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 +1 954-973-2477.
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 IT WORKS
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.
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