Over the last 25 years, there has been a dramatic shift in the types of refrigeration systems carried aboard cruising boats. Today, 12 volt systems prevail, but the systems most often installed up to the late 90’s were driven by the main engine. Engine drive refrigerators function just like the air-conditioner in your car. A belt driven compressor forces a refrigerant gas through a typical vapor-compression cycle. Though it’s often one of the less understood onboard systems for boat owners, these engine driven systems only consist of a few key components. A compressor with a clutch activated by an electric timer, a condenser (usually water cooled by the engine’s raw water pump), an expansion valve, an evaporator (inside the holding plates), and some lengths of copper tubing.
Diagram from SAIL Magazine
One of the key advantages to the engine drive systems is that they are self-supporting. Since they don’t rely on an electric compressor, there is no additional drain on the batteries. However, unless an engine drive system is fitted with a secondary electric compressor, the engine must be run each day to keep the fridge cool. This is a problem for boats that spend most of their time at the dock. However, for active cruisers or charter boats, an engine drive system perfectly satisfies the need for reliable and powerful refrigeration. According to Cleave Horton from Sea Frost Refrigeration, “People that still have them (engine drive systems) love them.” Nigel Calder, author of the Boatowner’s Mechanical and Electrical Manual, feels similarly, saying to me, “Hang onto them (engine drive systems) as long as they keep working OK and then rip them out the minute they begin to act up in any kind of a way that requires the system to be opened up.”
It’s true that engine drive systems can be very expensive to repair. Cleave reminds me that many of these legacy systems cost as much as $10k when they were originally installed on yachts valued over $250k. However, 30 years later the same boat might be resold with aging systems to a new owner for less than a quarter of its original value. To the new owner, the thought of spending thousands to repair an engine drive system is simply not practical, regardless of its initial value.
If your boat has a non-functioning engine drive system installed, it probably makes more sense to replace it with a newer 12 volt system. Nigel Calder again explains, “The pre-charged (12v) hermetic systems are not that expensive any more, are pretty efficient, quite powerful, and relatively easy to install.” However, let’s remember that the engine drive system was self-supporting, it did not place any extra drain on the house batteries. If your boat has not already upgraded its electrical system with sufficient battery capacity and charging sources for extended time away from the dock, you must consider this cost when adding 12v refrigeration. Adding a refrigeration unit without sufficient means to support the electrical load will cause many headaches and a much greater strain on your wallet in the future.
Are there still times when it is cost effective to repair your engine drive system? I believe the answer is yes. If a system hasn’t been abused by running without a charge, it’s been kept clean (and free of corrosion) you can probably bring it back. If you can assess what’s wrong then a more educated decision can be made about whether it should be repaired vs. replaced. Here are some general steps to follow to help determine the status of your system.
1. Check for corrosion. Do the components and tubing look like they’ve been bathing in salt water for 20 years? Be sure to check under any insulation that covers the tubing. Corrosion leads to leaks. If your components are badly corroded, I would stop here. Remove and replace with a new system.
Sea Frost Compressor3. Check the clutch. With the engine off, engage the fridge timer or switch. An indicator light should be lit to ensure the power is on. You should hear a click. Try to spin the faceplate with your fingers, it should now be locked in place, unable to turn. If it still turns, be sure you have power to the clutch. Did the wires fall off? It should draw about 3 amps. When the clutch coil fails, it draws more current. Do you have a bad clutch? Stop and replace it. Did this fix your system? A new clutch coil can be found for $30 - $50.
Sea Frost Clutch Coil
5. Check the sight glass. Follow the copper tubing from the engine compartment to the ice box. A quality system should include a sight glass that you will find along the way. The sight glass is a little window for viewing the flow of refrigerant. Position yourself so you can look into the sight glass. Meanwhile, have a friend start your engine and rev to a high idle (900-1200 rpm). Then have them engage the fridge timer or switch to activate the compressor clutch. The engine should load up and slow down just slightly. While monitoring the sight glass continually, you should see a white foam develop, then transition to clear. If you do not see any foam, shutdown the system immediately as it does not contain a charge. If the foam is present but does not transition to clear, the system is low on charge. Take note of this behavior and continue to step 6.
6. Find leaks and recharge. Congratulations, you have a leak! Fear not, some leaks are no big deal. If your system has been sitting for many years, you might have a tiny leak from a fitting that was never properly tightened all the way. A system that has a slow leak of only an ounce of gas per year may hold its charge for quite awhile. A faster leak is an indication of corrosion in the system (refer to step 1). Courageous DIY’ers may be able to take this a step further and find the leaks and recharge without paying for help. However, if you’ve made it this far, I do not recommend replacement. Instead, pay a refrigeration professional to recharge your system. Communicate your findings from the first 5 steps to prevent them charging extra for time spent repeating your diagnosis. Your system may work just as well as it did when it was new!