SMB Air Conditioner
12 VDC Owner’s Manual 9/09
Page 5 of 13
Chapter 3 - General Description
The 12 VDC air conditioner built by Marvair® are self-contained, water-cooled units designed for use
with either fresh or seawater. The SMB models are designed to be used with a wall mounted thermostat
and use R-134a refrigerant.
Operating Ranges
The air conditioner is designed to work over a wide range of conditions. Among the most important
factors that affect the performance of the unit are inlet water temperature, inlet (return) air temperature
and the humidity of the inlet (return) air. Please consult your Marvair Marine dealer or the factory if you
have a question about the operation of your air conditioner.
Electrical
The SMB model is designed to operate of a nominal 12 volt DC power supply - an inverter is not
required. The unit will operate on a DC voltage from 9 volts to 17 volts.
General Operation
The 12 VDC air conditioner uses R-134a refrigerant in a conventional vapor compression cycle to
transfer heat from the air in the boat to the water. In the cooling mode, a blower blows the cabin air
through the indoor or evaporator coil where it is cooled and dehumidified. Liquid refrigerant passing
through the evaporator is boiled into a gas by heat removed from the air. The warmed refrigerant gas
enters the compressor where its temperature and pressure are increased. The hot refrigerant gas travels to
the water coil or condenser where it is cooled by the water and condenses to a liquid. Liquid refrigerant is
metered back into the evaporator coil to repeat the process.
