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For many years Hold Over/Cold plate refrigeration was the way to go for long distance cruising yachts, and over the road refrigerated trucks…The function is Just as the Phrase Implies…Hold Over…For extended periods with a minimum of refrigeration system run time.

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~

Since they are not like home A/C controls…Sometimes marine A/C controls are misunderstood…Hope this can clear up some misconceptions…

They do provide the same function as in home systems as they are designed to keep the temperature in the cabin/room at a selected temp within a few degrees…

But different than Home…They can (and most do nowadays) offer more/different features than we use at home depending on the type of marine control that is installed…We can cover some of those features here but first we need to define which type of control is installed…Although there have been and are many types and models of controls with several variations…

Lets first describe the most popular two main types…

Manual Controls…

The old standby that has been around for many years is the three knob manual control (non digital) it has/had 3 control knobs each with a different function & was/is available in either a vertical or horizontal, rectangular form factor…

The typical function of each knob was as follows…

• The first knob was a function knob with Off, Start (sometimes labeled Fan) and Run positions…

The functions of each position were pretty much self explanatory except that the Start/Fan position ran the fan but also started the seawater pump so that you could look over the side of the boat to verify it was pumping water before selecting Run.

The Run position sent power thru the thermostat which then would decide whether to start the compressor in the cool, or heat mode depending on cabin temp, and the position of the thermostat knob…(more on that in a minute)

• The second knob was a Variable Fan Speed control (not usually available at home)

It was useful at night for lowering blower noise to watch TV etc…(how low was low was adjustable but the control needed to be removed to adjust this parameter with a small screwdriver)

• The third knob was the thermostat…

This was the most misunderstood function of this control because it had no temp numbers (It was also the hardest to explain to folks)  Most would just crank it to it’s coldest setting thinking that the further they turned it…The colder the air would come out…That’s true in a way, but it’s not a function of the control, and A/C does not work that way…I will try to explain…

Regardless of control setting or type…All R-22 A/C systems work on a 15 to 18 degree temp exchange design…Meaning that the air coming out of the discharge grill should be 15 to 18 degrees colder than what is going into the return air grill (if it’s more, or less than that, there is likely a problem with the system or installation)

So if it’s 90 degrees in the space being cooled…don’t expect much colder than 75-72 degree air coming out the discharge with any R-22 A/C system…But as the room/cabin cools, that exchange is maintained, and the air continues to come out colder by 15 to 18 degrees of what goes in….Lower room temp=lower discharge air temp.

The thermostat tells the compressor when to run or not run, and energizes the reversing valve when reverse cycle heat is needed to maintain cabin temp of the setting on the dial (position of the arrow)…Generally speaking…A properly calibrated t-stat set with the arrow pointed vertical should maintain around 70-74 degrees cabin temp…Anything to the right is a colder cabin, and to the left of vertical is warmer…The T-Stat will allow the compressor to run until the cabin gets to the selected temp (on the knob) at which point it cuts power to the compressor until the cabin either warms or cools a few degrees, at which point it then again sends power back to the compressor/reversing valve as needed to bring the cabin back to selected temp.

These controls offered very little in system protection and thus it was not advisable to run the A/C system unattended for very long.

Digital Controls…

Started hitting the market in the mid 80’s…They at first like any new product, had a few weaknesses and thus some early problems, but as they matured they have now become the standard, and are very reliable…

 They also allow the marine A/C manufacturers to offer extended warranty periods when installed with new equipment because of the system fault protection/shutdown features they provide, along with the many other benefits/features…I can’t count the compressors & pumps they have saved for my customers…Many of them don’t realize it either, but they do help immensely…

The features & protections offered by these newer microprocessor based cabin/system controls are likely too many to mention here but I will list some of the more important below…

Protection:

• High Pressure Shutdown…Loss of Seawater flow…This can save a compressor and or seawater pump failure, from running without water. (Did you check that strainer & thru hull ?)
• Low Pressure Shutdown…Loss of Freon or a dirty air filter…Can also save a compressor….
• Low AC power Shutdown…One of the worst things for a compressor is low voltage.
• Seawater Pump shuts off with compressor (on single system boats) so that pump can be saved from no water burnout of pump head (this will also protect pump if only one system is run while away on multi system boats)
• Programmable Time Delays…So that multiple systems don’t all start at once when shifting from Shore to Gen or vise verse causing tripped breakers and/or heavy surges.

Features:

• Digital Display of Setpoint (Temp you want the cabin to be) & Actual Temp of that cabin.
• Much more accurate temp control. (when compared to the 3 knob control or others)
• Automatic Fan Speed control…Fan speed can be controlled by how far away you are from setpoint…Manual speed is also an option so that if you don’t want it to change it won’t.
• Ability to program Continuous or Intermittent Fan (Like the Auto fan feature at home)
• Humidity Control program…System can be activated to remove humidity only while away..This greatly reduces run time while keeping mold out (you probably won’t find this feature in most home controls)
• Some have IR remote control availability/operation.
• Some have networking ability…So that they can all be linked and controlled from a central (keypad) location, or from any individual control location aboard.

These are some of the most important features, but the controls are fully programmable for many more user adjustable functions (depending on model)

If you have one or more of these digital controls…The not so funny thing I find here in West Central Fl…Is that about 95% of the boats I go on have never had the digital controls setup for the boat/installation…

The A/C manufacturer has a set of Default settings they ship the controls programmed with…These are just that…Defaults that the manufacturer feels that all systems should operate safely with once installed…It’s generally thought that it’s the installers responsibility to perform the calibration…Unfortunately it’s likely that the boat builder or original installer did not do this for many reasons…One of which might be they don’t know about them ?…

Anyway as I said…Most of the boats I go on still have the factory defaults set in the controls, and a lot of these boats are many years old…They are by no means the best settings for each installation or system, and again if you have these controls, you may find that you will enjoy your system/s much more if you get your trusty A/C guy out to to go thru them…Or get the manual out yourself to take a look….

Many also ask if the newer digital controls can be retrofit to take the place of others…Yes they can…I have installed them on just about every application of marine A/C made in the last 40 years…Yeah…That’s longer than I have been working on marine A/C but I do/have seen some old stuff still in operation…and Usually after we install one on a boat and calibrate it…The owner almost always wants another…

Thanks for reading, and Comments are always welcome…

Steve~

First & Foremost are Filters…and not just the Sea Strainer I talked about in my last article….But the ones in the Return Air path too…

Direct Expansion A/C (as opposed to Chilled Water) systems rely heavily on good air flow to keep from icing up in the cool mode (Low pressure) or shutting off due to High pressure in the heating mode…

Generally speaking…Most boats may have two Return Air Filters per system or control…Some have more if there are more than one air handler on that system (compressor)

Without water flow….You have NO cooling !
Service people on the docks (at least the better ones) can walk down the dock during the summer and tell which boats they are likely to be getting a call from next just by the flow of water (or lack of) going overboard on each boat….Lack of seawater flow can cause other problems besides loss of cooling…

I’d like to say hello and offer my plans for this site…

First & Foremost…True to my history in the marine maintenance and air conditioning business…I’d like to help the boat owner with their A/C & Refrigeration systems.

I am always happy to share my experience, from the most minor advice…To major cooling or refrigeration upgrade plans…Questions will always be welcome on this site, share your thoughts and experiences, join the conversation about marine A/C maintenance and repair.  Together we can work towards making your boat cooling projects easier to understand and hopefully remove some of the mystery of how things work.

I will gladly answer questions on many subjects, including confirming what you are being told by your technician or helping you to understand what you can do yourself (If you are handy)

Steve~

Marine-AC.com is a new website for Cooler Marine Services. Steve Pooler of Cooler Marine has been servicing yacht air conditioning on the West Coast of Florida for nearly 21 years and in the recreational boating industry for 33 years.