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Modulating A/C Systems • Introduction
Warning
This manual contains essential information concerning
the safe and proper installation and operation of
your Cruisair air conditioning system. If there are
any statements or procedures in this manual that you
do not understand, contact the Dometic Applications
Department for assistance. Phone 804-746-1313
(8am - 5pm US Eastern Time), Fax 804-746-7248, or
email sales@dometicenviro.com, attention applications
department.
Notice
US federal law prohibits the intentional release of
refrigerant gases into the environment, including the
R-22 refrigerant used in most Cruisair air conditioning
systems. Special care must be taken when installing,
charging, and servicing Cruisair equipment to prevent
any loss of refrigerant. Only EPA certified technicians
with the proper equipment should perform service on
the refrigerant circuit of the system.
Drawings and Diagrams
The figures that are referenced throughout this manual can
be found immediately after the warranty section of the
manual. In addition, some Cruisair equipment will be shipped
with specific installation sheets or wiring diagrams that may
supercede the information located in this manual.
Air Conditioner Basics
The basic principle of an air conditioner is the movement of
heat. In a direct expansion (DX) water-cooled air conditioner,
heat is transferred from the cabin air to the refrigerant in the
cooling unit. The refrigerant is routed back to the condensing
unit where the heat is transferred to the seawater.
The heat exchange process relies on the movement of both
cabin air and seawater to work effectively. If airflow or
seawater flow is compromised, the efficiency of the system
will drop, and the unit could shut down on one of its safety
protection devices, or eventually become damaged.
Part of the cooling process, in addition to lowering the air
temperature, is the removal of moisture from the air. This
lowers the humidity, which makes the area feel more
comfortable, and helps keep the boat dry, reducing mold
growth and other moisture related problems.
L-0952 Introduction
The Effect of Seawater Temperature
The efficiency of the system is dependent on both the
seawater and cabin temperatures. The air conditioner works
best when the seawater temperature is below 90°F (32°C).
The unit will operate at higher water temperatures, but at
reduced capacity. As the water temperature rises, so does
the refrigerant pressure. A high-pressure safety switch will
shut the unit down if the water temperature gets too hot, or if
there is a loss of cooling water flow.
Warning
Do not operate your A/C 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.
The Modulating System
Unlike a standard DX remote condensing unit system, the
Cruisair modulating system allows independent thermostatic
control of up to five cooling units, all run by one compressor.
The FM type modulating condensing unit is cooling only. If
heat is desired, the cooling units should be ordered with the
optional electric heating element. One advantage to this is
that an individual unit can be in heating mode even when the
rest of the system is cooling.
How it Works in General
The Modulating System air conditioner consists of a special
condensing unit and multiple evaporators (cooling/heating
units), connected by copper refrigerant lines. The cooling/
heating unit, located in the cabin or area to be cooled,
consists of a blower, an evaporator coil and an optional
electric heater. Each area has an SMX microprocessor
control which allows independent control over that zone.
The condensing unit, located in the engine room or machin-
ery space, consists of a compressor, seawater condenser,
compressor relay, and other electrical and refrigeration
components.
Refrigerant lines connect the condensing unit to each
cooling unit, and a pair of signal wires run from each cooling
unit to the compressor relay on the condensing unit to signal
the compressor to run.
The cooling/heating unit blower draws warm humid cabin air
across the fins on the evaporator where the heat from the air
is transferred to the refrigerant in the evaporator coil. As this
happens, moisture in the air is captured on the evaporator
coil in the form of condensation and drips into the base pan.
As the refrigerant absorbs the heat from the cabin air, it
evaporates from a liquid into a gas. The compressor then
compresses the hot gas and pumps it through the outer tube
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