Cleaning Boat AC Seawater Lines

Sea Water Flow Issues in Boat Air Condition Systems

If your marine air conditioner isn't working properly, one of the most common problems is restricted flow of seawater through your ac unit. Before doing any sophisticated or more involved work on your boat's air conditioning system, remove and clean all the filters and do the same with your strainer (MAKE SURE YOU CLOSE YOUR SEA COCK FIRST).

Groco Strainer Cleaning
Probably not a lot of water flowing through this strainer...

Check out our Marine Air Conditioner Troubleshooting page for these and other recommendations on determining why your boat ac isn't working properly.

Once you get through those, if your thru-hull discharge still seems to be discharging less water than previously or isn't flowing smoothly, your marine heat pump or marine air condition system won't be able to pull heat from or dump heat into seawater quickly enough for optimal performance.

We see more water flow issues on boats that are moved less often, boats that are stored in well-protected marinas or harbors, boats that often travel in shallower, muddier water and boats with older marine ac systems. Most water flow issues stem from obstructions in the cooling water system - usually mud, algae and/or debris.

Here are some examples of error codes that can be caused by insufficient saltwater flow and/or high water pressure in your marine air conditioner.

Marinaire: error code E4 or error code E7

Webasto Marine: error code A01, error code A02, error code A15, error code A20, error code A23, error code A28

Mermaid Marine: error code P-6, error code P-9

Dometic Marine: Hi-PS, HPF (High Pressure Fault), Lo-Ps

Determining the Water Flow Rate in Marine AC

To check water flow, you can use "the bucket test"

small boat air conditioning
Our setup to clean boat ac water pump lines.

Thanks to Marinaire for providing the tables below for calculations. Low salt water pump flow is a common issue and will result in an E4 code on Marinaire units. In order to test whether your boat's ac pump is circulating enough water, you can use the following "bucket test":

  1. Turn on your circulation pump (i.e. March Pump) - may require turning on AC unit - and open your seacock
  2. Grab a 5 gallon bucket with a line attached to it. NOTE: most 5 gallon buckets are actually more than 5 gallons if filled to the rim. Generally they will have a ring inside the bucket that shows the true 5 gallon mark - usually about 2 inches from the top
  3. Grab a stopwatch that measures seconds (iPhone or Android timer, for example)
  4. Begin filling the 5 gallon bucket and start your stopwatch
  5. When the bucket is filled to the 5 gallon mark, stop the stopwatch. Note the time (in seconds) and refer to the table below to determine if your flow rate is sufficient. If you have multiple ac units using the same pump, add the GPH requirement for each and adjust time by the same % (i.e. twice the GPH means the bucket should fill in half the time)

6000 BTU

Must be filled within 120 sec

9000 BTU

Must be filled within 100 sec

11000 BTU

Must be filled within 75 sec

14000 BTU

Must be filled within 65 sec

16000 BTU

Must be filled within 55 sec

20000 BTU

Must be filled within 40 sec

24000 BTU

Must be filled within 35 sec

 

For current Marinaire models, these are the recommended minimum water flow rates

MSBA6K/C2

300 GPH

MSBA9K/C2

300 GPH

MSBA11K/C2

500 GPH

MSBA14K/C2

500 GPH

MSBA16K/C2

500 GPH

MSBA20C2

1000 GPH

MSBA24C2

1000 GPH

How to Clean Your Seawater Cooling System

We have built a special tool that we use to clean out seawater circulation systems for our customers. We use compressed air to push a column of water that essentially power washes seawater piping from the seacock to the through-hull inlet to the thru-hull overboard discharge.

In the video below, you can see how we do this. You'll be able to see how much dirt and debris comes out and how much the flow level improves afterwards.