Compact Marine Air Conditioner. How compact?

Compact marine air conditioner, is the ”original” marine AC unit.

It has features that other ACs (except 12 volt air conditioners) don’t on marine applications.

We’ll go through the details now,


Compact marine AC has these general traits;

  • size ranges from 3,500 BTU/hr, up to 27,000 BTU/hr for larger units

  • compact marine air conditioner also comes with the option of heating.

    Heating can be through an electrical strip (electric resistance coil), and/or through heat pump.

    Yes, some manufacturers provide both heating methods in a single package for better temperature control

  • either scroll or rotary compressor is used in compact marine air conditioner

  • one of most prominent factor in marine air conditioning is corrosion protection.

    Therefore, these units are built with corrosion resistant material, from stainless steel chassis up to the screws and necessary non metallic coating for important electrical component

  • air property controller, i.e. the thermostat for compact marine air conditioner comes in digital, or manual form

Compact marine air conditioner has these specific or special features compared to other marine AC units;

  • since it’s compact, a 2 ton sized compact marine air conditioner will only consume a space of, guess what…

    No bigger than 19 inches long, wide, and high

  • a feature that provides this ultra compact (yes, exaggerating can be addictive) size per heat capacity is the condenser coil.

    It is not a normal tube and fin condenser.

    In fact, it is “tube-to-tube” (or tube) heat exchanger, in coil shape.

    Coil arrangement can be horizontal, or vertical, or looped around the compressor to save space

  • it is not very heavy either – relatively.

    A 2 ton unit only weighs about 50 kg, which is about half of what a window air conditioner would weigh, at the same capacity

  • this AC type utilises blower at evaporator. Nothing surprising there.

    And the air direction can be varied by means of shroud positioning. Again, there is nothing surprising in that area.

    However, the uniqueness comes in the design of the shroud. It’s a simple circular, or oblong shape.

    The purpose of the design is to allow for duct attachment if you need central air conditioning.

    Otherwise, you can use it as it is, to cool a smaller space.

    So this AC can also function as central AC

  • compact marine air conditioner also comes in two package options.

    The options are self-contained and split unit.

    Yes, you can also have split, marine AC

  • sometimes you will discover that manufacturers use the term “direct expansion AC”

    It just means that the refrigerant evaporation is controlled through a TXV

Power option for compact units:

Unlike 12 volt air conditioners, the cousin – compact units, come in two designs. To run with,

  • direct power supply from generator or direct power supply (AC),

  • or to run with 12 volt power, through an inverter


Generally, you have to begin with,

  1. locating a suitable space for the AC,

  2. installing the AC unit and generator,

  3. installing the water pump unit, and its accessories,

  4. wire the AC to power supply, and check for correct operation,

  5. size and install the ducts (if you need any)

Specific installation steps vary slightly from a manufacturer to another, but there are common precautions to take when installing compact units;

  • scoop for sea water intake (for condenser cleaning) into hull section must face forward,

  • must, I repeat, must have a sea cock, or isolation valve between opening at the bottom of hull for water intake,

  • pump filter must be installed, and it must be installed between pump, and scoop,

  • please make sure that you apply marine sealant to external parts that come in constant contact with water or mist,

  • pump and filter must be placed below water level, to provide positive pressure for pump priming,

  • outlet water from condenser (discharge) must be higher than the suction,

  • please make sure that you eliminate kinks.

    Use elbows where necessary, and make sure suction line and discharge line follows the sloping requirement from the manufacturer

  • your diesel engine generator will emit CO (carbon monoxide) as part of its combustion by-product.

    Hence it is only necessary to install generator as far away as practical, from your room.

    A CO detector is a must. After all, the price is small compared to your life

So… what’s next?

Compact marine air conditioner is the most common AC used in marine transportation but let’s make some simple comparison with other marine ACs,

  • the price is about four times cheaper (size-to-size) than 12 volt air conditioner, and similar price to rooftop air conditioner (just the AC unit)

  • most compact of all marine AC (size-to-size). 12 volt portable AC is not a “real” AC

  • widely available in most marine stores

  • large range of cooling or heating capacity

  • reliability of 12 volt units, are not as good as the ”real” 12 volt air conditioner.

    “Real” 12 volt air conditioners can be started without and inverter, but not compact units.

    An inverter, is used to raise the starting power, and hence stresses the compressor during start up

All in all, compact marine air conditioner is a very attractive unit for air conditioning on water.

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