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Old 08-24-2019, 03:27 AM   #1
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Default Fridge cooling fan

About a year ago I built a bracket/housing that holds 2 120mm computer fans to promote airflow at the back of my absorption fridge. Seemed to work in the sense that I gained about 4-deg cooling in the fridge. But I have two issues/concerns:

1. One of the fans started making noise and died. It needs to be replaced. Okay, this was a $8 fan from Frys Electronics. Assume bearing failure. So my first question is can any of you recommend a good/quiet computer fan? Like one that you've had for several years and is still functioning. Don't need thermo control. I just switch it on/off.

2. While I'm making this replacement I'm wondering about position. My PW has an exterior vent/door at the bottom and an exterior vent at the top. The top of the fridge compartment arcs at the top to direct air to that upper vent.
Right now my fans are bracketed at the bottom pointing up at a 45-deg angle. Is it better to have the fans there or simply attached to the top vent to draw the air out? Or both?

thx.glenn
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Old 08-24-2019, 03:33 AM   #2
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About a year ago I built a bracket/housing that holds 2 120mm computer fans to promote airflow at the back of my absorption fridge. Seemed to work in the sense that I gained about 4-deg cooling in the fridge. But I have two issues/concerns:

1. One of the fans started making noise and died. It needs to be replaced. Okay, this was a $8 fan from Frys Electronics. Assume bearing failure. So my first question is can any of you recommend a good/quiet computer fan? Like one that you've had for several years and is still functioning. Don't need thermo control. I just switch it on/off.

2. While I'm making this replacement I'm wondering about position. My PW has an exterior vent/door at the bottom and an exterior vent at the top. The top of the fridge compartment arcs at the top to direct air to that upper vent.
Right now my fans are bracketed at the bottom pointing up at a 45-deg angle. Is it better to have the fans there or simply attached to the top vent to draw the air out? Or both?

thx.glenn

I think the most important thing is to make sure that the air that goes through the fan can't loop back and go through again and again. That might mean a baffle at fan level all the way across the cabinet that the fans mount to. You need to get the cool air in the bottom, over the hot places and out the the top without any side trips. You also have to deal with the heat from the boiler which you may need to separate with a baffle so it will keep it's heat off the coils. Aiming the fans right at the condenser is a good idea.
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Old 08-24-2019, 03:48 AM   #3
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Don't need thermo control. I just switch it on/off.
I would recommend that you reconsider this. A computer fan temperature controller costs like 8 bucks and (in addition to the convenience) will make your fans much quieter and they will likely also last longer, since the fans will almost always be running at a low speed.

I use one of these:

fan controller.jpg

There are many others.
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Old 08-24-2019, 05:51 AM   #4
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I would recommend that you reconsider this. A computer fan temperature controller costs like 8 bucks and (in addition to the convenience) will make your fans much quieter and they will likely also last longer, since the fans will almost always be running at a low speed.

I use one of these:

Attachment 8090

There are many others.
along that line, I bought a couple computer fans from Amazon that have a thermistor bulb attached to them that varies the speed on them.
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Old 08-24-2019, 09:34 AM   #5
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I used this fan, the same manufacturer has PWM versions.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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Old 08-24-2019, 12:22 PM   #6
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Hi: I did the same thing in my PW van a few months ago. I did not notice a significant decrease in temp. So I installed a fan inside the refrigerator. It is the one with two fans blowing directly onto the fins. This just increases the air flow inside the refrigerator. This helped a great deal. Actually kept total temp down to a reasonable level. I installed a cheap remote thermometer to keep an eye on the inside temp without having to constantly open the door.
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Old 08-24-2019, 03:27 PM   #7
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Right now my fans are bracketed at the bottom pointing up at a 45-deg angle. Is it better to have the fans there or simply attached to the top vent to draw the air out? Or both?

thx.glenn
Glenn,
I have found attaching the fan to the top vent better. I previously had a fan in the center and I think it looped much of the air around inside the vent cavity. After reading about this setup:

https://www.arprv.com/rv-fridge-slide-out.php

I got a fan like the one they sell and put it in the top vent. That has worked much better for me.

I also have done several other mods, with the cumulative effect that the fridge works much better. In very hot weather it is borderline, so I move some frozen ice packs that I keep in the freezer to the fridge part.

http://www.classbforum.com/forums/f8...ance-8484.html
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Old 08-24-2019, 04:17 PM   #8
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Hi: Agreed. In hot weather not much works. One needs to do as much as possible. There is another consideration. Make a shade cover for the outside of van. To increase or create shade for vent areas of the van so it remains cooler. I have not done this yet. I believe it will aid.
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Old 08-24-2019, 04:47 PM   #9
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Hi: Agreed. In hot weather not much works. One needs to do as much as possible. There is another consideration. Make a shade cover for the outside of van. To increase or create shade for vent areas of the van so it remains cooler. I have not done this yet. I believe it will aid.
I used to have fridge temp in the mid 40s, even higher if in high 90s outside. Now temps are in 36-39 in hot temp and hit 40 in the 90s. So the mods have worked very well.

Covering all the exhaust openings except for the fan exhausting the top vent has made a huge difference when driving. On 12v it holds the temp pretty good. Before the mods when driving the fridge temps always went up. I believe the airstream over the vents prevented good airflow in the bottom and out the top vent.

A shade cover on the fridge side of the van should help. I made one but have not tried it yet because I haven't needed it.
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Old 08-24-2019, 07:39 PM   #10
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I used to have fridge temp in the mid 40s, even higher if in high 90s outside. Now temps are in 36-39 in hot temp and hit 40 in the 90s. So the mods have worked very well.

Covering all the exhaust openings except for the fan exhausting the top vent has made a huge difference when driving. On 12v it holds the temp pretty good. Before the mods when driving the fridge temps always went up. I believe the airstream over the vents prevented good airflow in the bottom and out the top vent.

A shade cover on the fridge side of the van should help. I made one but have not tried it yet because I haven't needed it.

I had a Dometic absorption fridge that worked fine when stationary but began to increased in temperature when driving after it was 2 or 3 years old. The longer the drive, the higher the temperature increased. Added a bigger cooling fan on condenser, increased insulation around fridge, closed off condensate drain in fridge but nothing helped while driving but it continued to work fine while stationary. Finally in desperation after this continued for almost 2 years, I used cord caulk around the interior cooling fins in the freezer and fridge and that fixed the problem while driving. Apparently the high air velocity when driving was able to penetrate through the back side of the fridge and leak warmer air into the interior of the fridge causing the temperature to increase. Not sure why this happened after owing the fridge for 3 years but maybe the urethane foam used to seal the exterior of the fridge contracts with age or maybe just cracks from vibration. It does not take much outside air to raise the temperature of an absorption fridge and it cannot keep up with continuous leaks even if small.
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Old 08-25-2019, 04:59 AM   #11
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Great responses; great links peteco and bud. So I need a bit of clarification on the workings of the fridge. The boiler sits at the bottom and is the large round container out of which the smaller tubes go up and form the coils on the back. Is this right? If so, some of you mentioned a baffle to separate the boiler from the upper coils. Are you suggesting a horizontal piece of say galvanized that would fit in slightly above the boiler and perhaps angle down so that the cool air coming in would be directed to the upper coils? Is it that you want to cool the coils but you want the boiler to remain hot?
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Old 08-25-2019, 01:37 PM   #12
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Great responses; great links peteco and bud. So I need a bit of clarification on the workings of the fridge. The boiler sits at the bottom and is the large round container out of which the smaller tubes go up and form the coils on the back. Is this right? If so, some of you mentioned a baffle to separate the boiler from the upper coils. Are you suggesting a horizontal piece of say galvanized that would fit in slightly above the boiler and perhaps angle down so that the cool air coming in would be directed to the upper coils? Is it that you want to cool the coils but you want the boiler to remain hot?



If I understand the question correctly, any baffle for the boiler would go vertically from the bottom to the top, so it basically has it's own chimney. You want to keep the boiler heat away from the rest of the pieces if possible.



The horizontally mounted baffles mentioned would be for the rest of the area around the condenser and would go from one side over to the vertical baffle for the boiler. The horizontal baffle is to keep the air in that side from being able to loop back to the inlet air and not go out the top by directing the air to where needed and reducing the area it has to loop. This makes for better flow from inlet to outlet.
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Old 08-25-2019, 02:12 PM   #13
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I have a 40 ft. 5th wheel trailer that has a 13 cu. ft., Dometic, 4-door refrigerator. The factory installed 4 pancake fans just above the top coil. They also installed a vertical panel near the coil in order to direct all the airflow through the coil. Recently, 3 of the fans failed and the refrigerator temperature wouldn't go below 45F. I replaced the fans and all was well again. The fans are controlled by a snap switch thermostat attached to the top coil.

I think the bottom line is the fans should be above the top coil and a baffle needs to be installed to force the cooling air to flow through the coil and not around it.
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Old 08-25-2019, 06:55 PM   #14
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Originally Posted by GallenH View Post
The boiler sits at the bottom and is the large round container out of which the smaller tubes go up and form the coils on the back. Is this right? If so, some of you mentioned a baffle to separate the boiler from the upper coils. Are you suggesting a horizontal piece of say galvanized that would fit in slightly above the boiler and perhaps angle down so that the cool air coming in would be directed to the upper coils? Is it that you want to cool the coils but you want the boiler to remain hot?
Watch the video at the top of this link. It does a good job of describing the components and operation.I think what you are describing is called the holding tank in the video.

https://www.arprv.com/how-dometic-no...idge-works.php
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Old 08-25-2019, 07:28 PM   #15
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Thanks booster and peteco. So I'm going to try to attach an image of the back of my fridge:
fridge.jpg
Hopefully that worked. The LP burner is at (1) The burner tube has an insulated chimney (2) which vents at (3). When you say a vertical baffle are talking something like where I've drawn the red line up from the chimney? Something that would keep the burner heat going up past the back of the fridge. My fans were originally installed at ******** pointing at about 45-deg. I'm now thinking about putting them on the upper vent as exhaust fans.

Thanks.
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Old 08-25-2019, 09:05 PM   #16
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Thanks booster and peteco. So I'm going to try to attach an image of the back of my fridge:
Attachment 8094
Hopefully that worked. The LP burner is at (1) The burner tube has an insulated chimney (2) which vents at (3). When you say a vertical baffle are talking something like where I've drawn the red line up from the chimney? Something that would keep the burner heat going up past the back of the fridge. My fans were originally installed at ******** pointing at about 45-deg. I'm now thinking about putting them on the upper vent as exhaust fans.

Thanks.

Thanks for the info Gallen. Good to see what you have.


The goal with the vertical baffle is to keep the boiler heat from going over the coils, so it might be better to put it a bit further left and all the way to the floor of the cabinet, as long as there is still vent available there so air can get to the burner.


Personally, I like the location of your fans as they concentrate the air right on the coils, which is good. What may not be all that good is where the fans are picking up the air they blow. If it is coming across from the burner or other hot area that robs it's cooling capacity. Even more likely is that the air is blown up with the fans but then makes a big loop back down into the fan inlets. That is where the horizontal baffle that was mentioned earlier comes in. Basically it divides the cabinet horizontally right at the fans so only cool air from the vents goes to the fan inlets. The baffle also prevents any air from going out anyplace but the upper vents.
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Old 08-29-2019, 05:55 PM   #17
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This isn't responsive to the OP but may be helpful for others following this thread, I've had good luck with this 2 piece interior fan on eBay. Installed about 2 years ago.
<https://www.ebay.com/itm/391282772544>

Figure out how you're going to wire it before ordering.
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Old 08-29-2019, 06:23 PM   #18
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Default Fan Fix

When I worked for United airlines, (ages ago) on their computer systems, many of their 4Ē computer micro-fans failed. I would remove the fan, pop off the cover over the bearing on the rear of the fan, and oil that bearing with 10-weight synthetic oil. Then pop on the cover again. I almost never had to oil the front bearing. Those fans always would always then work. Iíve got two of these repaired fans in my work shed now that Iíve been running off and on successfully for almost 50 years now. This repair does work.
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Old 08-29-2019, 07:09 PM   #19
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The important points are to prevent recirculation of hot air, direct all the air over the finned coil(s) at the top, and increase the amount of air passing over the coils.

In the picture you can see I mounted five computer fans on our RT's lower fridge panel. (The fans are bolted to aluminum bars and the bars are bolted to the panel.) The fans are mounted over the bottom opening in the panel. I sealed the two other openings in the panel with aluminum duct tape. Small gaps around the fans are also taped over. I did this about 12 years ago and the fans are still running great, albeit with a bit of noise now. The fans are controlled by a switch inside the van. A thermostatic switch is interesting, but I think unnecessary.

Our RT has a similar panel at the top of the fridge compartment. The finned coil sits just below the top opening the panel. I sealed the two lower openings with duct tape. Thus all of the cooling air is forced over the finned coil.

This bodge works stupendously well, if I say so myself. The fridge stays cold running on DC when we drive and it chills down quickly when we start it even in 90-100 degree weather. When we park we can leave the fridge running on DC for an hour or two with no worries (we have a 200 Ah battery).

I tested the fridge in 80-85 degree weather. The duty cycle (fraction of time the heater is on) running on AC changed from 76% w/o fans to 61% with the fans on. On DC the change was from 100% to 72%. The fridge held about 35 degrees throughout all the runs except for DC w/o fans when the fridge crept up to 38 degrees. If the weather had been much warmer, on DC the fridge would not have stayed safely cold.

The fans draw 350 mA. In my DC tests, the fridge used 4.2 Ah per hour less electricity, for a net saving of about 3.8 Ah/h. The energy saving is nice, but the really important result is the fridge always stays cold.

I have not thought of a way to observe the gas burner's duty cycle, so I don't know how much the fans improve performance on gas. I suspect it must be similar because the results show the problem with Roadtrek's installation is inadequate cooling air draft.

Some air blows through the boiler, but even so this arrangement is effective enough for me. I don't think going to the trouble of isolating the boiler from the cooling air is worthwhile. I also worry that when running on gas, if the hot exhaust were not mixed with cooler air, it might melt the plastic panel.
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Old 08-31-2019, 05:16 AM   #20
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SteveJ points out the benefit of temp control. I used one and also installed a switch that allows me to have it always on if needed, or to turn it on/off if the thermostatic switch fails. I bought a switch that actually has adjustable trip points. I also added the baffle to direct air up and through the fins. I used a pair of computer fans mounted directly to the upper grille, used the lowest amperage fans I could find. Having the baffle allows for lower load fans. Note that I installed a disconnect plug in the power line to allow removal of the grille when needed for maintenance.

Another smart add is a wireless thermometer for the fridge and freezer so you can know what's going on before you open and find spoiled food.

The whole project cots $36 in parts for the fans/cooling and $20 for the wireless thermometers.
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File Type: jpg 0425191008.jpg (513.8 KB, 9 views)
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File Type: jpg 0425191709.jpg (98.6 KB, 8 views)
File Type: jpg 0426191344.jpg (267.3 KB, 10 views)
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File Type: pdf RV Fridge Auxiliary Fan.pdf (966.0 KB, 11 views)
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