Diycooling kit

If the performance of your boat’s fridge is less than satisfactory, you might consider boosting it with an easy-to-install, 12-volt kit.

Until relatively recently marine refrigeration was typically powered by the main engine via a belt-driven compressor. These systems usually comprised a standard, automotive air-conditioning compressor, a custom-made, water-cooled heat exchanger and a locally-manufactured stainless steel cabinet. The system’s weak link, obviously, is this: if the engine’s not running neither is your refrigeration, and every time you extract food or drinks the fridge loses cooling performance.

As luck would have it, there is a relatively inexpensive kit to supplement and improve the cooling system. This kit comprises a small, aluminium cold plate (evaporator), a Danfoss (Secop) Direct DC compressor and a thermostat – and it retails for under $1,000.

As a supplement to the existing mechanical system, you’ll have a no-nonsense, air-cooled refrigeration system that will maintain your fridge 24/7.

Follow the instructions below to install the kit into an existing fridge.

INSTALLATION

The most difficult part of the installation is drilling an access hole (from inside of the fridge) to take the connecting pipe between the evaporator and the condenser. The evaporator is the aluminium plate mounted inside the fridge, and the condenser is the motor compressor that removes the heat. Crucially, you want to drill the hole through a ‘safe’ or ‘clear’ wall.

In most cases a marine fridge has a cold brine tank built

into the back wall. The side walls, as well as the cabinet’s top or bottom surfaces, are usually the safe walls for drilling an access hole. If you run the engine-driven system you can see which fridge wall frosts up first – a good clue to identifying which wall has the tank – and which should therefore be avoided (seek advice if you’re still unsure).

Before we go much further I should explain the purpose of a brine tank. It contains both copper tubing and a liquid that won’t freeze – though it does absorb lots of energy. This liquid is usually mono-ethylene glycol, automotive anti-freezer, methylated spirts or even sugar and water. You don’t want to puncture it – the engine-driven system will fail!

An engine-driven compressor develops a huge amount of cooling energy that cannot be transmitted into the fridge all at once. So the system uses a ‘liquid pillow’ that’s built into or mounted on the fridge wall to absorb energy and then slowly release the energy over the next few hours.

Start by drilling a 5mm pilot hole (with the drill set to a very shallow depth stop) into the selected stainless steel wall. Once you’ve got a pilot hole, use a bit of wire to probe and make sure there are no copper lines lurking behind. If there are, repair the hole with a 5mm blank rivet and try a new hole in a different wall.

When you’ve got the all-clear, you can complete the process by cutting a larger hole – use a 32mm hole saw – around the pilot

hole. Stainless steel, remember, is a hard material and takes a good quality hole-saw, slow speed with the drill, cutting fluid and some good old-fashioned grunt.

The new cold plate’s couplings and connecting line will pass through this 32mm hole. Before drilling the hole, also consider where the couplings and connecting line are going to exit. If possible, try to have the hole ‘emerge’ inside a locker so the lines are not seen.

Take a breather – you’ve just completed the hardest part of the install.

MOUNTING THE NEW COLD PLATE

You’ll have to decide which of the fridge’s inside walls to use for mountingthenewaluminiumcoldplate.astheplateandplasticspacer strip is less than 15mm deep, the plate is often mounted on the back wall of the fridge – in front of the existing brine cooling plate.

After mounting the plate, shelves can be cut down to suit the new internal size. Because you can’t drill into the existing tank for mounting the new plate, I use 3M’s VHB adhesive tape.

I use 20mm x 10mm thick plastic strips (vertically) on the selected wall.

The trick here is to make sure the fridge is warm and moisture free. Clean the stainless surface using thinners or acetone. To warm the cabinet, use an electric heat gun or a blow drier. With the stainless warm, the 3M tape will stick well and won’t release when the cabinet is cold.

THERMOSTAT TEMPERATURE CONTROL

The thermostat control fitting can be mounted inside or outside the fridge. Once the unit is running you very rarely need to adjust the thermostat.

The thermostat controls the fridge plate’s temperature and requires the sensor tube to be connected to the plate. The kit comes with a mounting clamp. The electrical cable is then passed to the compressor where the electrical spade terminals are pushed on to the clearly-labelled spade pins – T, C and a loop wire on to P. The loop wire is to allow the compressor to start up on a low battery voltage.

COMPRESSOR

The compressor is also an easy mount. The trick here is placing the compressor in a position which receives good ventilation. Remember: half the job is making the food cold; the other half is getting rid of the heat the refrigeration kit has removed.

Placing the compressor in a locker with a small vent in the front won’t do. You need flowing ventilation where the air can come in one aperture and exit through another. This is very important: a lack of ventilation equates to lots more battery power.

The kit comes with a compressor-mounting bracket which can be fastened to the wall or floor. The compressor simply drops onto the mounting pins and is locked into place. The connecting pipes are tightened using a pair of crescent wrenches.

These fittings don’t need any thread tape or Loctite solution – they should be nipped up tight. They are designed to be selfsealing so you can undo them again if necessary. Try to coat the bracket and compressor with an anti-rust product for protection.

ELECTRICAL SUPPLY

Next – hook up the power supply, using 5mm wire to prevent any voltage drop. The kit comes with a 15-amp fuse but I prefer to use the circuit breaker on the switch panel if possible.

Finally, turn on the unit. The kit is pre-charged with refrigerant so it’s all good to go. This system will keep your food at a good temperature while the engine-driven unit is at rest.

Another advantage of the kit is that is can be run off shore power, if this is available at your berth. We can supply a mains power module to run directly from shore power. Alternatively, install a 120-watt solar panel. In summer this will keep the fridge going without external mains power. Sadly a week of winter rain won’t allow the solar panel to support the fridge.

The fridge kits require no annual servicing and are good for more than 10 years. B

the engine’s asleep.”