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Date:         Tue, 18 Aug 1998 09:29:26 -0700
Reply-To:     Bill Davidson <davidson@SIERRA.NET>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         Bill Davidson <davidson@SIERRA.NET>
Subject:      Fw: Dometic
Comments: To: Vanagon List Address <Vanagon@VANAGON.COM>
Content-Type: text/plain; charset=ISO-8859-1

---------- > From: Bill Davidson <davidson@sierra.net> > To: Carter <carters@thegrid.net> > Subject: Re: Dometic > Date: Tuesday, August 18, 1998 9:28 AM > > Kit: > It's hard to stress strongly enough how important the inside fan and > packing of food for airflow are! (More important the extra fans behind the > fridge!) You can have a fridge that is working perfectly and still not have > cold food if there is not adequate air circulation inside the fridge! I > pack the bottom pretty tight and make it a point to leave the middle of the > center shelf clear except for the fridge fan. Pay particular attention to > the use of plastic bags which tend to spread out and form natural blocks to > airflow! > > Regarding adding 12v fans to the back of the fridge: > First I have to acknowledge Derek Drew because I got some of my ideas and > much of my inspiration for working on the fans from his article > "Refrigerator Madness." Thanks Derek! I don't know if the article is still > available or not. If you want to read it check Vanagon.com or email Derek > (he posts regularly to 'the list'). > > I spent A LOT of time figuring this out so I am happy to help others save > time by sharing my experience. However, I will assume that you will figure > out some of the details since it would take so long to remember and write > out. But, if you get stuck on something or just need more information, > please feel free to email me. > I checked out the current usage ( with amp meter), the force of airflow (by > wiring up with alligator clips & blowing each on my face), and the noise > factor on four fans that were readily available (I did not search far and > wide for fans). The four fans were: the stock Dometic fan, the Radio Shack > dc brushless computer fan no. 273-243B, the Fridgemate model A10-2710 Coil > Fan, and a solar powered fan that Camping World sells (the name of which I > forgot). I found the Fridgemate to provide the most air movement for the > amps and it was the quietest of all four fans. It was rather subjective, > but I felt that each of the Fridgemate fans blew between 1/3 and 1/2 the > air volume of the stock Dometic fan and used less than 1/3 the amps. I am > not familiar with the "muffin fans" that you mentioned. If I remember > correctly the Fridgemate uses about 65mA, the stock Dometic about 220mA, > and the Radio Shack computer fan about 120mA. I did not make my choice on > price. I really wanted a quiet, efficient fan system. > I visualized the airflow path (under the fridge, up the back of the fridge > through 2 sets of cooling fins, and then out from behind the fridge two > ways: out the grill behind the top of the fridge and out the grill that > adjoins the table). Feeling the heat and slow air movement at the grills, I > felt that the two air exit grills were restrictive and inadequate. So first > I enlarged the rectangular side grill hole by about two inches toward the > front of the fridge until it was flush with a horizontal board that is > beneath the stove burners. I made a new, larger grill, that was more > permeable to airflow out of flat expanded metal (1/2 inch I think). I > painted the new grill the light auto flat gray. I bought some 1/8 inch > black rubber tubing at an auto parts store, slit one wall of it lengthwise > and fitted it around the edge of the new expanded metal grill. (this keeps > grill from rattling and looks neat.) Buy taking care with where I cut the > metal I was able to use the two screws and screw covers from the stock > grill to mount the new expanded metal grill. Even without extra fans I > believe that this larger air exhaust vent would improve the cooling of the > fridge in hot weather. > The fans were placed as follows: > One fan about where the original fan was mounted (beneath the lower set of > cooling fins), but positioned better (in center, from left to right, of > fins and pointed directly through the lower fins to maximize air flow). The > second fan was mounted between the lower and upper set of cooling fins > (careful not to drill through the cooling pipe that travels from right to > left inside the fridge walls!!). Again positioned more or less in center > (from left to right) of the lower of the upper set of fins and angled to > blow air directly through fins (careful not to blow directly on thermo > switch). The third fan was mounted on the top of the fridge, immediately in > front of and blowing directly through the enlarged air exhaust vent at the > side of the fridge. (I put this one on about a 1 inch block of wood to get > it into the center of the vent hole and wired it with conveniently located > wire connectors (out of the way of the fan blades) so that it can be easily > removed when you need to take the fridge out to service it.) This > arrangement of fans spaces them out along the air flow path and each fan > adds momentum to the air at crutial points where the fins both need the > airflow and where the fins slow the air down. The third fan, on top of the > fridge, also helps to move the hot air that is generated by the propane > exhaust pipe! > Some tricks: > Because the mounts of these Fridgemate fans hold the blades out further > from the back of the fridge, I was concerned about clearance between them > and the wall of the van after installation. (It was hard to measure.) Not > to take chances, I altered the Fridgemate fans by drilling new fan motor > mount holes in the L shaped mounts such that the result would be the > Fridgemate blades would be the same distance from the back of the fridge as > the stock Dometic fan blades. I also eliminated the thermo switches on the > Fridgemate fans by cutting the white plastic tubes on which they mount to > about 1/8 inch and using shorter screws. I think I had to reverse the lower > fan on the mount to get it to position correctly in relation to the cooling > fins. The fan on top of the fridge also had to be reversed so that the fan > mount would fit between existing wire strap and the vent hole. Be careful > when reversing fans on their mounts that you wire them to blow in the right > direction!! (I wired and tested before reinstalling fridge.) > All three fans were wired to the original thermo switch after I removed and > reinstalled it with heat sink compound (from Radio Shack). I also found > that the original thermo switch mounting bracket bends easily and needed to > straighten it and take care while remounting that it fit snuggly against > the cooling fin. > I also put a very small toggle switch in the circuit for the fan at the > exhaust grill. I mounted this switch on the expanded metal grill so that I > could switch this fan off since it is closest to my ears when sitting on > the back seat. Sometimes it is nice to switch this fan off when I don't > want to hear it (the other two fans continue to work with this one switched > off). > I think that about covers the fans! Good Luck: Bill Davidson > > > > ---------- > > From: Carter <carters@thegrid.net> > > To: davidson@SIERRA.NET > > Subject: Dometic > > Date: Tuesday, August 18, 1998 7:06 AM > > > > Hello, Bill > > > > I read with interest your series of posts from 8-17-98 re the Dometic. I > > found them informative and helpful toward adding to my understanding of > both > > the theory of operation and function. Thank you. > > > > Just before you posted, I pulled mine out on Sunday for inspection and > > cleaning because I did not think that the propane mode was working. The > > stock fan worked okay, having tested it with an external battery. I also > > thought that because this thing is so hard to "observe" or check "in > place" > > that the next time I pulled it, I would figure out a way to bench test it > > which would simply require feeds for the various modes. I would also > place a > > table top fan so as to blow on the back of the unit and observe the temps > > with and without the fan. > > > > One thing we do wrong is pack the food in too tight. Hard to resist when > you > > have such a small area to begin with but we will now watch it > nevertheless. > > > > I liked what you said re additional fans because it makes sense. The more > > air transfer, the more efficient the operation, the more cooler it should > > work. Did you consider using those little muffin fans that are used for > > cooling computer chips? The reported advantage is less noise (like you, I > am > > an anti-noise freak), less amps, and the price isn't bad...around $10 > each. > > > > At this point, I am considering adding one or two fans based on your > > experience. The one behind the side vent is easy enough to figure out, > but > > if you posted further details to Roy and could relay same, I would > > appreciate it. Also I will get one of those battery operated ones for > inside > > the fridge. > > > > Thanks > > > > Kit Carter, 85 Westy GL > > Central Coast, CA > >


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