for Direct Expansion Systems General System Troubleshooting
L-2516 ENGLISH 17
5. Check for a steady solid stream of water from the overboard discharge. If more than one unit is installed, then check all
such discharges.
6. Verify that there is steady airflow out of the supply-air grille.
7. Allow unit to run for ten minutes at high fan speed. Check the temperature differential between discharge and return air
by placing an accurate thermometer in front of the discharge grill and then in front of the return air grill.
In Cool Mode the difference between the discharge and return should be 15 - 20°F (8.3 - 11.1°C), with normal ambient
air and water temperatures.
In Heat Mode the differential can be as high as 25°F (13.9°C).
If the unit does not appear to be operating properly, refer to the guidelines in “TROUBLESHOOTING” on page 17.
TROUBLESHOOTING
GENERAL SYSTEM TROUBLESHOOTING
Before you call for service, review this list. It may save you time and expense. This list contains common occurrences that are
not a result of defective workmanship or materials. If you need service after trying these procedures, call your nearest Dometic
dealer.
See additional troubleshooting information in the manual for your specific air conditioning system. See also “Digital-Controls
Troubleshooting” on page 20.
IMPORTANT
Do not turn the unit off then immediately turn it back on. Allow at least 30 seconds for refrigerant pressure to equalize.
Table 6: General System Troubleshooting
PROBLEM POSSIBLE REASON/SOLUTION
System will not start. 1. Air conditioner circuit breaker is off. Turn circuit breaker on at ship’s panel.
2. Digital control is not turned on. Press the Power button.
3. Wrong wiring at terminal strip. Check wiring diagram; correct if necessary.
4. Input-line voltage is insufficient. Check power source (shore/generator) for proper
voltage. Check wiring and terminals for proper sizes and connections. Verify with a
volt-meter that the power at the unit is the same as the power source.
5. Push-on connectors or butt splices became disconnected during installation.
Disconnect power supply and open electric box, check wiring diagram, correct if
necessary.
System runs continuously. 1. Set point temperature is improperly set: too low for cooling or too high for
heating. Raise or lower set point.
2. Porthole or hatches open. Close all port holes and hatches.
3. Improper air sensor location. Check your specific control troubleshooting section.
4. Seawater temperature too high for cooling or too low for heating. Seawater
temperature will directly affect the air conditioning unit’s efficiency. This air
conditioning unit can effectively cool your boat in water temperatures up to 90°F
(32.2°C) and heat (if reverse cycle option is installed) in water as low as 40°F (4.4°C).

General System Troubleshooting Q3 and Qht Controls for Direct Expansion Systems
18 L-2516 ENGLISH
Low airflow. 1. Airflow is blocked. Remove any obstructions in return-air stream. Clean return-air
filter and grille. Check for crushed or restricted ducting; ducting must be as straight,
smooth and taut as possible.
2. Fan Coil is iced. See below.
3. Fan speed is set to manual low. If the fan speed is set to manual low, press and
release the Fan button until the desired fan speed and airflow are reached. If you
want automatic fan speed control, press and release the Fan button until the letter “A”
displays.
Fan is not running. Check “Digital-Controls Troubleshooting” on page 20.
No cooling or heating. 1. Temperature set point is satisfied. Lower or raise set point.
2. Obstructed seawater flow. Clean seawater strainer. Check for obstructions at speed
scoop thru-hull inlet. Check for a good steady flow from the overboard discharge.
3. Seawater pump may be air-locked. Remove hose from pump discharge to purge air
from line.
4. Loss of refrigerant gas. Check air conditioning unit for refrigerant oil leakage, call
service technician.
5. Seawater temperature too high for cooling or too low for heating. Seawater
temperature will directly affect air conditioning unit’s efficiency. This air conditioning
unit can effectively cool your boat in water temperature up to 90°F (32.2°C) and heat
(if reverse-cycle option is installed) in water temperatures as low as 40°F (4.4°C).
6. Fan coil is iced (in cooling). Check your specific control troubleshooting section.
7. Fan is not running. Check your specific control troubleshooting section.
8. Control is in fan-only mode. Set system for Cool Mode or Heat Mode.
9. Seawater plumbing is air-locked. Ensure that seawater plumbing is installed per the
guidelines in this manual.
10. Digital control is programmed for Cool or Heat only. See “Digital-Controls
Troubleshooting” on page 20.
11. High-pressure switch is open (in cooling) due to improper seawater flow.
Strainer or intake may be plugged, seacock may be closed, check seawater hose for
kinks or collapses. Verify pump operation. Check pump circuit breaker if applicable.
12. High-pressure switch is open (in heating) due to improper airflow. Remove any
obstructions in return air stream. Clean return air filter and grille. Check for crushed or
restricted ducting, ducting must be as straight, smooth and taut as possible.
13. High-pressure switch is open (in heating) due to high seawater temperature.
System may cycle on high pressure if seawater temperature is above 55°F (12.8°C).
14. Compressor’s thermal overload is open due to either of the above reasons.
Compressor needs to cool down. Turn system off for a while (it may take up to three
hours to reset thermal overload).
No heating. Unit is in cool-only mode, or if reverse cycle, reversing valve may be stuck. Tap
reversing valve lightly with rubber mallet while unit is in heat mode. Call for service if that does
not correct the problem.
Table 6: General System Troubleshooting (continued)
PROBLEM POSSIBLE REASON/SOLUTION