There’s been a scramble for the past eight or 10 years for a replacement for Freon 12 (which is now banned) in refrigeration systems. Many marine suppliers have been using a refrigerant called 134A as a substitute for Freon 12.<\/p>\n
The problem is that 134A is significantly less efficient than Freon 12. The technical literature indicates 10-15% less efficient-but our own unscientific estimate is that it is more like 20-25% less efficient in our marine applications.<\/p>\n
Fast forward to a couple of months ago when our friend Richard Findlay, a retiree from the heating and air conditioning industry (Richard is currently on the last phase of converting the breakthrough racing yacht EQUATION to a cruiser) sent us some technical info on a Dupont product-MP-39.<\/p>\n
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He had been doing research on what to use on his boat, and a friend of his who has been replacing Freon 12 with MP-39 in commercial applications turned him onto this material. Turns out it has been around for years and used in thousands of commercial coolers and freezers around the country. The tech data from Dupont indicated a 20% gain over 134A and a 10% gain on Freon 12.<\/p>\n
You can change it out, using the same expansion valves. The only issue is the oil in the system. It works with POE, with which many marine compressors are shipped (and which is a requirement with 134A), but you need to check what you have and the compatibility (and pull the old oil if it is not compatible).<\/p>\n
Since we have two parallel systems on BEOWULF we decided to charge one compressor with the MP-39 and see if there was a difference. We noticed a quicker pull down and similar amp draw, so we went ahead and changed the second compressor.<\/p>\n
Based on checking running time, it looks like we’ll have a lot better than 20% gain-perhaps as much as 30%-over the 134A we’ve been using. It is going to take a couple of weeks of watching the fridge\/freezer plates and temperatures to dial in the optimum settings. MP-39 pulls the plates down much more quickly, so we suspect that we will need to reset the cut in temperature and differential temperature for optimizing power consumption.<\/p>\n
One caveat-if you do go this route, filling the system with refrigerant (after vacuuming out the old material) is quit different than what you are used to. MP-39 must be introduced into the system as a liquid (rather than a gas as is normal with other materials). Finding the correct charge is done with high and low side pressures-Dupont has a brief tech sheet which describes the process. You cannot use the sight glass, as a full charge of MP-39 will result in bubbles-i.e. what would appear as an undercharged system with 12 or 134A. It is not difficult to charge the system, it just takes a couple of hours.<\/p>\n
We had heard rumors from local “experts” that MP-39 increase the head pressure and compressor loads. However, we have not seen this. In our installation (water cooled) head pressures are up about 5 to 10 pounds over what we experienced before too-the system now runs at between 95 and 120 pounds depending on where it is in the pull down cycle.<\/p>\n
If you want a more efficient fridge\/freezer system, check out Dupont’s MP-39 refrigerant.<\/p>\n
*****<\/p>\n
Since we posted information on our experiments with Dupont MP-39 some weeks ago we’ve had quite a few comments and questions. Apparently some of the marine “experts” are saying this gas is no good. We’ll let them debate that with Dupont, who says it is way better. What we know from our own real world use aboard BEOWULF is that we are seeing significantly better efficiency. That’s good enough for us.<\/p>\n
There are a couple of caveats: First, you or your technician has to know how to load this refrigerant into the system. This process is totally different than what you\/they are used to with F12 or 134A. Should you decide to give this material a whirl, you will see below detailed instructions on its use from our friend Richard Findlay, who turned us onto MP-39 in the first place.<\/p>\n
The second caveat is that you need a water cooled compressor-most are, but if you have an air cooled system it is likely the head pressures will be too high.<\/p>\n
OK, Richard’s comments follow (he’s been in the heating and air conditioning business forever-so he knows what he is talking about-and he is a cruiser as well) and he put them together for us should we ever need to recharge BEOWULF’s fridge systems.<\/p>\n
*****<\/p>\n
MP-39 is a replacement for R-12; it is 10% more efficient than R-12 & 20% more than 134A. Because of the higher pressures & discharge temperatures I only recommend this for liquid cooled condenser applications. <\/em><\/p>\n All 134 or R-12 must be removed from your system and an oil change made if necessary. Replace the filter dryer. The system should be evacuated to 29.9 in. HG; this removes all the air & moisture from the system. You can find more info on recommended oils & complete step by step MP-39 refit at the official Dupont website http:\/\/www.dupont.com\/suva\/na\/usa\/literature\/index.html.<\/a> <\/em><\/p>\n The method I used to get the MP-39 into BEOWULF’s system is as follows: <\/em><\/p>\n 1. Turn the compressor off, close (backseat-turn counter clockwise) both valves on the compressor. <\/em><\/p>\n 2. Hook up your gauge set lines to both sides of the compressor & hook up the gas line to the MP-39 tank. <\/em><\/p>\n 3. With the refrigerant can in the upright position purge all air from the lines by opening & then closing the tank valve & then bleed the lines at the compressor. Tighten the hoses before all of the pressure is gone. A small amount of gas will be lost but all air in the lines must be purged.<\/em><\/p>\n 4. Open the high pressure valve on the compressor to the service position. Turn the refer can upside down & open the valve to allow liquid into the line. Now open the high pressure side (red) on your gauge set allowing liquid to flow into the high pressure side of your system. When the refrigerant stops flowing close the gauge valve. The system should be 70% to 90% charged.<\/em><\/p>\n 5. With both gauge valves closed open the suction valve on the compressor to the service position.<\/em><\/p>\n 6. Start the compressor & balance the system so that your discharge pressure is about 10-20 pounds higher than your R-12 system or 20-30 pounds higher than your 134 system. The suction pressures should be the same as R-12 & 3 pounds less than 134A. Don’t use your sight glass with this refrigerant, it doesn’t behave the same as a single component refrigerant. You will want to have a Pressure-Temperature chart to estimate the actual temperature of the suction line at the holding plate(s). You may now add refrigerant to the suction line by cracking the suction gauge (Blue) valve a small amount so the gas exits the tank & gauge as a liquid…but it must boil into a gas before it reaches the compressor. If any liquid does reach the compressor, it will run very rough. Too much liquid may break the intake valves, in which case you will have to start over after you replace the valve-unless you have a hermetic compressor, in which case you get to buy a new one. Take your time & add it very slowly. MP-39 is much more sensitive to overcharge than R-12 or 134A but the pull down times are a lot faster once you have it dialed in. <\/em><\/p>\n","protected":false},"excerpt":{"rendered":"