Date:         Tue, 27 Apr 1999 08:42:49 -0700
Reply-To:     Davidson <wdavidson@THEGRID.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Davidson <wdavidson@THEGRID.NET>
Subject:      Adding Dometic Fans by Bill Davidson
Content-Type: text/plain; charset="iso-8859-1"

Regarding Adding Fans to the Dometic fridge:

But first, 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! The fridges are small, but remember: The only things that
absolutely have to be refrigerated are meat and milk (though some claim
that cold beer is a necessity too!). If you need more space than a loosly
packed Dometic can provide, it is better to take along an ice chest than to
pack the food into the Dometic so tight that nothing gets cold.

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! Derek includes lots of other good
stuff besides adding fans to the Dometic. You can find his article at:
ftp://gerry.vanagon.com/pub/technical/Refrigerator-Manual.txt


And now for "Refrigerator Fan Insanity":
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