Beat the Heat with Proper Air Conditioning Maintenance!


Summer in the Houston area mean afternoon temps pushing 100 degrees with little cooling off at night.. Don’t let these temps keep you from enjoying getaway time aboard your boat!
A simple, avoidable air conditioning malfunction can make your vessel literally uninhabitable this time of year, and can easily ruin a weekend of much needed boat relaxation time. Exercising some good preventive maintenance can minimize the chances you’ll be hunting a hotel room or driving back across town because your A/C system let you down!

The following is a list of important Preventive Maintenance Tips that are generic to most Marine Air Conditioning Systems…


1. Let it Breathe!

Many people often overlook the simple task of cleaning the return air filter. This can be for good reason… Many times this filter is tucked away on the unit and hidden under a settee or inside a cabinet. Ease of access for regular removal and cleaning may not have been a priority for the builder or installer. Nonetheless, it is absolutely imperative this filter be cleaned regularly. Monthly is suitable for most, but if you regularly have pets aboard that shed, this frequency may need to be increased. Not only will a clogged or dirty air filter restrict air flow and affect the performance of the system, it can also cause the filter to trap and hold condensate water which can freeze. This can restrict air flow and speed corrosion of adjacent aluminum evaporator fins, leading to expensive repairs, or even replacement.

Here are some other air filter points to remember:

  • There may be two air filters in your system –One at a return air grill installed in the cabinetry that allows air into the compartment the unit is installed in, and one just in front of the evaporator actually on the unit itself (even though most manufacturers specify only one be installed…). Sometimes the locations of these filters may not always be obvious. One of our HVAC technicians would be happy to look over your installation and identify where yours are located.
  • Do not use air filters designed for residential AC systems –Filters from Home Depot, Lowe’s, or other hardware stores are usually too restrictive for the available surface area of marine return air grills. Don’t be tempted to install these thinking they will do a better job of filtering the air. They will likely cause other problems and actually diminish the performance of the unit.
  • Proper return air filters are washable, or can be vacuumed – Most filters installed at the unit’s evaporator are made of a nylon mesh and are intended to be washed with soapy water or vacuumed. Some filters installed at return air grills are made of expanded aluminum and are similar to the filter you would find in a range over a residential stove. These too can be washed, but are sometimes more difficult to clean. Again, our technicians would be happy to clarify cleaning instructions specific to your filters.

2. Keep the Sea Water Flowing!

Sufficient sea water to cool the condensing coils on your unit is an absolute requirement, especially as sea water temps in the marina are on the rise. No doubt you’ve encountered the notorious high head pressure fault codes if you have a digital controller (“HI PS”, “HHH”, “HPF”etc.). This typically means the unit lost sea water flow, or the flow dropped below the minimum level required.

The following steps can be taken to help avoid this aggravating shut-down:

  • Keep the strainer basket and bowl clean. If you leave the system running for humidity control to protect the boat’s interior when you are off the boat, cleaning of the strainer and basket will be required more frequently. Depending on your system, this may be required on a monthly basis, or as often as every few weeks. If you leave the system off when not on board, the sea water in the system will become stagnant and there will not be continued marine growth, but your interior may suffer. Pick your poison…
  • Perform periodic dock water flushes. Our local water can be heavily laden with silt and other debris. In addition, in the summer months with higher water temps marine growth can occur inside the entire sea water system, from the intake thru-hull to the overboard discharge (usually most accelerated at the sea water strainer). Once this growth takes hold, it quickly traps and holds silt in the passing sea water. The results are eventually the familiar high head pressure shut-down. Periodically disconnecting the plumbing at a convenient point and flushing the system with dock water will clear the majority of growth and silt from the system and restore proper flow rates. If it progresses past the point where dock water flushing corrects the problem, more aggressive chemical de-scalers or hose replacements may be required.
  • Know your boat! Keep an eye on the AC sea water overboard discharges. Make a mental note of the distance the water shoots out beyond the discharge thru-hull when the system is operating properly. If you notice this distance start to decrease, you’re probably headed for trouble. Eventually you will acquire a feel for when the system requires maintenance. You can also feel the temperature of the discharge water. If it is noticeably warmer than the sea water it is discharging into, the system is pushing the limits of its cooling capacity.

3. Check the Temperature Drop

If your system is working correctly, it should be dropping the temperature of the air going through the evaporator approximately 17 to 20 degrees. This can be measured easily using a hand-held infrared temp gun, or any traditional thermometer. After the system has been running for at least 15-20 minutes, measure the temperature of the fins of the return air grill, as well as a supply air grill close to the unit. If the difference is 15 degrees or less, it’s likely the system has some sort of problem (possibly low on refrigerant). There are some installations where this can be difficult to measure, or measurements can be misleading, so again, ask a professional for advice, if needed.

4. Keep an Eye on the Condensate Pan

An overflowing condensate pan that goes undetected can cause a multitude of problems. Rotted wood, mildew, rust and corrosion of other components, etc. Check the condensate drip pan at the bottom of the unit below the evaporator each time you clean the air filter. Be sure the level of water is not higher than the drain connections at the sides of the pan. If they are, this indicates a problem with the drainage system. Abnormally high water levels in this pan can cause accelerated rust and corrosion on critical components like the evaporator and compressor that the high level of condensate water can contact. Algae, collapsed or kinked hoses, poorly installed drain hoses, and malfunctioning pumps intended to handle the condensate water are just some of the potential culprits. Remember: don’t underestimate the value of a regular inspection! Many times units are installed in tucked away places and a small problem can become exponentially more expensive if it’s allowed to go unnoticed for long periods of time.

5. Inspect Your Shore Power Cables

Always, always, always… insure your shore power cables are securely connected to both the vessel and the dock power pedestal. All retaining rings and couplers should be in place and tightened securely. If you are using Y or other step-down adapters, make sure the couplers and locking rings are installed and tight. If these components are not in place and properly utilized, movement at these joints (as the boat rocks in the slip) can happen under heavy current loads and can cause arcing that damages terminal platings. This eventually leads to corrosion, high resistance connections, and overheating. Best case – a plug end melts and leaves you without shore power. Worst case – the overheat causes a fire, open flames, and an incredibly dangerous situation. 80% of the shore power cable problems we encounter happen during the summer months. This is because of the high current demands of the on board air conditioning systems operating at max capacity. Few other systems require as much current as they do. You may have noticed new Marinco EEL shore power cords have spring loaded clamps instead of locking rings. The jury is still out on how well these work…

The maintenance points detailed above are intended to provide a basic overview of the major maintenance items that will keep your system performing reliably, even during these tough summer months. If you would like your system checked and serviced by our trained technicians, please contact our office today.

True North Marine offers a Preventative Maintenance Service for Air Conditioning Units:

  • Initial measurement of temperature differential between return and supply air (17-20 degrees F optimal)
  • Clean return air filter(s)
  • Clean evaporator, if necessary
  • Inspect condensate system for proper operation
  • Clean sea water strainer housing and basket
  • Flush hoses downstream of AC sea water pump
  • Back flush strainer and thru-hull (as possible)
  • Exercise unit in heat/cooling mode (opposite ambient temperatures)
  • Connect gauges to unit and charge with refrigerant (if necessary)
  • A cursory leak check if refrigerant levels are low (smaller leaks may require additional, more aggressive leak detection methods and are not included in the scope of this service)
  • Inspect AC unit ducting and audit installation. Make any recommendations to improve performance.
  • Measure before and after readings of temperature differential, sea water flow rates, and heat absorption across condenser to evaluate and track unit performance.

Note: Any needed refrigerant or other supplies are not included in the cost of the service and will be billed based on usage.

This service is designed to keep your unit running at its peak performance, as efficiently as possible. Poor maintenance (dirty air filters, clogged sea water plumbing, low refrigerant charge, etc.) can cause excessive wear and tear to an expensive piece of equipment. It can also cause higher electric bills because the unit has to run longer to achieve the same results. Investing in preventive maintenance will give you the best chance of getting the expected service life from your expensive equipment!


1 reply
  1. Eli Richardson says:

    It’s great that you elaborated on air conditioners and how preventive maintenance helps us keep them in good shape. Last month, my dad purchased a boat, and the last time I visited it, I noticed how his AC wasn’t cooling like before, so I believe my dad will benefit from reading your advice. Thanks for the information on cleaning our air conditioner’s air filters and evaporator to keep it working efficiently.


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