The Advantages, and Disadvantages of a Hold Over system are similar to a block of ice because that is essentially what is done…

The hold over plate/s in the box is/are approx 3″ thick, and have copper tubing run through them which is then surrounded by a liquid that freezes (and re-freezes) when the refrigeration system is run… a Block of Ice really…The idea is to not to have to run the system but once or twice a day to maintain a box’s design temp.

The the solution/liquid is generally a glycol solution (or brine water in older plates) that is mixed for a lower freezing point than water…A refrigerator plate solution can be mixed to around 26 degrees F…A freezer plate can be 0 degrees or even lower depending on the temp you want the box maintained, and how much insulation is surrounding the box (more on that later)

Other than what I have stated above…There really aren’t that many advantages to a hold over plate system…Yes they can work well for the intended purpose, and have for many years for that purpose…Thing is, they really are nothing like what most folks are used to at home, and that in itself  can be one big disadvantage…

If you have, or are considering a hold over system I will try to list some of the lower points when compared to a traditional refrigeration system…

• Expense…Custom Hold Over Systems & Boxes are expensive to design & build…Proper insulation & door gaskets are key factors too…Insulation should be around 4″ thick everywhere (even against the hull) with no air pockets.
• Given Space…The insulation requirements and the space the plates take up, really tend to limit internal box size in the space allocated for a box.
• Weight…A plate full of liquid is quite heavy.
• Power…Big plates full of liquid require a large refrigeration unit to pull them down to temp, and Initial pull down time is also much longer to get the box temp to stabilize.
• Recovery…Holding Plates don’t recover temp very fast after opening the box…No more leaving the door open at all…In fact you really should only open them once a day…But what about my beers ?
• Defrost…Any ice build up acts like a insulation blanket over the plate, and thus raises box temp…By design, hold over plates can’t utilize auto defrost cycles effectively, so you end up scraping the ice off all the time to maintain temp, and the more you open the door…The more the ice/frost forms…Break out that windshield scraper you came south to get away from. (but at least up there you could put the beer outside)
• Safety…Last but not least is the possibility of a Glycol leak into your food without knowing it…Yes it’s rare but does happen…Glycol is like antifreeze in your car and is Very toxic.

I have found one of the biggest misunderstandings about Holding Plate systems is…Hold Over Period Box Temp/s…I’ll try to explain…

Hold Over Period is the time it takes the plates to thaw from a solid back to a liquid…Hold Over Period Temp is the box temp during that period…This is where the box/system was designed/intended to operate….

Any additional run time below the freezing point of the solution is pretty much wasted energy because the plates will rise in temp very rapidly back up to the change over (thawing ) point anyway…Then the box temp will again rise rapidly when the solution has thawed (if the compressor is not run)

This is where insulation, door gaskets, drains etc… Have the most effect…Ideally with all things at their best, you would like to maintain a box temp that is 15 degrees above the plate temp when the plate is frozen…That means with a 26 degree refrigerator plate you might expect a 41 degree hold over period, and with a 0 degree freezer plate you might expect +15 degree hold over temp  (not good for ice cream)….Yes you can go lower with the solution temps (mixture to attain lower freezing point) but to effectively do that you will need to use a system that is set up for a lower temp refrigerant than the old standard R-12 or it’s replacement R134A systems that we have seen for years…Grunert offers a R-404A system and plates mixed to do it…

Different than a conventional system (non hold over) that senses ambient air box temp, and cycles the compressor (if power is available) to maintain that temp…A good Hold Over system only senses Plate temp (to keep the plate frozen) in order to save energy, and thus the box temp…Is what it is…Depending on all the factors I have mentioned…

Thing is…Boxes, doors, gaskets & insulation are almost never perfect…Especially as they age…So as you might see…Maintaining these marginal temps for food storage is very critical, and a chore for the owner of such systems…Most never utilise the real design of the system as a hold over system so to speak…They generally end up adjusting the thermostats to get the box temp they want and leave it at that…Thus running it like a conventional system…Which it is not as good at as one designed to operate that way.

Knowing all the advantages & disadvantages is key…Yes Hold Over systems can still provide a long distance cruising option, but with things like today’s high efficiency DC to AC power inverters, or the little DC powered flat plate systems…A more standard system can offer the refrigeration you may be more accustomed to at less expense.

Steve~

I started this site last year to “put my feelers out”  about what owners and captains may want to learn and share about marine  a/c.

The support has been more than I ever expected…

So… My New Year resolution to you is expand the site we created…Because of your feedback I am going to begin adding to my store to allow you to order most of the common Marine A/C system items that I found you’ve needed,  but until the store is fully operational…As always I’m here for you to contact…

Some important information…Sadly…Due to EPA regulations there will be no more R-22 systems/units produced in 2010…

• If you need to replace a R-22 condensing unit in an existing system…You will need to purchase a R-417A unit, evacuate your R-22 (which you would do anyway) and re-charge the system with R-417A (drop in replacement for R-22)…No need to change the air handler.
• For new installations (split system or self contained) the systems have been re-designed to operate with environmentally friendly R-410A which operates at much higher pressures that the existing R-22 or R-417A systems…These R-410A units can Not be paired with the older air handlers.

Your local A/C guy will know what to do & have the equipment to make the change.

Your comments & feedback are always welcome & appreciated…I need things to help me write…So ask away…It does stir the thoughts…

Clean Sea Strainers to All, and to All a Good Year…Think of the A/C/Heat/ Refer Guy…He Does You…

Steve~

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)

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 individualised 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 controlled 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.

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 http://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~

These two-stage systems use circulated water as a heat transfer medium. The warmed or cooled fluid is piped through a closed loop from the tempering unit in the engine room to any number of air handling units throughout the boat.

Dometic’s unique reverse-cycle design provides very efficient heating, even in relatively cold seawater temperatures, in many cases eliminating the need for separate heating systems.

Dometic offers a complete line of single-compressor and staged multi-compressor systems from 1.5 tons up, utilizing state-of-the-art compact modular tempering units.

We offer local Service & Sales here in the Tampa Bay / West Coast Florida area…

We also offer help on the forum http://marine-ac.com/forum/ with any troubles you might be having or not understand…Just drop us a line or two. Or just Contact Steve here…