6.7 Frig Tinkering ideas? - Escape Trailer Owners Community

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Old 09-05-2014, 10:48 PM   #1
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6.7 Frig Tinkering ideas?

I'm a handy person with plenty of tools and would like ideas, successes and failures to hop up our 6.7 frig. We are planning a trip to Florida and I would like to have ice cubes in my lemonade.

Dometic suggests power level 5 above 77 degrees F. Then take out the removable freezer for additional cooling. That would leave me with no ice cubes !

Any suggestions?

Thanks, Mel
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Old 09-05-2014, 10:59 PM   #2
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Mel, have you or anyone else taken a good look at the door and how the insulation was installed. I ask because I would like to replace whatever is there with Polyisocyanurate insulation board. BTW, thanks for starting this thread.
Thx!
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Old 09-05-2014, 11:10 PM   #3
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Welcome! I have been focusing on the thermistor and have a report I'll post soon.

I would like to implement many of these concepts/products. What do you think of them?

http://www.dometicrvcentre.com.au/do...nager/item/421


From my discussions with frig specialists the priorities should be:

1. Insulation - I saw others working on it but I haven't had the chance. It is extremely critical in hot weather.

2. Flue - routing burner exhaust out of the chamber, I'm thinking "up" by sliding a tube down from the top instead of hacking the side of the trailer.

3. Flue fans - there are 3 key places and I need to send a picture of the back to a guy who will point out those 3 places. I need better pictures of the back. He said you don't have to move the air up and out as much as 'around' as the heat sets in these 3 places.

4. Thermistor to fine tune temps


5. internal fan in the box to assist natural convection down the back and up the front ... slowly.

** check all clearances around doors for air leaks, check tightness of all screws/bolts etc especially where conduction occurs. And liberally apply some good thermally conductive paste wherever appropriate.

That's my take at the moment. Please reset and/or comment.

Mel
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Old 09-05-2014, 11:25 PM   #4
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Klem, that would be my order of priority also. One more point though, remember someone mentioned that their screws were loose where the cooling fins were attached inside. That would negatively impact conduction. I would check both the freezer and refer coils and liberally apply some good thermally conductive paste.
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Old 09-05-2014, 11:42 PM   #5
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Disclaimer: please correct/comment, this is my 1st frig tinkering project.

I have included a picture of my current thermistor configuration. My goal was to pull the screw and move the whole unit so it can be placed back in the factory location IF you need to take it in for warranty service. It is simply wedged behind the drip channel end.

I found most of the screws loose through the fins. Some over 1 turn loose. You should check all the screws on both fin assemblies.

Temp remains stable at 1 power level lower (less then 40 degrees F). You can see the blue tape where I tap in to test other products/ideas.

My goal is to move the thermistor to try to find a 'sweet spot' at which it keeps it's relationship with the fins and doesn't hunt. I am searching for an adjustable thermistor.

Thermistor experiments -

I think of the thermistor as the accelerator pedal of the refer engine. It is key to fine tuning after changes to see what is the 'top end'.

The thermistor resistance rises as the box become colder. My thermistor in ice cold water read 26.4 K.

I have learned the series 8 frigs (ours 8555) have a thermistor with a different 'curve' then earlier models so thermistor kits for earlier models don't seem to work well.
Attached Images
File Type: jpg thermistor moved crop.jpg (115.2 KB, 22 views)
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Old 09-05-2014, 11:45 PM   #6
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Quote:
Originally Posted by hotfishtacos View Post
Klem, that would be my order of priority also. One more point though, remember someone mentioned that their screws were loose where the cooling fins were attached inside. That would negatively impact conduction. I would check both the freezer and refer coils and liberally apply some good thermally conductive paste.
added to the 1st message, thanks!
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Old 09-06-2014, 12:00 AM   #7
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Originally Posted by Klem View Post

I found most of the screws loose through the fins. Some over 1 turn loose. You should check all the screws on both fin assemblies.
Maybe it is supposed to be that way. Just like the aluminum siding on a house. If you screw it down tight it can't flex with changes in temperature.
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Old 09-06-2014, 12:01 AM   #8
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Kelm, I played with the thermister circuit in my 4.3 about a year ago and put a potentiometer in parallel with the one in the refer to fool it into thinking it was actually warmer than it was...don't remember the value but it was a 10 turn model, probably 500k. I didn't have any luck getting it to cool any better in spite of the resistance value. On a well cooling unit this mod may freeze your food.
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Old 09-06-2014, 12:03 AM   #9
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Maybe it is supposed to be that way. Just like the aluminum siding on a house. If you screw it down tight it can't flex with changes in temperature.
It is supposed to conduct heat from inside the box to to cooling coil behind the box. If it is loose that can happen very well.
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Old 09-06-2014, 12:07 AM   #10
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6.7 tinkering

Mel, I have spent a lot of time making small changes and then monitoring the temps with OAT of 75 to 80 as a low and 102 to 105 as a high each day. We now have cooler monsoon weather so I turned the fridge on yesterday morning (68*) with a inside temp of 70*. On electric, 5 bars, in two hours the freezer was at 22*, the fridge was 50*. No fans. This evening it was 96*, freezer 11*, fridge was at 42*. The trailer is always in the shade of a metal carport, on a concrete slab.
We'll leave on Monday for the trip from Tucson to CA, 400 miles to a point near San Diego where we will spend two nights before heading up the coast in the cooler air.
I think our fridge will be OK as we do need ice and we have frozen food and cold beer.
The mods I have done is two fans that blow up from the lower vent, 1+" of coated styrofoam panels inside the trailer skin above the lower vent that also makes a ramp to divert the fan air up over the cooling unit. The inside of the fridge and the door are covered with a double layer of the bubble wrap style of insulation. I placed the thermister out of the fins and placed it behind the insulation to keep the fan fix from blowing on the thermister. That moved the fridge temp from 55 to 35. I have 7 3/8s" holes drilled in the freezer floor, 4 are now below the fix fan others in open area.
We will now take a ice chest with us to avoid opening the door so often and probably cary two blue ice containers to trade from the freezer to the fridge.
If you happen to be at the CA rally, I will be there.
Jack
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