Article by Capt. Steve Katz
How to be Cool
The recent above average heat and humidity reminds us how nice it is to have air conditioning on the boat. Most mid and large size boats have multiple marine air conditioners to keep us cool while on-board.
Many smaller boats are also equipped with air conditioning, some are even DC powered compact units allowing them to run from the boat's battery system without the need for a generator.
During the hottest days of the season, keeping your marine air conditioner running at its best requires constant maintenance. There are a few common areas that need constant maintenance during the summer season.
A marine air conditioning system is similar to your home's air conditioning; the marine systems removes heat from the interior space using refrigerant moving through the system just like your home. At your home, the refrigerant is circulated to the outdoor unit and cooled with a fan. On a warm day, you can feel hot air blowing out of the outdoor condenser, that’s the heat that was in your house.
On your boat, the system works in a similar fashion except that the heat removed from the cabin is transferred to the seawater, through the use refrigerant and a water cooled condenser. This seawater cooling circuit is a common source of trouble for a marine air conditioner system. The most common issue is a clogged sea strainer that restricts the volume of water flowing through the system. A typical system requires 3 GPM per ton of air conditioning capacity (1 Ton = 12,000 BTUs) or about 200 gallons an hour/ton. If debris or marine growth clogs or restricts water flow to your air conditioning system, the unit will not work properly and may have reduced cooling or shut down automatically due to high refrigerant pressure. If this happens, it is best to clean the system as soon as possible, you may only have a clog in the seawater strainer or you may have a buildup of scale in the entire seawater plumbing lines –requiring an extensive cleaning.
At the opposite end of the system, the evaporator (usually located close to where the discharge air vents are located) can be a trouble spot too. Similar to the seawater side of the system but this time we need good air flow across the evaporator, to allow the refrigerant to remove the heat from the cabin. If there is a restriction in air flow, the refrigerant can freeze the coils, adding to the airflow restriction and this too can cause the system to automatically shut off due to high refrigerant pressure. A frozen coil will appear to look like a block of ice instead of many rows of shiny metal fins and tubing that make up the evaporator coil.
Just like your home, there should be an air filter that needs to be regularly cleaned or replaced at or near the air conditioner evaporator in the cabin. This is not always in a logical location and often there is more than one filter. It is necessary to find and clean this air filter on a regular basis for best performance. On the discharge side of the evaporator there is often flexible ductwork used to direct the cool air into your cabin. Often these hoses and discharge vents are located in areas that are also used to store gear and supplies and boaters can inadvertently block this ductwork, causing decreased air conditioning performance or frozen coils. If you have completed the preventative maintenance work and are wondering how to tell if the marine air-condition system is working properly – there is an easy test. Set the fan speed on the maximum level, let the system run for a while (15-30 minutes) then use a thermometer (digital is best) to measure the temperature of the warm air (return air) going into the evaporator (near where the blower is located) and measure the temperature of the cool air coming out (supply) of the evaporator. Most marine air conditioners should be able to cool the air about 12-20 degrees. If the temperature differential is lower than 12 degrees, you should have your system checked out by a professional, there could be a loss of refrigerant or other technical issue causing the system to not function properly.
As many of you know, the EPA (Environmental Protection Agency) has many laws that affect the refrigerants used in air-conditioning systems. There seems to be an endless variety of new refrigerants and brand names used in today’s modern units on boats and on land too.
Most of the newest refrigerants are a blend, made up of many individual gasses, each with its own physical properties. If you have a loss of refrigerant from a system with one of these modern gases, the system should be properly evacuated to remove all refrigerant and after repairs are made, the system should be re-charged to factory specifications. The reason the modern refrigerants need special attention is that a refrigerant leak can cause one of the many components the gas to leak out disproportionately from the other compounds in the mixture, therefore topping off a system with modern refrigerants will result in an improper ratio of the gases in the refrigerant often causing unexpected decreased performance.
Checking your system regularly, ensuring good water and air flow will save you money in service and also prolong the life of the marine air conditioner system.
