How It Works 1

Safety Considerations 1-2

Definition of Terms Used in this Manual 2-4

Electrical Grounding and Bonding 5

3 Phase Notice 5

Condensing Unit and Electric Box 6

Air Handlers 6

Mounting Digital Air Handler Controls 6

Ducting 7-8

Supply and Return Air Grilles 8

Sizing of Ducting and Grilles for Draw Thru Air Handlers 8

Draw Thru Air Handlers 9

Blow Thru Air Handlers 10

Slim Line Air Handlers 11

Condensate Drains 12

Sea Water Pump 12

Sea Water Plumbing 12-13

Sea Water & Chilled Water Manifold Sizes 14

Chilled Water Circulation Circuit 14

Recommended Pipe Size vs. System Capacity 14

Circulation Circuit Pressure 14

Typical Chilled Water System Installation Diagram 15-16

Chilled Water Pump 17

Suggested Piping to Air Handlers 17

Fresh Water Fill System 17

Insulation 18

Piping Installation 18-19

Miscellaneous Optional Components 19

Flushing the Circulation Circuit 19

Filling & Purging the Circulation Circuit 20

Generic Wiring Diagram for Line Voltage MCW System 21-22

See manual binder and chiller electrical box for unit specific wiring diagram.

Thermostat Set Points 23

Timers 23

High Limit Switches and Freeze Stats 23

Flow Switches 23

Start-Up of the System 23

Maintenance 24

Routine Maintenance 24-25

Extended Maintenance 25-26

Winterization 26

Sea Water Condenser Coil Cleaning Procedure 27

Trouble Shooting Guidelines 28-29

How to Diagnose Control Circuit Components 30

Manufacturer's Limited Warranty Agreement 31

System Specific Settings 32

Maintenance Record 32


Congratulations on the purchase of your air conditioning chilled water system. No matter which of the following features was the reason you purchased this chilled water system we are sure it will meet your needs and will give you many years of efficient and trouble free use.

The chiller series of staged chilled water systems are designed for boat applications starting at approximately 40 foot in length. They are available in capacities from 24,000 to 600,000 BTU's and voltages of 208, 230, and 460 volt 60 hertz and 220 or 380 volt 50 hertz, single or three phase. These systems can provide ideal solutions for problems of space requirements, amperage consumption and weight for both new boat and retrofit applications and are designed for marine applications incorporating the following features:



  • Compressors offering reduced amperage draw, up to 25% less than conventional units


  • Stainless steel brazed plate chilled water heat exchangers


  • Remote mountable electrical box


  • Pre-charged and pre-wired systems for easy field connections


  • Charge Guard protection to insure refrigerant integrity during handling and installation


  • Light weight aluminum construction for corrosion protection


  • Control circuit provides multiple fail-safes for system protection

This manual is intended to provide the information necessary to ensure proper operation and maintenance of the chiller series units. Misunderstood operating procedures can result in unsatisfactory performance and/or premature failure of these units, so before proceeding please read this manual completely.

The chiller series units are covered under the existing Marine Air Systems warranty policy contained in this manual. In the interest of product improvement, Marine Air Systems' specifications and design are subject to change without prior notice.


Marine Air Systems (MAS) is a manufacturer of air conditioning and refrigeration equipment for the marine industry. MAS is committed to innovative technology, competitively priced products and market leadership. The MAS team has many years of experience in the design, manufacture, application and support of marine air conditioning and refrigeration. Our practical experience and design capability allows our application engineers and customer support team to offer optimum solutions for your environmental control requirements.

Dear Customer:

Please contact the engineering department at Marine Air Systems with any comments or suggestions for improving this publication, your input would be appreciated. Our address and phone numbers are printed on the back cover of this manual.


Your chilled water air conditioning system consists of the chiller condensing unit, air handlers installed throughout the vessel, fresh water piping connecting the chiller to the air handlers, and the sea water system. The chiller condensing unit consists of three major components: the compressors, the "tube in tube" condenser coils and the evaporators (or heat exchangers). The chiller system is charged with a refrigerant which circulates throughout these components. The air handlers consist of two major components: the blower and a coil. Fresh water circulates through the piping from the chiller to each air handler and back.

In cooling mode, warm cabin air is drawn (or blown) across the air handler coil by the blower. Removing heat from the cabin air cools it and the cooled air is blown back into the cabin. The heat from the cabin air is transferred to the fresh water circulating through the coil. The warmed water is pumped back to the chiller. The water is circulated through the chiller evaporators where the heat is transferred to the refrigerant in the evaporator coil, thus cooling the "chilled" water. The "hot" gas is then circulated through the outer tube in the chiller condenser coils. Sea water is circulating through the inner tube of the condenser coils via the sea water system. The heat is transferred from the refrigerant to the sea water and pumped overboard taking the original cabin heat with it. The chilled water (not sea water) is then pumped back through the piping to the air handlers in a continuous loop as the cycle repeats.

If the vessel is heated, it is either by reverse cycle or electric heat. Each method pumps warm water from the chiller to the air handlers. For reverse cycle heating, the chiller refrigerant flows in the opposite direction through a reversing valve, thus adding heat to the fresh water loop, instead of removing it as in the cooling mode. Electric heat systems use a heater barrel to warm the fresh water. Some systems also use "chill chasers" which are electric heating coils built into the air handlers that warm the air directly.


Installation and servicing of this system can be hazardous due to system pressure and electrical components. Only trained and certified service personnel should install, repair, or service equipment. When working on this equipment, always observe precautions described in the literature, tags, and labels attached to the unit. Follow all safety codes. Wear safety glasses and work gloves and place a fire extinguisher close to the work area.

Never install your air handlers in the bilge or engine room areas. Insure that the selected location is sealed from direct access to bilge and/or engine room vapors. Do not terminate condensate drain line within four (4) feet of any outlet of engine or generator exhaust systems, nor in a compartment housing an engine or generator, nor in a bilge, unless the drain is connected properly to a sealed condensate or shower sump pump.

Danger! Electrical shock hazard. Disconnect voltage at main panel or power source inlet before opening any cover. Failure to comply may result in injury or death.

Warning! To minimize the hazard of electrical shock and personal injury, this component must be effectively grounded. Refer to installation guidelines for further information.


Notice: This component is charged with a HYDROCHLOROFLUOROCARBON (HCFC) refrigerant R22. Effective July 1, 1992 it shall be unlawful for any person to knowingly vent or otherwise knowingly release any class I (CFC) or class II (HCFC) substance as a refrigerant in a manner which permits such substance to enter the atmosphere per the clean air act of 1990. Public law 101-549 title IV section 608-C. Failure to comply may result in severe penalties, including fines and imprisonment.


AIR HANDLER: The fan coil unit that circulates air into a specific area for heating or cooling. Three types of air handlers are available:

Draw Thru - An air handler with the fan positioned to pull or draw air from the cabin across the air handler coil and deliver the conditioned air through duct work back into the cabin.

Blow Thru - An air handler with the fan positioned to push or blow cabin air across the air handler coil directly into the cabin. No duct work is used on this type of air handler.

Slim Line - A modular blow thru air handler with interchangeable panels for alternate supply and return air locations. Duct work may be used on this type of air handler, however it must be a short plenum with the same size as the supply air opening in the unit to a same sized grille.

BLEEDER PORTS: Capped ports connected to 1/4" flexible tubing located on the air handlers for purging air from the chilled water circulation system.

BONDING: In the vessel's electrical system, any metal that might come into contact with salt water is connected to the bonding circuit to help alleviate the effects of electrolysis (follow ABYC standards).

BTU: (British Thermal Unit) A common term used to define and measure capacity or refrigeration effect.

CFM: Abbreviation for "cubic feet per minute", a term used to specify the amount of air flow through the air handlers and ducting.

CHILL CHASER: An auxiliary electric heater located in the air handler.

CHILLED WATER CIRCULATION CIRCUIT: Supply and return piping from the chiller to the air handlers. The supply piping carries chilled water (in cool mode) from the chiller to the air handlers. Return piping carries warmed water (in cool mode) from the air handlers back to the chiller. The supply and return piping form a continuous closed loop.

CHILLED WATER CIRCULATION PUMP: A centrifugal pump used to circulate the fresh water between the chiller and the air handlers for heat transfer. Since this pump is located in a "closed loop" system, it does not need to be installed below the water line of the vessel. Whereas the sea water pump does need to be installed below the water line.

CIRCUIT BREAKER: An electrical device which provides high current and short circuit protection for the compressors and pumps used in the chiller. HACR (heating, air conditioning & refrigeration) type circuit breakers are recommended for the ship's panel. HACR circuit breakers have a long delay to compensate for the electrical surge associated with compressors.

COMPRESSOR: An electrical motor/pump that draws cool, low pressure refrigerant gas and compresses the gas into a hot, high pressure gas.

COMPRESSOR OVERLOAD: An electrical device used to protect the compressor from excessive heat or current draw.

CONDENSATE DRAIN PAN: The pan directly under the air handler's coil for removal of the "condensed" moisture taken out of the cabin air. Two drain spud attachments are provided for connection to drain hoses for proper removal of the water to a sump. There is also a condensate drain pan located under each chiller and the chilled water pump.

CONDENSER: The heat exchanger through which heat is transferred between the refrigerant in the chiller and the sea water flowing through the coils and manifold.

ELECTRIC HEAT: Electric resistance heaters are used as a chill chaser in the air handlers to warm the air, or in the chiller heater barrels to warm the circulating water, in heat mode.

EXPANSION TANK: A container housing a diaphragm (20 psig) to cushion against any water hammer in the circulation system piping. It also provides for expansion of the water volume as the water is heated.

FAN SPEED CONTROL: An "on/off" switch that also regulates the amount of voltage supplied to the fan motor, thus controlling the speed at which the motor turns.

FLOW SWITCH: A control device located on the chilled water supply side of each of the brazed plate heat exchangers that prevents the system from operating until water flow has been established, and turns the system off if the water flow is insufficient.

FREEZE STAT: A low temperature thermostat used as a control device to sense chilled water temperatures and shut the entire condensing unit off when supply water temperatures in the circulation piping system reach 38F. This prevents the possibility of rupturing the chilled water evaporator coil, as well as any other piping in the system, due to the water freezing.

FRESH WATER FILL SYSTEM: Components installed on the return line to the chiller for filling the circulation circuit piping system.

GPM: Abbreviation for "gallons per minute", a term used to specify the amount of water flow through the chilled water or sea water system.

HIGH LIMIT SWITCH: A high temperature thermostat used as a safety device to shut down the condensing unit when the water temperature in the circulation piping circuit reaches 120F. This prevents the possibility of damaging any PVC piping or any other components due to the water getting too hot.

HIGH/LOW PRESSURE SWITCHES: Electrical control devices operated by high and low side system refrigerant pressures respectively. If pressure is too high (425psig) or too low (35psig) the appropriate switch automatically opens the electrical circuit and shuts down the respective compressor. These switches reset automatically.

MOTORIZED WATER VALVE: An electrically operated 3-way water regulating valve on an individual air handler controlled by the thermostat. This valve provides water flow through the air handler when opened, and bypasses water flow from the supply side to the return side when closed.

PUMP RELAY PANEL (PRP): Used with more than one chiller, the PRP is a circuit board module wired between the chillers and the chilled water or sea water pump (one PRP for each pump). When any of the chillers is turned on to heat or cool both PRPs are energized and switch each pump on. Each PRP should have its own circuit breaker sized for the pump, but not to exceed 20 amps.

REVERSING VALVE: (on reverse cycle units only) An electromagnetically controlled valve that reverses the flow of refrigerant between the condenser and evaporator of the chilled water condensing unit, thereby permitting heat to be extracted from the cabin in the cooling mode and added into the cabin in the heating mode.

RUN CAPACITOR: An electrical storage device used to reduce amperage to some electric motors for more efficient operation.

SEA WATER PUMP: A pump and motor combination that provides a continuous water flow through the condenser coil(s). The sea water pump must be installed below the water line for proper operation.

SEA WATER STRAINER: A housing containing a screen made of metal nylon to filter out debris drawn into the sea water circuit that could foul up the sea water pump or piping. The strainer must located between the thru hull inlet and sea water pump.

START CAPACITOR: An electrical component that assists the compressor by releasing stored current during initial start up.

START RELAY: An electrical device that controls the duration of voltage supplied from the start capacitor to the compressor on start up.

THERMOSTAT: An adjustable control device which senses room temperature, via an air thermistor or sensor, and operates the motorized valve on an air handler for water flow.

THERMOSTATIC EXPANSION VALVE: A metering device used to convert high pressure liquid refrigerant to low pressure liquid refrigerant.

THRU HULL FITTING: There are two different thru hull fittings used in the sea water circuit. The speed scoop strainer inlet fitting is mounted below the water and serves as the inlet for the sea water circuit. The discharge thru hull fitting is mounted above the water line and serves as the outlet for the sea water circuit.

TIME DELAY RELAY: An electronic device used to delay and stage the starting of multiple compressors.

TON: In refrigeration/air conditioning, a ton is the amount of heat absorbed in melting a ton (2000 lbs) of ice over a 24-hour period. The ton of refrigeration is equal to 288,000 Btu in 24 hours. Divide 288,000 by 24 and get 12,000 Btu per hour. Therefore, one ton of refrigeration = 12,000 Btu/hr.


All chiller condensing units are supplied with a terminal strip mounted inside the electrical box. The electrical supply, ground wires, and pump circuits are all connected at this terminal strip. All units must be effectively grounded to minimize the hazard of electric shock and personal injury. The following are to be observed:

1. AC (alternating current) grounding (green wire) must be provided with the AC power conductors and connected to the ground terminal (marked "GRND") at the AC power input terminal block of the unit(s), per ABYC standard E-8, or equivalent.

2. Connections between the vessel's AC system grounding conductor (green wire) and the vessel's DC (Direct Current) negative or bonding system should be made as part of the vessel's wiring, per ABYC standard E-9, or equivalent.

3. When servicing or replacing existing equipment that contains a chassis-mounted "ground" stud, the service person or installer must check the vessel's wiring for the existence of the connection required in item 2 above.

ABYC standards are available from: American Boat and Yacht Council

3069 Solomon's Island Rd.

Edgewater, MD 21036 Telephone: (410) 956-1050

The condenser manifold comes equipped with a tab for wiring to the ship's bonding system. The chiller must be connected to the ship's bonding system to prevent corrosion due to stray electrical current or voltage. All pumps, metallic valves and fittings in the sea water circuit that are isolated from the unit by PVC or rubber hoses must be individually bonded to the vessels bonding system also. This will help eliminate any possibility of corrosion due to stray current or voltage.



For all three phase chilled water condensing units (power source is either 208/230 VAC/3 or 460/380 VAC/3), it is extremely important to insure that wiring and phase sequencing of the three phase power source is correct. Marine wiring standards call for power source phases L1, L2, and L3 to be color-coded BLACK, WHITE, and RED, respectively. These must be connected to the unit with the proper sequence. Otherwise, it will not operate properly. If the wiring sequence is incorrect, the units compressor (Scroll type only) and pump (if applicable) will run in the reverse direction at a significantly increased noise level. Reverse compressor operation will result in increased suction pressure and reduced head pressure, but it will not permanently damage any aspect of the unit. No cooling will be produced. If the circulating pump runs in the reverse direction, the closed water loop will not achieve high enough operating pressures and air can not be eliminated from the system. If the sea water pump runs in the reverse direction, it will not deliver adequate cooling water to the condenser. The electric heat may work properly, but reverse cycle heating will not.


The chilled water condensing units are designed to be installed below deck either in the engine room, machinery compartment, lazarette, or similar type area. They are unaffected by vibration, moisture or ambient temperatures up to 140F (60C). These units must be well secured on a sturdy, level surface with the two mounting brackets provided. The MCW Chiller must be installed so that it is accessible for service when required. Multi-stage chillers must have at least 12" of free space on the side for plumbing to the manifolds. The condensing unit is hermetically sealed and requires no ventilation for proper operation. Normal engine room temperatures will not affect operation of the condensing unit.

The electric box can either remain mounted on the chiller, as shipped from the factory, or remote mounted. Single phase units with Inertia compressors have position sensitive components in the electric box which must be mounted lid up, same as on the chiller. Three phase chillers or single phase chillers with Scroll compressors have electric boxes that can be remote mounted either vertically or horizontally. Remote mounted electric boxes must be secured to bulkheads or study frames.


Air handlers are designed in three types of configurations; blow thru, draw thru and slim line, to allow for diversity and flexibility in application. All types must be fastened securely and level for proper operation and condensation removal. All air handlers must have an unrestricted return air stream. Air handlers, and their return air inlets, must not be located in areas open to bilges, lazarettes, heads or other areas where fumes or odors can be introduced into the conditioned air supply.


Before mounting the air handler digital display panel touch pad, consider the location. The air sensor built into the display panel will provide excellent room air temperature sensing given a proper installation. The display panel should be mounted on an inside wall, slightly higher than mid-height of the cabin, in a location with freely circulating air where it can best sense average temperature. Do not mount the display in direct sunlight, near any heat producing appliances or in a bulkhead where temperatures radiating from behind the panel may effect performance. Do not mount the display above or below a supply or return air grille or in the supply air stream. Do not mount the display behind a door, in a corner, under a stairwell or any place where there is no freely circulating air. Mount the display within display cable length (custom lengths available) of the air handler. Plug the cable into the circuit board in the electrical box and into the back of the display panel. Secure the display panel to a bulkhead with the adhesive strips provided. Clean the mounting surface with isopropyl alcohol only prior to placement (test alcohol on hidden portion of surface first). If the adhesive strips cannot be used, use #6 truss head screws to mount the display. The panel has predrilled holes in each corner that can be accessed by peeling back the adhesive strips. Carefully & slowly drill 5/32" holes through the front of the lexan cover lining up with the predrilled holes in back. Do not use a screw gun and do not over-tighten screws when mounting panel. Over-tightening screws will damage the lexan cover. If a proper location for room temperature sensing cannot be found for the display, an optional remote air sensor may be used. Mount the remote air sensor in the return air stream behind the return air grille/opening and plug its cable into the appropriately marked socket on the circuit board. See appropriate air handler control manual for programming and operation.


Good air flow is critical for the performance of the entire system. It is highly dependent on the quality of the ducting installation. The ducting should be run as straight, smooth and taut as possible minimizing the number of 90 degree bends (two tight 90 degree bends can reduce airflow by 25%). The following table shows minimum duct diameters and their corresponding return and supply air grille areas in square inches. If a transition box is used, the total area of supply air ducts going out of the box should equal the area of the supply duct feeding the box. To calculate the square inch area of a round duct: divide the diameter by two to get the radius (r), multiply the radius by itself (r), and multiply that number by 3.1416 (). The following is a summary of proper ducting connections:

  1. Pull back the fiberglass insulation exposing the inner mylar duct hose.
  2. Slide the mylar duct hose around the mount ring until it bottoms out.
  3. Screw 3 or 4 stainless steel sheet metal screws through the duct hose into the transition ring. Make sure to catch the wire in the duct hose with the heads of the screws. Do not use band clamps, the mount rings are tapered and the hose will slide off.
  4. Wrap duct tape around the ducting and ring joint to prevent any air leaks.
  5. Pull the insulation back up over the mylar to the ring and secure with tape.

All ducting should:

  • Be appropriately sized for each application.
  • Run as smoothly and taut as possible.
  • Have as few bends or loops as possible.
  • Be securely fastened to prevent sagging during boat operation.
  • Have all excess ducting lengths trimmed off.
  • Not be flattened or kinked.
  • Insulated when located in high heat load areas (hull side, mechanical compartments, etc.).

The design of a proper supply ducting system in a boat begins with the outlet from the blower. The blower ring sizes used by MAS are designed to keep the air velocity and frictional pressure drop relatively low on the supply air side. Reducing the blower ring size will create higher air velocities. Higher air velocities will increase pressure drop and increase air flow noise. Increased pressure drop will reduce the overall air flow (CFM) and the heating or cooling capacity of the unit (BTU/hr). In order to keep the air to an acceptable velocity a ducting system should have the same cross sectional area as the blower ring. The following table shows the cross sectional area needed for each size unit as well as the size of the duct ring supplied on the unit.

Several circumstances may be encountered where a larger duct size may be needed to achieve the desired air flow for a particular unit. These include excessively long duct runs (greater than twenty feet), large numbers of bends in the duct runs (greater than 3-90 bends), or a transition box located at the outlet of the blower. In each of these cases a duct size one inch larger than that shown in the table above should be used.

MAS recommends that ducting not be used on the return air side of a unit. However, if the unit must be return air ducted, it is recommended that the return air duct size be at least one inch larger in diameter than the supply air duct size.

The recommended minimum duct length for a draw thru type air handler is five feet (1.52m). This length prevents motor noise or vane tip noise on the blower wheel from being audible in the cabin area. The maximum duct length of twenty feet (6.04m) should not be exceeded. These longer duct runs can prevent proper air flow delivery, causing poor operation and performance.

When using ducting transition boxes, the total outlet area should be at least equal to the inlet area.

Built-in air plenums should be constructed to deliver proper air flow and minimize air noise. Plenums should be fully pressurized by the air delivery through the duct work and incorporate diffusers when necessary to create an even flow across the entire surface of the supply grille or outlet. The cross sectional area of the plenum should be equal to, or slightly bigger than, the supply duct. Undersized plenums create air turbulence and generally cause "noisy" air delivery. Oversized plenums do not pressurize sufficiently and cause poor or no air flow. All air plenums must be thoroughly sealed to prevent air leakage. Plenums constructed of conductive materials must be insulated properly to prevent condensation and possible water damage. Wood is a conductive material and should be sealed to prevent delamination, and insulated where necessary.


The return air grille should be placed as close as possible to the air handler to maintain direct uninterrupted airflow to the coil. It should also be mounted as low as possible. The return air grille should not be located in such a way that the supply air blows directly into it. This will cause "short cycling" which results in poor performance and inadequate air conditioning. All return air grilles must have a filter attached to prevent dust or particle build up in the coil. If return air grilles are not used (i.e., louvered doors, hidden cut outs, etc.) a clip on filter should be attached to the air handler making sure that there is enough clearance for access to the filter for cleaning.

The supply air grille should be mounted as high as possible in the cabin to ensure proper air flow. This application permits air flow across the ceiling of the cabin and causes natural convection currents with the cool supply air falling, and forcing the warm air through the return air stream or up to the ceiling to mix with the cooler air being distributed. Failure to deliver the supply air high can result in stratification of the air in a cabin, causing cooler temperatures near the floor and warmer temperatures near the ceiling.

A.H. Unit BTU/hr 6000 7000 9000 12000 16000 18000 24000
Duct Diameter 5" dia 5" dia 5" dia 6" dia 7" dia 7" dia 8" dia


19.6 sq in 19.6 sq in 19.6 sq in 28.3 sq in 38.5 sq in 38.5 sq in 50.3 sq in

Air Grille

88 sq in 88 sq in 98 sq in 140 sq in 168 sq in 200 sq in 280 sq in
Supply Air Grille 35 sq in 40 sq in 50 sq in 70 sq in 84 sq in 100 sq in 140 sq in


These units are ductable air handlers with rotatable blower assemblies, providing diverse arrangements for supplying air to one or more cabins. They are designed to be installed low in a cabin area, under seats or berths, or in the bottom of lockers to maintain a return air stream close to floor level. Fastening the air handlers is accomplished through the four (4) mounting brackets provided. The blower assembly should be rotated, if necessary, to provide the most direct ducting run possible.


These units are nonductable air handlers designed to be installed high in a cabin area: at the top of lockers, bulkhead corners or overhead compartments. They can be fastened securely using the four mounting grommets located in the upper four corners of the mounting plate.

As no duct work is used, blow thru air handlers must be able to deliver air directly into cabin areas. They must be located against the inside of a bulkhead or partition common to the cabin to be conditioned. The supply air grille must be at least equal in surface area and dimensions to the coil.

If the air handler cannot be flush mounted against the bulkhead or partition, a plenum chamber can be attached between the face of the coil and the inside of the partition. This plenum must be equal or slightly larger than the coil surface, sealed completely, and be a short, straight run. Due to their design, the blow thru air handlers cannot be connected to excessively long plenums, multi-directional plenums, or any duct work.

The return air to a blow thru air handler is provided through a properly sized grille (at least equal to the size of the coil) located underneath, alongside, or behind the air handler. While this return air grille is located higher in the cabin and close to the air handler than a typical draw thru application, proper air circulation is still achieved.


Slim line air handlers are used in limited space situations. They are similar in application to the blow thru air handlers, however, slim lines can be mounted low in side panels and narrow bulkhead spaces. Currently, the slim line is constructed in two modules, the blower and the coil. The two modules can be configured horizontally or vertically. The horizontal configuration is used for overhead mounting and the vertical configuration is used for mounting behind bulkheads and panels. The return air grille must be the same size as on the unit. Slim line units can be ducted with the use of plenums. Follow the same guidelines for the blow thru units for plenum construction.


All units come with condensate drains. Under adverse climate conditions (for example, high humidity) condensate water could be produced at a rate of approximately one gallon per hour. With this in mind, it is important to route condensate drains aft and downward to a sump or overboard discharge, utilizing all standard practices for securing hoses and mounting thru-hull fittings. After the condensate installation is complete, test the installation by pouring a quart of water into the pan and checking for flow overboard. For installation of the condensate drain:

If dual drain fittings are used: These may be connected to a single condensation drain line, provided that a minimum 2" (5.08cm) drop exists from the base pan drains to the connection fittings.


The chillers condensing units are water cooled and require a properly sized sea water pump for operation. The sea water pumps are sized according to the BTU capacity of the chilled water unit. The sea water pump must be installed so that it is always at least one foot below the water line regardless of which tack the vessel is on. If the capacity of your air conditioning system is greater than or equal to 48,000 BTU/hr, the sea water pump is most likely air cooled and will need occasional oiling. See manufacturer's labeling on the pump for maintenance instructions.

IMPORTANT: Each pump relay panel (PRP) must have a dedicated circuit breaker sized for the pump but not to exceed 20 amps maximum.

IMPORTANT: Pumps greater than one horsepower (1HP) must be connected through a pump relay panel, this is true even for single stage units, because the chiller's HRC toggle switch cannot handle the amp load of a larger sea water pump.


Sea water temperature will directly affect the chiller's efficiency. This chiller can effectively cool your boat in water temperatures up to 90F and heat (if reverse cycle option is installed) in water as low as 40F. Use electric heat (if installed) in sea water temperatures below 40F.

INSTALL THE SEA WATER SPEED SCOOP INTAKE AS FAR BELOW THE WATER LINE AND AS CLOSE TO THE KEEL AS POSSIBLE IN ANY APPLICATION, BUT ESPECIALLY ON A SAIL BOAT, TO KEEP THE INTAKE IN THE WATER WHEN THE BOAT HEELS OVER SO THAT AIR DOES NOT GET INTO THE SYSTEM. A speed scoop should be utilized to insure positive water flow while the vessel is underway. The speed scoop must be installed facing forward and not be shared with any other pump. A full flow bronze sea cock (ball valve), connected directly to the speed scoop intake, must be used to be able to disrupt the incoming water to the sea strainer and pump should the need arise. The thru-hull, strainer, and hoses should be equal in size to the pump inlet. Bed the speed scoop and thru hull with a marine type sealant.

Since the sea water pump is centrifugal and not self-priming, it must be mounted so that it is always at least one foot below the water line regardless of which tack the vessel is on. The pump may be mounted horizontally or vertically, however the discharge must always be above the inlet. The pump head should be rotated toward the direction of water flow. It is recommended that all hose connections be secured by means of double/reversed stainless steel hose clamps. A sea strainer between the sea cock and pump is mandatory to protect the pump from foreign matter, such as seaweed. Not using a sea water strainer will void the pump warranty and jeopardize the entire system. The sea water system must be installed with an upward incline from the seacock through the strainer to the inlet of the pump and then up to the chiller condenser coil/manifold inlet.

From the discharge outlet of the pump, route the plumbing to the inlet connection on the condenser coil/ manifold. This hose should be plumbed as straight and smooth as possible, with no loops or vertical bends, so that it is self-draining and consequently self-purging. The discharge outlet of the condenser must be plumbed overboard using a discharge thru-hull located above the water line. The location selected for the overboard discharge thru-hull should be accessible for periodic visual inspection and as close to the water line as practicable to reduce noise. It is recommended that marine grade reinforced hose be used as well as double/reversed stainless steel hose clamps throughout the sea water system.

Follow these guidelines for installing the sea water system:


Chiller Capacity (tons) 4-10 11-18 19-33 34-50
Chiller Capacity (BTU/hr x 1,000) 48-120 132-216 228-396 408-600
Manifold & FPT Connection Size 1" 2" 2" 3"


The water circulation system is designed as a closed loop circuit connecting all air handlers to the chillers. Piping size and type is determined by the overall BTU capacity of the system and the type of heat used. For COOL ONLY systems use SCH 40 PVC minimum. For REVERSE CYCLE or ELECTRIC HEAT systems use SCH 80 PVC, CPVC or Copper Pipe. The following chart provides information for sizing the chilled water piping. Installing pipe that is too small will increase water velocities which may cause erosion of piping. Also, excessive water side pressure drops can occur which will reduce the water flow to the air handlers resulting in reduced performance. See pages 15 & 16 for a typical chilled water and sea water systems installation diagram.

Capacity (BTU/hr x 1,000) 4-21 24-45 48-81 84-129 132-225 228-405 408-600
Tons 0.33-1.75 2-3.75 4-6.75 7-10.75 11-18.75 19-33.75 34-50
GPM 1-5.25 6-11.25 12-20.25 21-32.25 33-56.25 57-101.25 102-150
Nominal Pipe Size " 1" 1" 1" 2" 2" 3"

If individual piping runs exceed fifty feet (15.24m), the next larger pipe size is recommended, this will help reduce the pressure drop through the system. The "System Capacity" listed in the chart above is measured at any given point in the chilled water loop. Size the piping according to the total capacity of air handlers fed from that point. Counter flow piping of the supply and return lines from the chiller will assure equal water flow through all air handlers (i.e., the air handler closest to the chiller will have the shortest length of supply water piping and the longest length of return water piping and vice versa). Excessive pressure drops between air handlers will be eliminated with this type of piping arrangement. Ends of main and branch chilled water lines should be extended and capped. This will help to balance the water pressure, act as a cushion against water hammer, provide a clean-out port, guard against pipe erosion and provide proper water flow to all air handlers. See sample piping schematic on pages 15 & 16 of this manual.

The chilled water circulation circuit shall not be connected to the potable water system.


The return side circulation circuit pressure gauge should read approximately 12psig when the system is running in cool mode and up to 20psig in heat mode. See "Fresh Water Fill System".

[11x17 DWG # H0050001]

[11x17 DWG # H0050001]


The chiller requires a properly sized chilled water pump for operation. Centrifugal pumps are recommended due to their quiet operation and longevity with minimal maintenance. The chilled water pumps are sized according to the BTU capacity of the chilled water unit. Service (ball) valves should be placed close to the inlet and the outlet of the chilled water pump for aid in servicing and flushing chilled water loop. A strainer should be placed between the inlet of the pump and the ball valve to catch any particles in the circulation circuit.


Marine Air Systems strongly recommends the use of 3/4" ball valves at each air handler to assist in start-up and overall serviceability of the system. The hose barbs supplied by MAS are for 5/8" marine grade hose (hose has 1/2" I.D.). Flexible reinforced hose is recommended for vibration isolation between the water circuit valves and the air handler. Couple the 5/8" hose from the air handler to the 3/4" ball valve and run 3/4" pipe or hose (1" for air handlers over 24,000 BTU) from the ball valve to the chilled water lines. Each hose connection should use double/reversed stainless steel hose clamps. See the diagram below.


The fresh water fill system must be installed on the return side of the circulation circuit and can be teed into the main return line at any convenient location. The system consists of a water pressure regulating valve assembly (with ball valve, check valve and hose bib, model HWRV), an expansion tank (model HXTK) and a pressure gauge. The system is installed with the pressure gauge closest to the main return line, then the expansion tank and then the water pressure regulating valve with the hose bib at the end (see the diagram on pages 15 & 16 of this manual). All three components are single direction position sensitive. Check each component's markings (inlet, outlet, water flow direction) before assembling system.

The water regulating valve (ball valve) is opened during filling and/or purging of the circulation circuit, and is closed while the system is in normal operation. While filling the system, this valve reduces the incoming water pressure to approximately 12psig (factory set), which is the static pressure for the chilled water system. The expansion tank allows the water in the system to expand as it gets hot when the chiller is in heat mode. The expansion tank also acts as a cushion against "water hammer". The expansion tank must be securely mounted to prevent vibration, and can be mounted in a horizontal or vertical position. The return side circulation circuit pressure gauge should read approximately 12psig on the return side of the system when running in cool mode and up to 20psig in heat mode.


Proper insulation of the chilled water circuit is necessary to insure maximum performance as well as protect against excessive condensation and possible water damage to the vessel. Use a closed cell type insulation rated down to 40F. Follow these instructions for installing insulation:

1. For pipes less than 1" in diameter, use " thick tube insulation. For pipes equal to or greater than 1" in diameter, use 1" thick tube insulation. Slide the tube insulation on each section of pipe prior to making the connections.

2. After making the connections, push the tube insulation flush against the fitting. Trim if necessary to ensure a smooth application with no air pockets.

3. Pipe insulation should be glued and not tie wrapped. Tie wrapping will compress the insulation and cause poor performance. There must be no air pockets between the pipe and the insulation. All joints must be glued. All insulation must be air tight.

4. If the tube insulation is installed after the circulation piping circuit is connected, proceed as follows:

5. When insulating fittings, follow the manufacturer's recommendation for the application of tube insulation. If insulation tape is used, follow the manufacturer's specifications to achieve equivalent R-value to the insulation of adjacent pipes. Overlap insulation with tape to insure that no ambient air is in contact with pipes or fittings. All insulation must be air tight.


The entire circulation circuit piping must be securely fastened in the vessel. The following recommendations should be followed:

1. Secure the insulated piping into the vessel using:


2. Compressing the tube insulation will cause condensation through the surface, resulting in saturation of the insulation and possible water damage to the interior of the vessel.

3. Any insulated pipe passing through a bulkhead should be supported with a piece of rigid material of sufficient length to distribute the weight evenly over a large surface. This will prevent excessive compression of the insulation.


METAL TO PVC FITTINGS: If connections are made between PVC fittings and metal fittings, always use a male pipe thread on the PVC fitting and a female pipe thread on the metal fitting. Reversing the type of fittings can cause the PVC to crack if over-tightened.

90 ELBOWS: All PVC piping should be installed with as few 90 elbow fittings as possible. Excessive bends can cause pressure drop in the system, affecting performance. Every 90 elbow is equivalent to adding 2 feet of additional pipe.


The following are suggested for better maintenance and operation of a chilled water system.

Sight Glass: Installed in the supply or return main pipes of the circulation circuit at an accessible location, the sight glass will provide visual inspection of the water flow for proper volume or air pockets.

Strainer: Installed in the return line to the circulation pump to catch debris and particles from installation of the piping (see diagram on page 15 & 16 of this manual). The strainer basket should be made of a fine mesh material to contain small particles. A clear base strainer could act as a sight glass also.

Ball Valves: Installed at the inlet and outlet of the circulation circuit pump are used to isolate the pump and access the circuit for maintenance, etc. If using a strainer as mentioned above, install the strainer between the ball valve and the pump inlet.

Water Pressure Gauges: Two gauges installed in the circulation circuit, one in the supply side and one in the return side, to monitor continuously for pressure drops in the system (the supply side gauge is optional, the return side gauge is mandatory).


After the chilled water system has been completely installed, the circulation circuit should be flushed to remove any contaminants or particles in the piping. Follow these instructions for flushing the circulation circuit:

1. Shut off the service valves to the air handlers.

2. Remove the flexible hose connection from the inlet hose barb on each air handler.

3. Remove the flexible hose connection from the outlet hose barb on the chilled water circuit.

4. Attach these two hoses using a hose barb. Do this at each air handler.

NOTE: The circuit may be flushed prior to attaching air handlers by following steps 4-9.

5. Install a strainer in-line to the suction side of the circulation pump to catch any particles. The strainer can be permanently installed in the system at this point to provide continuous trapping of any loose contaminants as well as provide a means to visually inspect water flow to determine air entrapment, glycol concentrations, etc.

6. Fill the system circulation circuit with water and run the circulation pump for fifteen minutes.

7. Turn off the circulation pump and close the service valves to the pump.

8. Remove and clean the strainer basket.

9. This procedure (steps 6-8) should be repeated until no particles or contaminants are visible in the strainer basket.

10. Upon completion of the above, drain the circulation circuit and reconnect the air handlers.


Pre-mix a glycol and fresh water solution per manufacturers specifications for your application. Use enough glycol to prevent freezing of pipes when vessel is not in use, but do not use more glycol than recommended. Mix the solution in a large container and either use a submersible pump (MAS P-500) or use the circulation circuit pump, priming the pump first, to introduce the solution into the circuit piping.

1. Connect hose from submersible pump to bib on water regulating valve and open the ball valve. Or, if using circulation pump, disconnect pump inlet hose from closed ball valve and place hose in solution after priming pump.

2. Turn the air handler circuit breakers 'ON'

3. Set all the air handler controllers to open their motorized water valves (refer to air handler control manual). Water valves may be opened manually if no power is available. Access the lever on top of the valve by removing the rubber boot.

4. Locate the bleeder ports on the air handlers on the highest deck.

5. Loosen the bleeder port on each air handler to allow air and water to drain into the air handlers condensate pan.

6. Start pump.

7. When no more air is coming out of bleeder and a continuous stream of water is visible, retighten the cap on the bleeder port.

8. Check the condensate pan for proper drainage.

9. Repeat steps 5-8 on every remaining air handler, as well as the bleeder port on the chiller, working down from the top deck.

10. Leak check all fittings and connections at this time. If a leak is found, close the fresh water fill valve and repair the leak. Repeat steps 1-9.

11. Steps 4-8 may need to be repeated until all air is removed from the circulation circuit.

12. Turn the air handler circuit breakers 'OFF'.

13. Turn pump off (and reconnect hose). Close the fresh water fill valve.

14. The pressure gauge should read approximately 12psig. Use the water regulating valve to adjust system pressure. See "Fresh Water Fill System".

For the purpose of protecting the environment, collect and discard discharged glycol solution in accordance with federal, state or local regulations.

Generic Wiring Diagram for Line Voltage MCW System


Set points for the thermostats are set at the factory and should not be changed. The set points are:
Mode Set Point for Stages 1,2,3,4,5 (F) Temp Sensing Probe Location
Cool 48, 50, 52, 54, 56 (differential 5-7) Chilled Water Inlet (Return)
Heat On @ 90 and Off @ 120 Chilled Water Outlet (Supply)

When the chiller is turned on, the circulation (chilled) water temperature will decrease or increase depending whether the chiller is in cool or heat mode. In cool mode, the compressors will stage on and off sequentially as the water temperature reaches the set points for each stage. In heat mode, the compressors will be staged on at 30 second intervals as regulated by their timers and the compressors will be turned off by their high limit switches as the water temperature reaches the 120F set point.


The control circuit for each stage of the chiller is connected to a timer. The timers are set at 30 second intervals at the factory. When the chiller is turned on, the first stage compressor will start in 30 seconds, the second stage compressor will start in 60 seconds, the third in 90, the fourth in 120, and the fifth in 150. If it is necessary to adjust the timers, set the dip switches to add up to the number of seconds desired for each compressor to start after the chiller is turned on. Do not set the time intervals for less than 15 seconds from one compressor to the next. Timer mode of operation is "delay on make".


High and low temperature control of the chilled water loop is protected by the high limit switch and freeze stat. The high limit switch has a 120F fixed set point and a 30 differential. The freeze stat is factory set at 38F and has a 6F differential.


A periodic check to confirm proper actuation/deactuation of the flow switches is recommended. While the chiller is running, turn off the chilled water pump. The chiller should shut down within seconds.


The following procedure should be followed when starting the chilled water system. With the installation complete and the circulation circuit filled and purged of air:

1. Open the sea cock valve to the sea water system.

2. Open all manifold valves.

3. Turn on all the system circuit breakers; chiller, pumps and air handlers.

4. Open all service ball valves to air handlers.

5. Open all the air handler water valves by adjusting their respective controllers. (Refer to air handler control manual.)

6. Turn the chiller on (COOL or HEAT) at the HRC control panel.


Chilled water systems require basic minimal maintenance to insure proper operation and long term reliability. Routine maintenance should be performed at frequent intervals. These intervals - daily, weekly, monthly - will vary from vessel to vessel due to its location and usage. Extended maintenance should be performed at semi-annual or annual intervals. Again, this will vary. Winterization of a system may be required for vessels stored or operating in extremely cold climates. As these items are performed over time, each vessel will develop its own "Maintenance Schedule"


The sea water strainers and thru-hull fittings must be inspected and cleaned regularly to provide sufficient sea water flow through the chiller's condenser coil. Obstructed sea water flow will cause compressors to operate at higher pressures, temperatures and amperages causing excessive wear on internal compressor components and possible nuisance tripping on the pressure switches.



  • Any silt, sand or marine debris should be removed from the strainer housing.

The chilled water circulation circuit must be filled completely with water. Air in the circuit will inhibit performance and cause possible nuisance tripping of the flow switches. Return water pressure should be approximately 12psig while in cool mode and when the system is off. Return water pressure may get as high as 20psig in heat mode due to water expansion. Discharge water pressure should be 25-30 psig while the system is running. Systems without gauges must rely on lack of cooling or heating from the air handlers, or audible noise in the pipes to determine that air exists in the circuit. Note: Continual recurrence of air in the system, or pressure loss, is a sign of a water leak in the circuit.

Return air filters for each air handler must be inspected and cleaned regularly to provide sufficient air flow through each unit. Obstructed air flow will cause poor performance of an air handler, resulting in reduced cooling or heating capacity.

  • Many filters are located on the back of the return air grille(s) or openings(s). Access the filter through the existing cabinetry or by removing part, or all, of the grille. Remove the filter and vacuum or wash it to remove particles, lint, etc. Do not use soaps or solvents when washing.

Electrical connections should be inspected and tightened as needed. Heat and vibration can cause connectors to loosen, causing poor contact and voltage drop or arcing. This can cause components to operate poorly, nuisance trip, or prematurely fail. To service electrical components:

  • Disconnect main power supply before repairing or replacing components or wires.
  • Tighten all loose connections at terminal strip and components (contactors, timers, relays, etc.).


  • Inspect connectors for burn marks, frayed wires, etc. If any are found, the connector or connection should be repaired/replaced.


  • Voltage to the equipment should be checked with a meter periodically to insure a proper power supply. Compressors, pumps, fans, etc. are electrically rated with a 10% value for voltage.

It is recommended that systems be operated regularly. Vessels not in use should have their chillers and air handlers cycled on 30-60 minutes once a month. Vessels in use should cycle on limited-use components in similar intervals to those above. Systems should also be cycled to their reverse mode (cool to heat, heat to cool). This helps to maintain pump seals and internal mechanical contacts, while reducing the fouling effect of marine growth in the seawater circuit.


Condenser coils and seawater hoses below the waterline can become fouled over a period of time due to marine growth and/or scale build-up inside the coils. This both obstructs water flow and prohibits proper heat transfer, causing continuous compressor operation with high pressures, temperatures and amperages.