Split AC Unit
A split AC unit pairs an indoor evaporator with a separate outdoor condensing unit joined by refrigerant piping, conditioning one space such as the bridge or a cabin on its own circuit, in contrast to the ducted, multi-space reach of a central air handling unit.
Read more — Split AC Unit explained ▾
What defines this type
A split unit divides the refrigeration circuit across two boxes: an indoor evaporator, wall or ceiling mounted in the space it serves, and an outdoor or weather-exposed condensing unit connected by refrigerant pipe runs. Each split serves one space independently, so a fault on one unit does not take down cooling anywhere else, unlike a central AHU where a single fan or coil failure affects every space on that branch. This independence is why split units are common on the bridge, ECR and individual cabins where redundancy between spaces matters more than shared ductwork efficiency.
Main components
- Indoor evaporator unit – contains the evaporator coil, blower and filter, mounted directly in the conditioned space.
- Outdoor condensing unit – houses the compressor and air-cooled condenser coil, exposed to weather and salt spray on deck or in a vented enclosure.
- Interconnecting refrigerant pipework – liquid and suction lines running between indoor and outdoor units, a common leak point at flared or brazed joints.
- Expansion device – a capillary tube or thermostatic expansion valve metering refrigerant into the evaporator.
- Condensate drain – gravity or pumped drain removing water condensed off the evaporator coil.
Selection and sizing
Each space is sized independently against its own heat load, not a share of a building-style total. Points to confirm:
- Cooling capacity matched to the specific space's solar gain, equipment heat load and occupancy, since a bridge with large glazing runs hotter than a similarly sized cabin.
- Maximum allowable pipe run length between indoor and outdoor units, which limits how far the outdoor unit can sit from the space it serves.
- Ambient design temperature the outdoor unit must reject heat against, especially for units mounted on an exposed deck in tropical trades.
- Refrigerant type and charge, since longer pipe runs need additional charge beyond the factory pre-charge.
Regulations
Where refrigerant pipework passes through a fire-rated bulkhead or deck, the penetration must maintain the boundary's fire integrity, the same principle applied to AHU ductwork. Beyond that, split units carry fewer specific class requirements than a central system because each circuit is self-contained and does not distribute air between fire zones.
Typical faults
| Fault | Consequence |
|---|---|
| Refrigerant leak at a flared or vibration-fatigued joint | Gradual capacity loss and eventual compressor short-cycling on low pressure |
| Condensate drain blockage | Water overflow into the cabin or space below the indoor unit |
| Outdoor unit coil corrosion | Falling heat rejection and rising head pressure, worse the longer the unit sits in salt air without rinsing |
| Control board failure from humidity ingress | Erratic operation or total unit shutdown, common on units without a properly sealed control enclosure |
| Compressor short-cycling on low charge | Reduced compressor life and inconsistent room temperature |
What to look for in a supplier
- Marine-grade coil coating on the outdoor unit, not a standard shore residential coil.
- Documented maximum pipe run length and any additional charge calculation for longer runs.
- Indoor unit noise rating, particularly for bridge and cabin installations where quiet operation matters.
- Straightforward retrofit dimensions where the unit replaces an existing split without new ductwork.
Rinse outdoor coils with fresh water on a fixed schedule, not just when capacity starts to fall; salt loading on the fins is progressive and the unit is already down on performance well before it trips on high head pressure.
11 manufacturers · 771 models
Carrier Marine
160
Daikin Marine
128
Heinen & Hopman
96
Trane Marine
96
York/Johnson
96
Bronswerk Marine
64McQuay Marine
64Novenco Marine
64
Carrier
1- Outdoor coil corrosion
- Compressor overheating
- Expansion valve malfunction
- Wiring corrosion
- Compact split configuration saves deck space and isolates noise to the indoor unit
- Enhanced corrosion‑resistant coating on the outdoor coil extends service life in salty environments
- High efficiency operation with R‑410A refrigerant reduces fuel consumption
- Standard annual coil cleaning and gas‑charge checks simplify preventive maintenance
- Designed for marine installation with vibration‑isolated mounting points
- Outdoor coil can still corrode over time if protective coating is damaged
- Compressor may overheat in very high ambient temperatures or when airflow is restricted
- Expansion valve failures have been reported under rapid load changes
- Wiring corrosion risk in harsh marine atmospheres requires diligent inspection
- Limited cooling capacity (5 kW) may be insufficient for large passenger or cargo spaces
Daikin
1- Refrigerant leak at flare joints
- Indoor fan motor failure
- PCB corrosion from salt air
- Condensate drain blockage
- Compact split layout saves deck and interior space
- Low‑global‑warming‑potential R‑32 refrigerant improves environmental compliance
- Marine‑grade protective coating mitigates salt‑air corrosion
- Suitable for single‑zone accommodation or control‑room cooling
- Reported refrigerant leaks at flare joints require careful installation and periodic checks
- Indoor fan motor failures have been noted in service bulletins
- PCB corrosion can occur if coating is damaged or maintenance is lax
- Condensate drain blockage is a common maintenance issue
Mitsubishi Electric
1- Outdoor unit corrosion
- Compressor failure from liquid slugging
- Remote controller malfunction
- Drain pump failure
- High energy efficiency thanks to low‑global‑warming‑potential R‑32 refrigerant
- Compact split layout saves deck space and allows flexible placement of indoor unit
- Anti‑corrosion coating on outdoor module extends service life in salty environments
- Relatively quiet operation suitable for crew cabins and bridge areas
- Filter access is simple, supporting the recommended bi‑weekly cleaning schedule
- Outdoor unit still prone to corrosion if coating is damaged or maintenance lapses
- Compressor can be vulnerable to liquid slugging if condensate drainage is inadequate
- Remote controller may develop intermittent faults under vibration
- Drain pump failures have been reported, requiring spare parts on board
- Limited 3 kW capacity may be insufficient for larger accommodation blocks or high‑heat zones