Guy doing an inspection of a tiny house on wheels

Boat Air Condition Problems: 14 Common Issues (+ Solutions)

In Boating by Morten Storgaard

Nothing beats a summer retreat on your boat. But an ailing marine air conditioning system can spoil the fun and force you to a nearby hotel.

Thankfully, you can troubleshoot your boat’s AC unit on the water so you don’t have to swelter in the heat while others are having a blast.

In this article, we look at the common issues to check when your vessel’s AC stutters.

At the end of this piece, you will know the basics to keep your air conditioner in top shape.

1. Read the User Manual (All Of It!)

Guy doing an inspection of a tiny house on wheels

Before troubleshooting your marine air conditioner or any other equipment, read and understand the user manual.

The manual explains the things you can check in the system and the correct procedure.

It also lists the activities which are not DIYable and so you can call professionals.

Depending on the brand and model of air conditioner, the following are things to check when you have issues with your boat AC.

2. The AC Does Not Power On

What happens if you turn on your AC but it doesn’t come online?

Causes and Solution

If you turn on your boat AC unit but can’t feel or hear anything, it could be from different factors but all of them are related to your electrical circuitry.

The problem might be from a loose or broken wiring.

It can also be a tripped circuit breaker or blown fuse which will need a replacement. Check that there are no loose or disconnected wires.

The thermostat might also act up so make sure it works properly.

Check that the AC pump is working as it provides cooling water to allow the unit operates without problems.

You can change a burned fuse or tripped circuit breaker, but don’t attempt retrofitting your marine AC unit’s electrical connections except you are qualified.

If you make mistakes with the polarity of live and neutral wires, you can end up frying the whole system and cause extensive damage to the unit and your boat.

If the above tips don’t help, call a professional or the manufacturer’s customer support.

3. Frozen Evaporator

Like your car’s radiator, the evaporator in your boat’s air conditioner can freeze during operation.

Causes and Solution

This problem is usually the result of insufficient ventilation.

Either the vents are insufficient or the existing ones are blocked. Clean the existing duct system or increase the vents for adequate airflow.

Check the minimum number of vents the system requires for optimal performance and upgrade as required.

It can also be because of obstruction of the return air. Remove any blockage and clean the air filter to improve ventilation. A freezing evaporator can be because the fan is not running efficiently or is damaged.

Check to see that the fan is running properly. A leak can also lead to a frozen evaporator as it reduces the level of coolant. For this, you need a professional to find and seal the leak and refill the Freon.

You can also experience this problem if the thermostat is set too low.

Increase the thermostat setting to remove ice from the system.

An improperly located thermostat may also have difficulty gauging the actual cabin temperature, leading to this problem. In that case, move the thermostat for correct operation.

4. Activation of High-Pressure Switch in HEAT Mode

This issue occurs when the high-pressure switch, i.e., RESET activates while the air conditioner is operating in HEAT mode.

When this occurs, the evaporator will not dissipate heat effectively.

Causes and Solution

The main cause of this issue is restricted airflow and can be corrected by removing the obstruction.

You may also trigger the HEAT sensor when operating the AC during warm temperatures.

Inspect the air filter and clean it for proper ventilation.

Check the return air. Remove anything restricting the air flow.

It can also be because of insufficient or blocked supply air grilles.

Increase the air grilles and remove any obstruction to the ventilation. The evaporator’s duct might be too lengthy or kinked in places, causing a heat build-up that triggers the RESET button.

5. No Heat in HEAT Mode

This problem arises when the air conditioner does not produce heat in HEAT mode.

Causes and Solution

This indicates malfunctioning reversing valves.

Turn off the power and check for loose electrical connections in the electrical box.

Inspect the reversing valve relay to see if it’s burned.

Check to see whether the reversing valve sticking produces a hissing noise when you tap it with a screwdriver during operation. The wire on the reversing valve solenoid might be loose or worn. Reordering the connection might solve the problem.

Contact a technician if none of the above works.

6. Overflowing Condensation Pan

An overflowing condensation pan can flood your boat if not corrected on time.

Causes and Solution

When your air conditioner’s condensation pan overflows, it means an obstruction.

The first step is to clean and clear the pan nipple of any debris that might restrict the flow of water.

Check the drain hose. It might be blocked, kinked or misaligned.

Clear the hose if it’s an obstruction. Reassemble in case of misalignment and replace if it has extensive kinks. The AC unit may not be elevated enough for the water to leave the pan nipple. Raise the elevation to restore flow.

Check the condenser filter.  A dirty condenser filter will restrict the flow of water, and this can cause the unit to overflow.

You can clean the filter but extensive clogging will need a replacement.

7. The Air Conditioner Does Not Release Water

Here, your boat’s AC unit works normally, but it’s not discharging any water.

Causes and Solution

The thermostat should be in off position. Inspect the raw water strainer and flush if dirty or clogged.

Make sure the sea cock is open and prime the pump to activate.

Check that the AC pump works properly and replace if faulty.

Make sure the condenser coil’s caps are removed and the water strainer and pump are below water level.

If everything fails, flush the unit with a pressure hose or call a professional if you can’t identify the source of the problem.

8. Circuit Breaker Triggers Uncontrollably

If your AC unit’s circuit breaker will not stay on, it may be because of:

Causes and Solution

Check that the circuit breaker is not broken.

Replace a faulty circuit breaker.

The problem might be from a shorted wire.

Check for disconnections and reconnect or replace any loose or worn cables. An internally short pump can also cause the problem. To check this, disconnect the pump power and start the AC.

Replace the pump if it doesn’t trip off the circuit.

It can also be because of a short circuit in the compressor and this requires a replacement by a professional.

9. Fan Does Not Work While the Compressor Is Running

This occurs when you are using the thermostat. The compressor works but the fan doesn’t.

Causes and Solutions

Test the fan with a jumper to determine if it’s still working. To jump the fan, isolate the RED and GREEN wires in the thermostat connection. But this may prove difficult based on the model and your experience.

Sometimes the problem is from a faulty fan relay or capacitor.

These problems usually require replacing the faulty component.

Turn off all the power from the boat before attempting to troubleshoot electrical components.

And when in doubt, always call the professionals.

10. Activation of High-Pressure Switch in Cool Mode

This problem occurs when the high-pressure switch is triggered while the AC unit is operating in Cool mode.

Causes and Solution

Whenever you experience this problem, check that water is flowing through the AC unit.

Kinks in the hose, debris, and clogged lines to the seawater pump can restrict the flow of water.

Flush the unit with a pressure pump if it is blocked. Replace or service the seawater pump if it is failing and change kinked hoses.

11. Reduced Cooling Capacity

You may notice that your boat’s AC is not as cool as it used to be despite the compressor and fan working normally.

Causes and Solution

If your marine AC is not cooling like before, maybe the refrigerant is leaking.

Locate the leak and refill the coolant.

Poor or damaged insulation can reduce cooling. Malfunctioning solenoids can compromise the AC’s function.

If the thermostat is poorly positioned, it may sense cold temperature and reduce the unit’s cooling effect. The proper position of the thermostat is the evaporator discharge.

A hatch or window might be open. Check your boat for any spaces that can allow warm air into the cabin.

Clogged air conditioning condenser coils can make your boat unbearably hot. If this is the problem, flush the system for improved airflow.

12. Clogged Thru-Hull

The thru-hull allows your boat’s AC unit to draw raw water from the sea. If it’s clogged, it can reduce cooling and even damage the system.

Causes and Solution

The thru-hull lets water in and out of the AC unit.

But it is an ideal location for critters and debris to accumulate.

Over time, excessive amounts of materials in the sea strainer that acts as a barrier between the water and the thru-hull can cause a blockage.

The AC will shut off if it doesn’t get water flow to prevent overheating.

Make sure the thru-hull, sea strainer, and valves are working perfectly. Remove accumulated growth and move the valves frequently, especially if the boat will be out of the water for extended periods.

13. Loud Air Conditioner Pump

The AC pump in your boat is a vital component that must work perfectly to keep your vessel cool.

This pump provides the freshwater that cools the AC unit, preventing it from overheating.

But to perform optimally, the pump must always be in contact with the water.

If the pump makes a lot of noise, it has something in it.

Causes and Solution

A loud AC pump indicates debris or air.

The pump needs to be submerged to draw water into the AC unit.

If the boat planes or the waterline changes, it can leave the pump out of the water, preventing it from performing optimally.

The entry of large particles, critters and debris can also make the pump noisy. When this happens, turn off the pump and the AC unit to allow it to cool.

Check the pump for debris and clean up.

Sometimes, the noise is because of friction and some lubrication will stop it. Faulty bearings can also make the pump loud. If the AC pump is missing fins, has melted components, or worn bearings, replace it.

14.Noisy AC Fan

Your AC unit’s fan keeps the evaporator coil cool for efficient operation of the condenser. However, the fan may become noisy to the point of being uncomfortable.

Causes and Solutions

Often, a noisy AC unit results from a dirty fan motor.

If the fan has accumulated dirt and debris, has damaged bearings or worn belts, it will be loud.

Shut off your marine AC unit and troubleshoot the fan and adjoining areas.

Clean with a blower if you notice debris or dust buildup.

If you explore all options but the noise persists, call a professional.

Marine Air Conditioner Maintenance Tips

If you live in a place with humid summers and cruise on mosquito-infested waters, a working AC unit is a must.

But you won’t get the best service from your climate control system without adequate maintenance. Use these tips to keep your AC unit in excellent shape.

Check the Cooling Water Intake Strainer

The most important maintenance check for your marine AC unit is to ensure the water intake strainer is in excellent form.

Check for marine growth, large particles, sea scum, and debris.

Because the water flow passing through the strainer is nutrient-rich, critters and small marine life love to lodge in the space.

Inspect the thru-hull, strainer basket, and valves.

Look for damage, clog and anything which can obstruct the smooth flow of cooling water.

Have spare air conditioning strainers onboard as the constant flow reduces the longevity of the baskets.

Clean the Air Filters

The filters ensure your air conditioner exchanges heat efficiently.

Dirty and clogged filters make your AC unit inefficient, increasing the system’s workload. It makes the evaporator dusty and decreases its heat-dissipating abilities. Clean your air conditioner’s filters monthly by washing with plain water, vacuuming or blowing.

Allow them to dry thoroughly before reassembling as moist filters attract dust.

Check the Ducting

It’s vital to check all connections and hoses.

Inspect the hoses from the sea stock, strainer, pump, to the thru-hull.

Check for cracked and leaking hoses, broken, worn and corroded clamps, and replace old components.

A leaking hose is not only bad for your AC unit, but it can flood your boat and even sink it if you are running the system while the boat is empty.

Clean the Condenser Coil

The condenser coils can accumulate scale which restricts cooling water flow.

Marine growth can also clog condenser coils.

Manufacturers recommend flushing the condenser coils to remove marine scum and scale every two to five years based on the frequency of use or location.

You can flush the system with a weak solution of biodegradable acid or pressurized water.

Check the Condensate Pan

The condensate pan is the tray that collects the humidity the AC unit draws from your boat.

Make sure the pan is not corroded as this can lead to flooding and will need a repair or replacement.

It’s important that the water drains properly. We covered this at length in the troubleshooting section.

Clean the Evaporator Coils

An efficient air filter reduces the dirt and dust collecting on the evaporator coils but you need to clean it after some time.

Dusty evaporator coils are inefficient and will increase the strain on your unit. Check your user manual for the correct way to clean the system or ask a professional to perform detailed maintenance.

Call a Professional

Except you have a background in HVAC systems, there is a limit to what you can with a troublesome marine air conditioner.

After trying all the troubleshooting tricks in the book and you can’t resolve the issues with your cooling unit, ask for professional help.

A professional marine air conditioner technician has requisite experience and up-to-date tools to perform in-depth diagnostic tests, repairs, and maintenance to bring your unit up to speed.

This option might be costly than DIYing your maintenance, but it will save you time, efforts and help you enjoy more quality time on your boat.

Final Words

A boat’s AC is a vital system for an enjoyable boating experience during the summer.

But the unit can stop working without notice. This makes it imperative to know basic things to troubleshoot when your marine cooling system fails suddenly.

We hope this article will help keep things cool when it’s blazing hot on deck.