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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.
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File Type: jpg thermistor moved crop.jpg (115.2 KB, 24 views)
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Old 09-05-2014, 11:45 PM   #6
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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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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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Old 09-06-2014, 12:12 AM   #11
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Well, let's do a survey. How many people find the screws are one turn loose and how many find that they are tight? We might find that they are all loose, which may indicate a reason for being one turn loose.
In the meantime, I'm going to try to figure out why my 5 cu. ft. fridge, which has been turned on elec. for two days is suddenly as warm as the inside of the trailer ( even though the food inside feels cold ). It could be that my wife didn't properly close it while loading it, or it could be that the indoor/outdoor thermometer I'm using has gone goofy.
I switched it over to propane, just to confuse matters even further. Within 20 minutes the thermometer indicates 35 degrees.
I'll just have to finish this six-pack and check again later.
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Old 09-06-2014, 07:23 AM   #12
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I removed our fins to get access to the hole for the thermistor wire (6.7). Our screws were all loose as well. With all the sticky thermally conducting grease between the tubes and backside of the fin assembly, I don't know how much difference it would make to tighten them. I'm beginning to think they were intentionally installed that way OR the grease squeezed out over time resulting in the screws effectively loosening. There are probably one or two people at the Dometic factory who would really know the answer. So I snuggedbour up but wouldn't call them tight.
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Old 09-06-2014, 11:10 AM   #13
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6.7 tinkering

Next morning at 6 a.m. went out to wash the trailer, 74* oat and 78* inside. Freezer 0*, fridge is 32*. I opened the door a couple of times to check mechanical gauge against the remote and the second time at 7:30, still 0 and 32 with out side temp up to 78*
I checked the screws and they varied, mostly tight with one a single turn and a couple a half turn to snug them up.
Checking for leaks at the door a week or so ago, fridge was 30+, trailer 78* and using a IR temp unit there was a consistent 72* at the door seal.
Jack

Hoping for good weather next week on the West coast, but we do need rain.
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Old 09-06-2014, 01:08 PM   #14
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Hi Parker,
As for tightening I found this:

New Page 1

You must apply thermal mastic to the coils of the cooling unit that contact the aluminum fins of the refrigerator. After the mastic has been applied, install the aluminum fins to the cooling unit. Be sure to well tighten the screws that mount the fins. There are brackets for the screws below the surface of the foam. You should see the screws slightly pull the area around them inward. Getting the fins on tight with mastic is critical. Failure to do so will cause cooling problems in the lower box. You should also put mastic on the freezer coils, before installing the freezer plate later. The next step is to apply about a half inch bead of sealer "Silicone or Latex Caulk" around the edge of the foam block and place the cooling unit into the refrigerator.
------------

My guess is they are loose from the compound being squeezed after install and the thermal movement.

On telecommunications equipment we torqued the bolts, I never saw the sheet metal type screws on the series 8 units so I wouldn't want to guess. I tightened them 'firmly' ...
Mel
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Old 09-06-2014, 01:20 PM   #15
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Interesting perspectives!

The Golden Path To Refrigerator Happiness

Vanagon

There will be a tinkererer quiz on Monday : )
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Old 09-06-2014, 02:31 PM   #16
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Hi Parker,
As for tightening I found this:

New Page 1


Mel
Thanks, Mel. Good read!
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Old 09-06-2014, 02:54 PM   #17
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AES - tricking it to only use propane -

I disconnected the red 12vdc (wire nut big and small wire together that was on the heater + lug) from the heater element AND unplugged the AC power cord.

That forces AES to go directly to propane. I've read the AES can get flakey so this insures I am running 100% propane for testing.

Good way to troubleshoot AES too, by forcing in a mode.
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Old 09-06-2014, 03:14 PM   #18
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AES - tricking it to only use propane -

I disconnected the red 12vdc (wire nut big and small wire together that was on the heater + lug) from the heater element AND unplugged the AC power cord.

That forces AES to go directly to propane. I've read the AES can get flakey so this insures I am running 100% propane for testing.

Good way to troubleshoot AES too, by forcing in a mode.
Is there an advantage to doing it this way as opposed to setting the mode to "gas"?
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Old 09-06-2014, 03:59 PM   #19
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In the meantime, I'm going to try to figure out why my 5 cu. ft. fridge, which has been turned on elec. for two days is suddenly as warm as the inside of the trailer ( even though the food inside feels cold ). It could be that my wife didn't properly close it while loading it, or it could be that the indoor/outdoor thermometer I'm using has gone goofy.
I switched it over to propane, just to confuse matters even further. Within 20 minutes the thermometer indicates 35 degrees.
I'll just have to finish this six-pack and check again later.
Glen, I have found on the 5 cu ft fridge that the switch that controls the mode (electric, gas or off) is finicky. In our case we thought the fridge was off but was still operating in the 110V mode. These fridges don't have an indicator light to tell you if the fridge is in fact on.
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Old 09-06-2014, 04:10 PM   #20
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Glen, no matter what you find out, do what any self respecting man would do...blame your wife.
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