Marine A/C Pumps & Pump Relays


In earlier articles we have touched on seawater cooling and lack of...Now what about if you have a intermittent problem, or the pump won't start at all ?

In boats with multiple systems running on one seawater pump there is most likely a Pump Relay to receive a signal from each system to tell the pump it needs to run...That is unless it has been bypassed and the pump runs 24/7 from the breaker ( I see this done fairly often)

Lets start with the breaker in the main panel...Most are labeled A/C pump or similar...Some boats may have the pump breaker tied in with one of the A/C system breakers (Ocean Yachts for one used to connect the pump to the Main Salon A/C Breaker) but most should have a stand alone breaker...

The breaker feeds the pump relay and carries the load of the pump only...this power can be either 115 or 230 volts depending on the pump installed...

The individual systems aboard will then have their own breaker that powers/protects each A/C system & it's wiring...These can also be 115 or 230v supplied...The reason I describe this is that some boats have a mixture of system voltages...Hatteras for example, always supplied one of the smaller systems as 115v and the rest as 230v...They would then install a 115v pump so that if all that is available on the dock is 115v, you can still have at least one cabin of A/C for crew/kids while the owners/parents go to the resort for the night without starting the generator (Well this has always been my assumption and nowadays most docks will have 230v anyway)

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There have been many types of pump relays over the years...Some with mechanical relays (in previous times) but most for many years have been "ignition protected" solid state designs...Here are the most current & popular versions that I see, and a few of the most common failures...

Some were for built for only 2 systems and could not be expanded for more...Marine Air still makes a 2 unit relay (2PRP) but they also offer one that can handle up to 6 systems (6PRP) on one pump...you don't have to utilise all if you have say 3 or 4 systems, and it actually gives you spare circuits to re-connect a system to if the one it's connected to were to fail (that is if you have the 6PRP)...These relays are just a metal box with a single circuit board and all needed components on that board...Other than complete board replacement, there are no repair parts available/needed.

Cruisair went about it a bit differently...Years ago they offered one pump relay that could handle up to 8 systems on one pump (PR8X) and it came with individualized components, all of which could be replaced...The "Circuit Board" & separate" Triac" (solid state relay that switches & carries the pump current) came with the box...You could then add "Triggers" for as many units as needed, and you could also select trigger voltage (115 or 230) to match the system voltage feeding it....These triggers of course were/are replaceable with two screws & two plug on wires in the event of failure...

The only problem with this Pump Relay was the box was a bit large for smaller areas in boats that may only need 2 or three triggers...So they built a smaller box that can house all the same basic components (circuit board & triac) but only has room for up to 3 triggers...It can also be purchased with the triggers pre-installed for either 2 or 3 systems (PR3X-?) The question mark would be the number of triggers pre-installed (either 2 or 3)...They still offer the PR8X, and it can also now be purchased with triggers pre-installed but either box is not hard to add/install trigger/s in...

The main purpose of these relays is to run the pump when a system is calling for it...That means any system that is running a compressor (Some with just fan, IE: older Three knob cabin control-ed systems)...But if a trigger circuit in either type box fails (Marine Air, Cruisair, or any manufacturer) the pump may run for one or more systems...But not for the one that has the failed trigger circuit...

This sometimes causes confusion because if any one of the good triggers starts the pump...All systems that are connected to that pump will get seawater, and thus run normally....

However if the system/s with the good trigger/s cycle off, and the one with the bad trigger either continues to run, or starts up with the others off...It may/should shut down randomly with a fault code on the cabin display.

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The easiest thing to do to verify if you have a problem is to test run each system" individually" to verify if you are pumping water with just that system running...If you find a system that won't start the pump, the trigger circuit (in the pump relay) for that system has likely failed.

Also if the pump won't run at all...These Pump Relays all have fuses installed either inside the box (Newer automotive type pull out fuse) or in a typical twist type fuse holder mounted thru the box ( It's how Ocean Yachts gets away with running the pump on the salon breaker)...This should be one of the first things to check....If the fuse is blown, and then blows again after replacement, it's time to look at the pump & associated wiring for shorts or bad/wet connections.

These Pumps & Relays are pretty easy to troubleshoot with a volt meter and a bit of common sense, but going into that here would be a bit long for all models...If you want help with your individual installation, I'll be more that happy to answer in the forum troubleshooting section  https://marine-ac.com/forum/troubleshooting/

Just let me know what you have and we can solve it there together...If you have another brand of equipment or model of pump relay, it's likely that I have seen a few...We can figure those out together too...

Steve~