Article by Capt. Steve Katz
Keeping Cool
The recent above average heat and humidity reminds us how nice it is to have air conditioning when we go indoors. Most mid and large size boats have multiple marine air conditioners to keep us cool while on-board. Many smaller boats are equipped with air conditioning that are DC powered compact units allowing them to run from the boats 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 and there are a few common areas that need attention during the summer season.
A marine air conditioning system is similar to your homes system. The marine systems removes heat from the conditioned 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 the 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 sent into the seawater through the use of a water cooled condenser. This seawater cooling circuit is a common source of trouble for a marine air conditioner. 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, since most pumps are rated in GPH. If debris or marine growth clogs or restricts water flow to your air conditioning system, the unit will not work properly and probably overheat or stop working due to the internal limits on 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 seawater plumbing lines that would require an extensive cleaning.
At the opposite end of the system, the evaporator can also be a trouble spot. Similar to the seawater side of the system, but this time we need good air flow across the condenser 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 often causing the system to turn off due to the internal limits on 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 is 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 duct work used to direct the cool air into the cabin. It seems like these hoses and discharge vents are located in areas where we like to store gear and supplies and the airflow is inadvertently blocked, causing decreased air conditioning performance or frozen coils.
If you have completed the preventative maintenance work and are wondering how to tell if your marine air-condition system is working properly, there is an easy test. Set the fan speed on the maximum level and let the system run for a while. 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 to 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 issues causing the system to not function properly.
Regarding refrigerants, as many of you know, the EPA (Environmental Protection Agency) has many laws that deal with the refrigerants used in air-conditioning units. There seems to be an endless variety of refrigerants and brand names used in today’s modern units, both on boats and on land. Most of the newer refrigerants are a blend, made up of many individual gases, each with it’s own physical properties. If you have a loss of refrigerant from a system with one of these modern gases, most likely the system will need to be vacuumed to evacuate all of the refrigerant and after repairs are made, new refrigerant needs to be added to the system. The reason for this is that a leak can cause one of the many components to leak out disproportionately from the other compounds in the mixture, so just adding new gas will result in an improper ratio of refrigerant, often causing an unexpected decrease in performance.
If you are wondering if you can convert your marine systems refrigerant from one of the limited supply expensive gases, like R-22, to a more environmentally friendly and less expensive refrigerant, it is possible but may not be effective in cost or performance. There are some “drop in” replacement refrigerants that can work if needed, so contact your local marine air-conditioning expert to review your options.
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.
Captain Steve Katz is the owner of Steve’s Marine Service and holds NMEA, AMEI and NMEA2000 certificates along with ABYC Master Technician certification and factory training from many manufacturers. To reach Steve, call (631) 264-1600.
