In my kitchen at home we use cooking pots and pans made from a variety of metals, and I thought it would be an interesting project to delve into the pros and cons of each material and then go on to see how that works with refrigerator evaporators.

After all, cooking pots and fridge evaporators both utilize metal surfaces to transfer heat, so many similarities exist.

When cooking on the stove, we're conducting heat from an external source (the burners), through the material of the pot or pan to the contents in the interior.

Simple enough you'd think, but different metals have different characteristics, and work in different ways. The ability of a material to transfer heat is known as its Thermal Conductivity. This is quoted in various units, but here we'll use good old fashioned BTU's per hour per foot per degree Fahrenheit (Btu/hr-ft-F).

Listed below are some of the common metals used for cooking pots and pans together with their Thermal Conductivity rating, starting with the most conductive and ending with the least. Basically, the higher the number, the more heat the material will conduct through it

There has long been a debate about air cooling versus water cooling for marine refrigeration systems. Water cooling has traditionally been generally accepted to be between 25% and 35% more efficient in warm/hot ambient conditions, but some of that efficiency gain has to be offset by the energy required to run a water pump.

The Frigoboat Keel Cooled system is water cooled and does a fantastic job without the need for a fan or a pump. That will be mentioned later, but the following compares air cooled systems to traditional water cooled systems using sea water with a pump.

Many boaters these days seem to be opting for air cooled refrigeration systems even though they’re heading south into hot climates, and despite the notion that air cooled is inherently less efficient than water cooled. Why is that?

Inner Secrets of the Danfoss/Secop BD35/50 Motor Controller (aka Module)

Well I can't actually give away any real secrets, because I don't think anyone really knows what goes on under that mysterious black plastic shell except for the manufacturer, but I do know a fair bit about what can and does go wrong with them.

But first let's take a step back and recap on what the little black box actually does.

The current generation of small, mobile refrigeration compressors from Secop (formally Danfoss) utilize a very simple motor with just three equal windings and no brushes or slip-rings. These three windings terminate in three pins that protrude from the compressor shell and connect to a push-on plug connected to the controller.

It's the controller's job to take the 12v or 24v DC input and spit it out in sequence to each of the windings in turn, causing sufficient torque to turn the rotor and so push the piston in and out compressing the refrigerant gas. So the motor actually gets a modified DC signal, a form of AC in fact, and by varying the rate of delivery of the signal to each winding and effectively altering the frequency, we can make the motor turn at different speeds.

That's it. All pretty simple in theory. As a means of altering compressor speed, the controller uses the switched input from the thermostat, and by adding resistance to this circuit it alters the speed at which the compressor will run.

So what could possibly go wrong?

Did you know that if you store wine at higher temperatures than 65°F, you will actually be accelerating the aging process? Conversely, storing wines at colder than 45°F means they will not fully develop, robbing the wine (and yourself) of its full potential. Even that inexpensive bottle of Chardonnay you bought on sale last week can be adversely affected by storing it under your boat's salon settee until you've made room in the ice box, which in itself is normally at 40°F, so not a good place to put your wine anyway.

The temperature at which you store, and serve, your wine will have an impact on its flavor and your enjoyment. Especially if you plan to store your wine for at least 6 months, you know, for that cruise you've been planning to take before life gets in the way. On my boat, wine doesn't last long in storage, but that doesn't mean I want the taste to be compromised because I didn't handle it correctly. Something that could be so easily fixed.

"Icing Down the Beer" vs "Beering Up the Ice"

Here's a fact: Heat travels in one direction only; from warm to cold. So if a temperature difference exists between two items, the warmer item will lose heat to the cooler item; so the warmer item gets colder, the colder item gets warmer.

Simply put, when we put warm beers into a cooler of ice, we don't actually cool down the beer as much as warm up the ice! When heat leaves the beer for the ice, the beer gets colder as a result, and soon the contents are all at a wonderfully refreshing 32F temperature. And thanks to the laws of science and beerology, everything will stay that way until all the ice has melted and the beer has been consumed.

But what about your refrigerated ice box? Isn't it always being kept cold?

Are you, or is anyone you know, a Temperature Control Freak? You know the type; constantly fiddling with air conditioning and refrigerator controls and reporting on them to anyone within earshot. Well, I have such a friend.

TCF, as we will call him, has a digital temperature controller/thermostat and tells me that 39.2°F is the perfect temperature for his fridge. How he comes to this conclusion is beyond me, and quite honestly I don’t want to ask. Suffice to say that he’s happy with that after several months of laborious experimentation. And then there is the freezer ...

Now a fridge can only be between a narrow band of temperatures; too cold and it’s a freezer, too warm and it’s not a fridge. But a freezer can be kept at any temperature below freezing; from marginally frosty to cryogenic. It’s all down to how you intend to use it.

Foodstuffs will be preserved as long as they are frozen, but the appearance and edibility when thawed will differ with different temperatures and time. In Europe there is a star rating system for freezers as follows:

We handle many calls for troubleshooting help, and the vast majority end up being electric problems, mostly with the boat’s power supply to the Frigoboat unit. While the voltmeter on the distribution panel might show more than adequate power, it is what comes out of the end of the two wires at the Frigoboat unit that counts, and there is a lot of potential in the wiring for gremlins to creep in and spoil the party.

Power supply testing on Danfoss DC powered refrigeration systems

To properly test the power supply to a Danfoss/Secop powered 12v or 24v system, the following testing procedure must be carried out. This will establish whether the power supply feeding the system is free of bad, loose and/or high-resistance connections. Reading the voltage on the panel or at the batteries is meaningless,

Remember back when you had to defrost your home refrigerator every couple of weeks? It was a fact of life. And then those frost-free refrigerators came about. No more defrosting!!

So why have we seemingly gone backwards in evolution and are having to defrost our boat's refrigerator/freezer boxes so often? Why can't our boat's fridge be frost-free too, you ask as you drape your frozen food in towels to keep it safe as you patiently wait for the ice to melt from your evaporator plates.

Natural defrosting is the only safe method, although a small amount of addition heat is OK, say from a portable inspection light in the box. Those who are impatient might consider using a hair dryer or heat gun, hot water, or, (shudder), an ice pick, but these are not recommended, as high heat and physical force are very likely to cause nasty and highly undesirable side-effects.

And who gets the finger pointed at them as the culprit for this lack of frost-free living? Why, the refrigeration manufacturer of course, although after reading the following, you may shift the blame elsewhere.

Anyone with a refrigeration system on their boat or RV that is powered by a Danfoss (now Secop) BD35 or BD 50 compressor should be aware of the diagnostic diode function, which, with a simple flashing LED, tells you the fault reason that caused your compressor to stop.   Much of the following also applies to the BD80 compressor controller.

By connecting a simple 10mA 12v LED across the "D" terminal and a "+" terminal on the electronic controller attached to the compressor, you will have added a powerful fault-finding tool that may save you a lot of time and trouble later on.

Why the manufacturer elected not to incorporate a diode in the controller housing is anyone's guess, but Coastal Climate Control comes to the rescue here with three options:

1. A Coastal Diagnostic LED kit with an LED that you can either install permanently or keep in the spares kit.

2. A Merlin II compressor speed controller that also incorporates a diagnostic LED.

3. A Guardian digital thermostat/compressor speed controller that features a diagnostic LED

OK, so now you have some form of diagnostic LED installed, what is it going to tell you? If your fridge or freezer system unexpectedly stops working, i.e. other than the thermostat stopping the compressor, and you go take a look at the diagnostic LED, what exactly are you looking for?

Frigoboat's Keel Cooler, installed on over 40,000 vessels worldwide, offers water-cooled heat exchange for your refrigeration system without the use of a pump. This means no strainers to clean, no noise, and little maintenance.

The Keel Cooler is embedded in sintered bronze, which is primarily copper, making it naturally anti-fouling. Add to this the fact it is warm to the touch when in operation means there should be little sea growth on it.

However, in some areas the water is rich with algae and other sea life and a build-up can occur. Not a problem. Simply use a stiff, nylon brush or green scrubber pad to wipe the accumulation off the keel cooler. Pesky barnacles may require a plastic scraper, but please resist the temptation to use a metal scraper or wire brush. Both of these devices could harm the sintered bronze coating and potentially the embedded cuper nickel tubing containing the refrigerant.

There is quite a collection of Eco-friendly "Barnacle Buster" products that can be used to help dislodge crustations, but please read the instructions carefully.

If you have continued issues with excessive growth on your keel cooler, a single coat of anti-fouling paint can be applied with little to no noticeable loss of performance. Bear in mind, though, that you can then no longer use your keel cooler as a grounding plate for an SSB or other radio device.

Rest assured, your keel cooler should last the life of your Frigoboat system.

The couplings used on Frigoboat component refrigeration systems are proprietary to Frigoboat and are designed for long and trouble-free service. Some time ago it was noticed that there was an increase in reports of leaking o-rings, and many were found to be caused by the coupling becoming excessively hot, damaging the rubber in the primary O-ring. Causes of excessive heat can be:

- badly fouled Keel Coolers;
- using a Keel Cooled system when out of the water and without temporary water cooling;
- inadequate ventilation of an air cooled unit;
- poor or restricted water flow in a pumped-water system.

The type of rubber in the O-rings was subsequently changed to better handle excessive heat, but damage may still result if any of the above situations are allowed to prevail.

All compression refrigeration systems depend on some device to separate the high and low pressure sides of the system. In a capillary (cap) tube system, this is the capilliary tube itself, which, as the name implies, has an extremely small micro-bore at its center that is less than the diameter of a needle.

There are two main issues that can occur with cap tubes: a particle blockage at the high pressure end near the compressor (picture on the left), and a moisture, wax, or oil problem at the other next to the evaporator (picture on the right). The Guide below describes the symptoms and recommended remedies for cap tube problems.

Capillary Tube Troubleshooting Guide

It’s a boat. Something’s going to break, and if you’re in the middle of the ocean or in a deserted anchorage in Paradise, who’s going to fix it? There’s no handy-dandy repair chappie down the road, and no one to beg come and mend it, so if you don’t fix it, it stays broke. Simple.

For household appliances, whether in a terrestrial abode or in use on a vessel, things may soon be easier and cheaper to fix, thanks to proposed regulations being put forward in Europe and some 18 US states. Loosely termed “Right to Repair” bills, these would compel manufacturers to make products that come apart easily for inspection, and to have instructions and spare parts readily available to anyone wanting to attempt a repair.

Fast running refrigeration has its benefits, and it has a downside, too.

There’s quite a variety of passers-by to be seen from my front porch of an evening, and most seem to be walking a dog or two, or three.  The majority of walkers fit in a velocity band somewhere between comfortable stroll and brisk jog, but there are also those on the fringes of the extremes, and these are the most interesting to observe.

At the hyper-speed end is Speedy Meanie, and he’s a runner on a mission. He’s lean and long-legged, and usually shirtless (in Summer anyway). He and his hound bound along in perfect synchronicity and appear out of nowhere in a flash, so you need a keen eye to catch him. He’s well known in the neighborhood for having a bit of a mean temper, and woe betide anyone that dares to get in his way. If Speedy Meanie arrives just as one happens to be putting the bins out, one can get an earful of colorful curses if he has to maneuver around them.

At the opposite end of the scale is dear old Ambling Archie. Archie is a truly loveable little dog, and as well as being small, he is very, very slow. Unlike Speedy Meanie, it is Archie that controls the pace, which is excruciatingly slow and difficult to watch, while his companion digs around in his smart-phone for something interesting to help pass the time. Ambling Archie doesn’t go very far, just to the end of the block and back, but it’s all the exercise he needs, and it’s quality time for him and his master.

(as found in Section 6 of the Frigoboat manual)

The F-type flat evaporators may be carefully bent on a minimum 1.5" radius to follow the shape of the icebox. This is best done by holding a section of suitably padded PVC pipe (with an outside diameter of 3.0" or greater) firmly down on the plate, and then carefully bending the section upwards with the palm of your hand.

The stainless steel plates need more force to bend and may require the assistance of a second person. This must be done slowly and with great care to avoid excessive kinking of the channels in the evaporator.

Never attempt to bend a plate downwards over a pipe, as damage may result.

In order to prevent the paint from cracking, the area to be bent should be warmed with a hair dryer or heat gun to approximately 200 degrees F before bending.

Once upon a time, a long time ago, there was only one brand of refrigerator that would work on 12v DC boat power. There must have been many thousands of them out there back in the day, predominately on powerboats, and a lot still exist to this day.

These refrigerators have one or two compressors typically mounted on the rear of the cabinet, and these compressors require 20v-30v AC for their operation. When 115v AC mains power is available, either from shore power or a generator, the power for the compressor(s) is supplied by using a simple transformer to lower the 115v AC down to the lower AC voltage required by the compressor(s).

But when the boat unplugs from the dock or the generator quits, the compressor is then powered from a built-in inverter that produces the required low voltage AC from the 12v DC supply. Due to losses inherent in inverters and the desire not to involve electronics unless absolutely necessary, these fridges would always be supplied with separate wiring for connection to both 115v AC and 12v DC, with the system automatically switching to 115v AC if it is available.

Fast forward to modern times, and we are now blessed to have marine fridges utilizing the super-efficient Secop (formally Danfoss) compressors that are powered by 12v or 24v DC. Under normal circumstances, when the vessel is at the dock and plugged in to shore power, the battery charger will be on and supplying the DC power for the fridge. The batteries are not involved in this process, as the DC from the charger does not go into and out of the batteries, but is supplied directly to the fridge from the charger.

In this situation there will always be 12v or 24v DC available, but if circumstances dictate that the charger will not be left on, or that at times there will be no 12v or 24v DC available,

1. Box no longer reaches desired temperature set point

A refrigerator box should be kept at 35-40F for safe food storage. If your box used to do this, but doesn’t anymore, then you could have insulation degradation, perhaps your thermostat isn’t telling the compressor to turn on when the box gets warmer, there may be a refrigerant leak, or your system may simply be showing its age.

2. System works sometimes OK, sometimes not

You can bet your bottom paint that everything will be hunky-dory for month after month, and that the gremlins will strike on the first day of your annual cruise with all the family on board. Time to get proactive and get the fridge fairies on your side with a nice new, shiny ,reliable, fridge system.