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
Content-Type: text/plain; charset=ISO-8859-1
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> 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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