Next Boat Outing: A Trip Through Marine Air Conditioning Maintenance and Repair

“Why is it so humid below deck? Is something wrong with the boat’s air conditioner?” asks the boat owner. Answer: Yes! It could be the marine air conditioner (AC) unit or the ventilation system, but humidity is a sign that something is not right.

The “wind in the hair” and the “cool breeze off the water” feels good and sounds poetic, but when the boat is moored or docked, things can heat up quickly in confined spaces like the boat cabin or sleeping areas if the AC is not working. In this discussion, we review the common problems boat owners experience with marine AC, suggestions for routine and professional marine air conditioner maintenance and repair, and a caution to the do-it-yourselfer.

Signs Things are About to Heat Up!

Air conditioners are one of the most enduring pieces of equipment on a boat, but that does not mean they never experience problems. Sometimes, the darn unit will not power on, almost always meaning there is an electrical problem. It could be a blown fuse, damaged wiring, a broken thermostat or a tripped circuit breaker.

Many times, the problem is less in-your-face. Following are some of the common indications a marine air conditioner is not happy.

Condensation pan overflows – The condensation pan collects humidity. This is sufficient warning that there is an obstruction in the pan nipple, the drain hose or the condenser filter.

Pump is noisy – Though pumps make some noise when supplying the water to the AC unit, too much noise is an indication of a problem. The reason for the noise could be the pump is no longer submerged or something has managed to get into the pump, like debris or marine critters. Other reasons for a noisy pump include lack of lubrication, worn bearings, damaged or missing fins or damaged components.

Evaporator freezes – Like any air conditioner, it can freeze up. This can be due to insufficient ventilation, blocked ventilation, an obstruction in the return air, a damaged fan or a refrigerant leak.

Circuit breaker keeps breaking – A circuit breaker that is frequently triggered could mean the circuit breaker itself is broken. Other possibilities include damaged wires or worn cables. It could also be due to equipment problems, like the compressor is short circuiting.

No water is discharging – If water is not discharging, it could be the strainer is clogged, sea cock is closed or a water strainer or pump is not underwater. When a strainer or pump is located in a place where a rocking boat leaves the strainer or pump high and dry, water won’t discharge.

No water is being drawn – If the pump is unable to draw water, it’s very possible the through-hull strainer is clogged. Though the strainer is intended to prevent debris or water creatures from entering your AC system, larger items pulled in can create a blockage. Another cause is a stuck valve. Fortunately, the AC will automatically shut off if unable to get adequate water flow.

Fan stops working – The air conditioner may work, but the fan does not. The fan capacitor or fan relay is probably faulty.

Not cooling like it should – If the AC is not cooling like it should, there could be several reasons. One is a refrigerant leak. Another is damaged insulation or solenoids not working properly. Of course, it could be someone went behind your back and turned the thermostat up!

Air conditioner blows warm air – Clogged air conditioning condenser coils can lead to warm air blowing, and usually when you most need cold air blowing. The coils will have to be flushed.

Thermostat is not working correctly – Thermostats are taken for granted. We assume they will work since it is such a small basic piece of equipment. However, a thermostat can break just like other equipment, or it’s not calibrated for some reason.

Humidity buildup inside the cooled areas - How annoying is humidity buildup? It is the perfect forum for mold growth and buildup. Some humidity is expected for the obvious reason the boat is surrounded by and on water. However, excessive humidity means the ventilation system isn’t able to keep up. If the return-air grill filter is dirty, airflow is restricted. As mentioned earlier, you should also check the condensate pan under the evaporator because that is where the humidity goes when it is removed. If everything looks good, a common suggestion is to add a dehumidifier to the area.

AC runs a little while and quits – Most AC systems have a safety switch to shut off the compressor when water flow is low. If the water supply is low, the raw water strainer may be plugged.

Keep Your Cool

There’s not a lot of maintenance required to keep your AC in good working order. Marine air conditioners can last for up to 20 years, and some are even older.

  • Inspect the evaporator coils for debris or frost build-up
  • Get in the habit of periodically working the through-hull valve so it does not stick due to lack of use
  • Again, regularly check the condensate pan for water accumulation which can indicate a clogged drain
  • Clean air filters monthly to ensure the evaporator works efficiently
  • Clean the water strainer basket once a month
  • Routinely inspect hoses
  • Look for worn or corroded clamps or any type of corrosion on metal
  • Check for condensation on the piping between the air handler and the compressor because this is where the cold refrigerant turned into low-pressure gas travels. If there is no condensation, the refrigerant probably needs charging.
  • Learn to read the digital codes like HPF (high pressure fault)

An HPF error code indicates the air conditioner has identified a high-pressure problem, so the high-pressure switch in cooling mode has been tripped. The system automatically shuts down to prevent damage to the AC unit. This is the unit letting you know there is not enough water to keep the system cooled.

Servicing the AC

The American Boat and Yacht Council (ABYC) is a non-profit organization that develops voluntary global safety standards for recreational boats. This organization considers the marine AC system important enough to offer ABYC certification in air conditioning and refrigeration. The certified technician is trained in installing, troubleshooting, and repairing the different types of systems.

Some things only a trained professional should handle, if you want to make sure your boat does not sink or catch on fire due to amateur installation or repair. Following is an example of just some of the repairs for which you need to find a marine air conditioning repair professional.

  • Replace a damaged compressor
  • Replace damaged wires
  • Replace a fan capacitor or fan relay
  • Inspect the through-hull fittings when the boat is out of the water to ensure it does not need replacing.
  • Calibrate thermostats
  • Clean the condenser coils to remove marine scum buildup every 2-5 years by flushing the system with pressurized water or a weak acid solution

Winterizing the AC system should also be left to a professional because he or she can winterize and check for signs of problems at the same time. Winterizing is important because water will remain in the heat exchanger when the AC system is not operating. The water can freeze in cold weather so must be removed. The marine mechanic will take steps like the following:

  • Force water out of the system
  • Run an approved antifreeze solution through the AC system and out a discharge port, using environmentally safe procedures
  • Clean the pump impeller
  • Check for signs of corrosion
  • Check for loose wiring
  • Clean the raw water filters
  • Do a general boat inspection

Many boat owners have worn antifreeze while trying to get it to run through the AC system. Most air conditioning pumps are not self-priming, meaning additional steps must be taken to get the antifreeze to go where you want it to go instead of all over your shirt.

And not to point fingers, but how many critical screws and ceramic washers lay on a lake or sea bottom after being removed from the pump head so it could be cleaned?

DIY Installation or Replacement of AC

Some boat owners decide to add air conditioning as a do-it-yourself (DIY), and selecting the right size of unit is critical. It’s not just a matter of saying, “That one!” or “DX.” An air conditioner that’s too big is going to continuously draw power. A unit that’s too small will not cool the area properly.

There are many considerations, including the size of the boat, the location (temperate or tropical climate), the load factor, the number of windows, the number of compartments to cool, the location of the compartments (to determine heat exposure in the sun and levels to be cooled), the ducting configuration, the amount of insulation in the boat, and…well…you get the idea. A marine air conditioning professional should assist with determining the right size and type of air conditioner.

A marine AC technician should also do the installation of the AC unit. DIY instructions say things like, “air access should not be contaminated by any other air from places like the bilge and engine room” and “secure the unit to accommodate its weight” and “properly ground all equipment” and “always use refrigeration grade, soft copper tubing.” Some instructions online try to make DIY AC installation seem easy, but beware of false promises.

No matter what, only a qualified technician should do the wiring. The wrong wire size can lead to a voltage drop that can damage equipment. Worse, the wrong wiring can cause a fire, and there goes your boat up in flames. Yes, it has happened more times than insurance companies care to mention. By the way, DIY installations also put your insurance coverage at risk should your boat get damaged by something you did.

There are always certain tasks an expert technician should handle. Electrical issues, water flow issues when clearing the strainer doesn’t work, and winterizing are just three. Raw water plumbing that leaks into a boat can sink it, and yes that has happened too. The AC system has sunk many boats due to faulty sea strainers and air conditioning fittings. It sounds implausible, but it’s true.

Wishing You a Cool Bon Voyage

Benjamin Franklin created the axiom, “an ounce of prevention is worth a pound of cure.” It is said today mostly in reference to health issues. Interestingly, he actually said it when addressing fire safety. "In the first Place, as an Ounce of Prevention is worth a Pound of Cure, I would advise 'em to take care how they suffer living Coals in a full Shovel, to be carried out of one Room into another, or up or down Stairs, unless in a Warmingpan shut; for Scraps of Fire may fall into Chinks and make no Appearance until Midnight; when your Stairs being in Flames, you may be forced, (as I once was) to leap out of your Windows, and hazard your Necks to avoid being oven-roasted."

A well-maintained marine air conditioner is not likely to force you to leap out of your boat and hazard your neck to avoid taking an unwanted swim. Marine air conditioning systems are really not that complicated, but don’t take it for granted. Sweltering while on your boat in the middle of summer is really no fun.

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