Dometic 182B fridge cold plate R&R

[SSWesty]

I am doing a little tune up on my fridge and noticed my cold plate has about a 10 degree difference between the left and right sides. This is after being on for about 18 hours on propane. I've captured the temps with an IR thermometer. The cold plate is secure however I was expecting the cold plate to be more even in temperature.

First question is this normal? I know folks have removed cold plates and attached them with new thermal paste however I have not seen if that improves anything.

If I do decide to remove the cold plate are there any tricks to getting it to separate without busting everything up?

[Vanagon Nut]

That part should pull free from the cold tube. The cold tube gets cooler near LH end. Note how the narrow flexible metal tube fits in the cooling unit. There should be a small white rubber or silicone piece holding that tube in a groove on cooling unit. If you search domestic posts under my handle, you should find a link to a bunch of pics of my dometics.

When reinstalling that cooling unit, you might want to refresh the green paste with computer cou paste. A little goes a long way. The idea is to fill any gaps between tube and cooling unit.
Be careful not to push fit cooling unit too far to left over lip at end of cold tube. Doing so would distort the part at that end and would create a large gap between the cooling unit and pipe.


Neil
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[DLJ]

VanagonNut,s advise is sound. What is your overall temp? If your around 35 to 45 degree's below ambient temp. your OK.

[SSWesty]

Getting ready to remove the cooling unit. Thanks for the tip about the small tube underneath the cooling unit, I'll be cautious with that sucker. My temps were about 30 degrees below ambient so we'll see if I can get it to do better. I'll fire it up with the cooling unit off to see what the temps look like on that cooling tube. It would be great if that whole tube would cool down rather than just the left hand side.

[Vanagon Nut]

That thin tube isn't too fragile. I was suggesting being careful to note its position more than anything. It basically slips in the groove and is held in place by that white bit. My guess is that it should contact the coolong plate to some degree. Pun intended.

Just brace your knuckles against the fridge back and pull forward at bottom and top of cooling unit with fingers.

AC mode should provide a good point of reference in terms of how well the fridge cools. In a perfect world, the only real difference in terms of performance in each mode is the lack of thermostat while in DC mode.

A significant difference in temp between end of pipe and point at bend might indicate a less than efficient fridge. I'm really not sure about that. It's normal for end to be colder.

Amount of differential to ambient is not a hard number. Eg if it's 90 F ambient you may not pull even a 30 F diff. And, differential also depends on how much already cool stuff is in the fridge. Ie heating up an empty fridge takes more power. For lack of better expression.

Neil.
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[SSWesty]

Making progress. Cold plate is off and I noticed that there seemed to be a liberal amount of thermal paste used on mine. Contact looked good except for two spots on either end. I question if there was too much paste and if that was impacting performance.

The cold plate mates to the cooling tube via a half-round channel. The half-round channel is riveted to the fins on the cold plate. On the right-hand side of the cold plate there is a slight gap between the rivets where the half-round channel meets the cold plate fins. I was able to slide a feeler gap in there about a 1/2" before hitting thermal paste. If my rivet gun will fit in where it needs to I'll remove the rivets and re-bed the right-hand side.

I fired up the fridge on propane to see what happens to the cooling tube. After about 90 minutes it gets pretty cold and the frost has been moving across the tube left to right. I left the fridge door open for this test and at the moment the back end of the rig is up on blocks. So the fridge is not level and the back wheels are about 4-5inches higher than the front.

Based on what I am seeing with the temperature differences I would think it would be better to have nothing but fins on the left side and skip the ice cube tray shelves. I have made ice cubes with the fridge to see if it would do it however I just use the trays now to store food I want to keep close to frozen like chicken breasts. It seems like having fins on the left side would be better overall at cooling than the ice cube tray shelves. Also that seems like the best place for an interior fan. Heck I even wonder about skipping the cold plate and just mounting a fan to blow down that tube.

Thermal paste is something new to me so here is what I think would work http://www.frys.com/product/8454178?site=sr:SEARCH:MAIN_RSLT_PG Any feedback on that stuff. Also it calcs out to about 15 square inches of surface are that needs to be covered.

[Vanagon Nut]

Might provide one reference point?

Can't recall which fridge but these are from mine.
probably my 182A from my '81. The cooling fins were screwed on.
My 182B had rivets on those parts.

Neil.

_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[SSWesty]

It looks like my fridge had more goop on the cold plate than what VanagonNut shared. It almost looks like there where numerous spaces with no goop. This thermal paste stuff is all new to me so I am not sure if more or less of the factory stuff is better or worse.

I had a computer fan handy so I tried just letting it blow on the cooling tube. After about an hour it knocked the frost off that can be seen in the prior picture except for the end. The 4" fan definitely helped cool the fridge down however a smaller fan blowing down the tube lengthwise would probably be a better arrangement. Interesting idea that I think may work better than the cold plate itself with a little fine tuning. I am headed to Yellowstone and the Tetons on Saturday so no more time for experiments:-)

I reattached the cold plate to the cooling tube with Arctic Silver 5 from Frys Electronics. It was $20 for 12 grams and seemed to have more metal in it than other offerings. My electrical engineer buddy said metal is good for heat transfer. Not all thermal paste is rated for colder temps and only go down to 50 degrees. Arctic Silver is rated below zero so I felt good about that. 12 grams seemed like the right amount of paste for the job. I put 4 stripes of paste on the cold plate and 1 zig-zag stripe on the cold tube. The factory goop was probably 1/16" of an inch thick and this stuff probably spread out to be more like 1/32" thick or less. It seems like this product should do better than the factory goop. Time will tell. To help bed the cold plate on the cold tube I rotated the cold plate back and forth about an 1/8 of a turn to help it spread out the paste. I also used a heat gun and warmed the cold plate up to about 115 degrees to help soften the paste which I think helped bed it securely. I plan to do a couple more heat cycles with the heat gun before I turn the fridge on. The product says it can take up to 200 hours to cure. In a couple days I'll let you guys know if the cold plate falls off once I fire up the fridge:-)

[jmranger]

Bump... SSWesty, any update? How does it perform with the R&R completed? Is the paste able to hold the plate in place?

[Vanagon Nut]

I now wonder if the "Bb" (musicians term meaning "average" ) CPU paste I used was a lot worse at conducting than the Arctic Silver SSwesty used.

I bet the screws or rivets mishape the pieces during assembly hence the need for paste.

What about lapping mating surface of each piece on a piece of glass?
Use valve lapping compound? Give your food that nice "mechanical" smell.

Neil.
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[SSWesty]

I started this project 1 week before heading out on a trip to Yellowstone and it went sideways. A couple life events also popped up so I was in scramble mode to stabilize the frig for the trip. First the Arctic Silver thermal paste didn’t work out then the frig “popped” once when I was lighting it on propane and it became difficult to keep running after that. So I got down to about a 24 hour window to resolve the issues and get out of town. I pulled the frig and cleaned up the burner box which corrected the issue with not wanting to run well. Since I had it out I adjusted the 3 speed computer fan from low speed to the medium speed setting. I put this fan in about 6 years ago to replace the noisy factory fan. On the low speed setting it would run for hours when it got warm and now on the medium setting it will cycle on for about a minute then shut off for a while depending on the temps in the van. After the Yellowstone trip I think my ideal setup is to add a switch so I can turn the fan off when the frig is not in use then add another to toggle between the medium and high speed fan settings. Seems like I could use the high speed setting when it’s above 85 degrees outside.

As for the cold plate I couldn’t get cold temps on the left hand side so I knew something was up. I pulled the cold plate and saw the paste didn’t spread out on the cold end.(The frig was upside down when I took this picture so when you look at it the right side is the cold side and is on the left when it’s installed.) You can see the beads of Arctic Silver did not spread and flatten out. So I had air gaps stealing away the cold. I think my cold plate or cold tube in the frig may be slightly warped. When I pull it again I need to get a straight edge in there to figure out if something is off. I am not sure if the Arctic Silver is thin enough to work in this application. I rotated the cold plate back and forth on install to try to spread the paste around but you can see in the picture that it didn’t happen on the cold end. I also applied heat during the install and that didn’t seem to end up doing anything good and may have messed up the factory paste on the cold plate where the semi-circle mount mates to the heat sinks.

Plan B was to abandon the Arctic Silver and switch to Super Lube Silicone Heat Sink Compound. It was all I could quickly find in stock that wasn’t a small quantity of 5 or 12 grams. Luckily Grainger came to the rescue with some if stock, you can also order it through Home Depot. This is stuff spreads much better than the Arctic Silver. Below is the coverage I went with for the trip.

This performed much better than my first attempt with the Arctic Silver however I think I can do better. The temps on the left side were not even and the ice cube trays seemed to be about 5 degrees warmer than the fins on the heat sink below them. After measuring the consistency of the temps the left side is always about 10-15 degrees colder than the right side. I want to switch the heat sink from the right side to the left. Like JMRanger I think it would be best to abandon the ice cube tray for 2 right side heat sinks. The left 6-8inches of the cold tube seems to do the heavy lifting with cooling. The second change would be to add an interior fan on the left side since that is the coldest side. Now that I understand this thermal paste better I’ll try to figure out how to get it down to a minimal amount of paste between the contact surfaces. My next window to fiddle with it is in mid-August so I am keen to see if others gain some insights on improvements.

[Vanagon Nut]

I might be seeing things but is the end the 1/2 moon on the plate splayed out at one end?

It's possible to install the plate (incorrectly) so one end of the 1/2 moon gets pushed over the lip at end of cold tube. Doing so would create the gap between 1/2 moon and tube you're seeing.

Neil.

_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[SSWesty]

Good eye Neil, I'll need to check that. I didn't notice anything when it was apart but I was working quickly. Might be the wide angle lens my cell phone but I'll measure it when I pull it next. That would not be helpful if it was creating a gap.

[jmranger]

Thanks for the update. Given that it doesn't seem to be a straightforward upgrade and that the performance of mine is satisfactory as-is, I'll probably focus on other issues for now.

The (non-)spreading pattern of your first attempt is indeed strange. Any flex issue? Would it be worth doing the installation with the fridge on its back, with shims between the cold tube and the wall? Add zip ties to prevent the paste from developing cracks when cured?

Good luck, and keep us posted.

[puchfinnland]

I am following up on this post because I followed thru on the modification of installing the second full size heatsink from another fridge.
(note on thermal paste- I scraped off the original paste and thinned it with a few drops of denatured alcohol and reapplied heatsink, only as this is a test.)
If you want to copy this and can not source a used westy heatsink just purchase new heatsinks from ebay and replace all original heatsinks
ebay "100x69x36mm Aluminum Heatsink"


I am also considering to add more heatsinks on the backside, from
ebay - "heatsink 60x150x25mm" these can be cut and added.

my findings

original fridge setup- ambient temp 60
inside of box temp 38
with modified heat sink ambient 60
inside of box 37

I then put in a second original cooling fan wired to 12v temporarily inside, directed at the left side (coldest side)

inside temp went down to 34.5-35,
after 12 hours the inside temp was 31 ! I turned the thermostat back as it was now too cold in the box.

[puchfinnland]

Step 2 was to make a proper fan to blow air down the modified cold plate.

I made it from a 18" piece of downspout from Home Depot, it is carefully cut so air only blows on the top of the fins and not behind the cold plate,
Fans are 40mm easily obtained from ebay,

[jmranger]

Nice work. Thanks for trying it and reporting back.

[puchfinnland]

my findings are even without the inside fan on, with the extra heatsink the fridge pulled to almost freezing temp.
this was with ambient temp of about 60 degrees on 120v
with a fan on it would freeze water sitting on bottom of fridge.

Testing is still going on.

[Vanagon Nut]

puchfinnland

Thats really a neat idea. Thanks for posting about what you did and found for temps.

One thing I noticed on one of my 182's was that ice tended not to form on portion of cold plate below the small cpu fan I installed. I wonder if, and how, fan speed (how fast air is moved) relates to efficiency of the cold plate(s)?

Neil.
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[crazyvwvanman]

It seems the left end is the colder end on mine.

Mark