Recharging your Refrigerator
A marine refrigerator is wonderful thing— as long as it’s working. Photo by Charles J. Doane
Ever had refrigerator angst? It’s a dreadful state of mind that consumes you when your reefer doesn’t deliver the goods. It’s been known to paralyze cruisers for weeks on end, trapping them in exotic ports while they lay in wait for that rare, elusive creature known as a marine refrigeration technician.
I suffered it myself for a short time last summer, after I accidentally discharged the refrigerant from the new fridge unit I had installed. Several months later, after having been repeatedly let down by not one, but two different professionals, and suffering a summer of having to tote heavy coolers on board—the very thing I’d hoped to avoid by installing a fridge—I decided it was time to man up and do it myself.
Reading assorted treatises on marine refrigeration only elevated my angst. Various experts on web forums warned direly of the dangers of getting air into the system, failing to purge the refrigeration gauges, overcharging with refrigerant and blinding oneself with escaping gases.
On the other hand, I knew that topping up the charge in a car’s AC system is such a simple DIY task that the refrigerant and hoses are readily available in auto-supply stores. Surely, if any doofus can top up a car’s AC system, any doofus should be able to top up a marine fridge? It was time to find out.
It helped that I knew why my fridge needed a charge: soon after installing the Isotherm fridge unit I had undone one of the Danfoss BD35 compressor’s quick-fit couplings to make room for the galley sink drain hose, and heard a distinct hiss as the gas made good its escape. Had there been an unidentified leak, the repair would have involved tracing and repairing it, then sucking air and moisture out of the system with a vacuum pump before recharging. More than likely, this would have required the services of one of those elusive professionals.
1 I ordered a single gauge and hose combo from great-water.com—it was expensive, but cheaper than paying a fridge mechanic (had I been able to coax one out to the boat), and it came with clear instructions. I bought the R-134a refrigerant over the counter at an auto parts store. This setup can be used to recharge any system with a Danfoss compressor.
2 The fridge is recharged via a valve mounted at the end of a short stub on the suction side, clearly identified by the green shrink-fit tubing. It’s a Schrader valve, like those used on common bicycle tires.
3 Following instructions, I ran the compressor for 15 minutes to warm it up, with the thermostat set to the lowest temperature—this keeps the compressor running at a constant speed. Then I connected one of the two valves on the charging kit to the refrigerant canister, making sure the other one—the manifold valve—was closed.
4 After opening the dispensing and manifold valves just long enough to purge air out of the hose with refrigerant, I turned off the manifold valve and connected the hose to the Schrader valve. It was now the moment of truth.
5 With the compressor running, I opened the manifold valve and let the compressor suck in the gas for five seconds or so until the gauge indicated 20 psi. To avoid overcharging, it’s best to charge in short bursts and let the system settle down for a few minutes in between. For an evaporator system like this, the pressure will drop to 3 to 7psi as the box cools down. Holding plates will show a higher initial pressure, 10-15psi, and then drop to under 10psi.
6 After a few minutes, the pressure dropped to 7psi and then down to 3, so I gave the system another 5-second charge. By the way, it’s important never to tip the can upside down while you’re charging. Otherwise, its contents will emerge as a spray of freezing liquid.
7 Holding steady at 6psi, but I figured a bit more refrigerant would not hurt. Another 5-second blast brought the pressure up to 10psi. Once the box was fully cooled down, this would almost certainly drop to 7psi or thereabouts.
8 The wonderful sight of frost forming on the walls of the box brought a smile to my face. I checked for overcharging—indicated by frost forming on the suction tube more than a foot from the evaporator plate—and all was well. You don’t want to release R-134a into the atmosphere, which is one reason to avoid overcharging by topping off the charge in small increments. The refrigerator has worked perfectly since its recharge.
Photos by Pip Hurn