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Old 06-02-2009, 09:14 PM   #1
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Retrofitting a Isotherm refrigerator

I just finished up replacing our original 4 CF Norcold refrigerator with a new 4.6 CF Isotherm Cruise 130 refrigerator. Friend/forum member Charlie had one of these refrigerators installed with his build and was happy with it except for a couple of reservations. We were interested in replacing our Norcold refrigerator since it appeared to be draining the house battery much more now than when it was originally installed, possibly because of a decrease in efficiency due to age. Note that these Isotherm units are not cheap...ours cost about $1500.

The concept for the refrigerator is very beneficial for SMB owners if you chose the ASU (Automatic Start Up) option ...the refrigerator reads the voltage of the supply (whether the house battery, shore power, or solar) and basically adjusts the cooling cycles in response to the available voltage level to minimize battery usage. In addition, the design includes what the manufacturer terms a "holding plate" directly under the freezer compartment. This "plate" appears to be a gel-filled plastic "slab" similar to the the reusable freezer gel packs that are frozen and used in ice chests. When there is a good supply of electricity, the unit freezes the "holding plate" and then allows it to cool the refrigerator when it is running on only the house battery. I should mention that the unit is VERY quiet. The fan can't be heard at all and the compressor noise disappeared once I had the unit slid into the cabinet.

I initially tried to purchase one of these units from an on-line dealer but was told that I couldn't since there was a distributor here in the Bay Area. Fortunately, we purchased ours from that distributor (Svendsen's Boat Yard in Alameda, CA). A week or so after picking up the unit, I decided to power it up before going further with the installation and immediately noticed that the cooling fan blade appeared to be hitting a strut or something. I called my contact at Svendsen's and she suggested contacting Isotherm directly. Long story short, I received a replacement fan a week later but when I applied power to it, it didn't work at all! Looking at it more closely, I realized that they sent me a fan which had been pulled out of a used refrigerator! Not only was there greasy dust on the inside of the fan housing but one of the struts was broken! I called my contact at Svendsen's and expressed my outrage! She e-mailed Isotherm and I got a call the following morning from Isotherm along with an apology and a new fan via overnight UPS.

The installation wasn't difficult but I wanted to address some of the problems Charlie told us about. In addition, the new refrigerator, while the same capacity as our old unit, is smaller in all dimensions than the old Norcold unit.

I ordered the Isotherm 3-sided mounting flange. It appeared that the flange was to be installed by attaching it the refrigerator by screwing it to the sides of the refrigerator and lining it up with a metal piece on the sides of the refrigerator. But mounting it in that location seemed to make it interfere with the opening of the door and I therefore installed it a measured distance (16.5") from the rear of the unit. That mean drilling new clearance holes for the screws so that they would still screw into this metal piece.

With the flange installed, the width of the unit was about a 1/4" narrower on each side of the opening provided by SMB for the Norcold unit.That meant that the factory-provided screw holes in the flange wouldn't work. Rather than rebuild the cabinet, I screwed pieces of 1" square poplar wood (which I found at our hardware store) along each side of the opening:



The Isotherm unit was also shorter than the old Norcold unit. To compensate, I screwed spacers to the floor so that the unit was tight to underside of the cabinet:



This was a frustrating exercise because of the carpeting under the unit...my ultimate solution was to first screw two spacers to the floor and then measure the height needed for a second set of spacers. That will allow you to screw the first set down tight on the carpeting...otherwise it will be impossible to determine the proper spacer height to result in a nice fit.

The next issue to be addressed was electrical contact...as supplied by the factory, the unit uses slip-on connectors for the power supply and other wiring to the ACU module. This module uses the same type connectors to plug it into the main control module behind it. Charlie first discovered that the wiring connections to the ACU module tended to shake loose over time. His solution was to remove the connectors and solder the wires directly to the circuit board terminals...I did the same thing. The ACU comes apart via the obvious screws on the case and soldering the wires to the terminals is not difficult if you know how to solder.

Making sure that the ACU doesn't come apart from the main control module is more difficult. Isotherm told Charlie to use wire ties to hold them together and told me the same thing. But Charlie has discovered that this solution doesn't work over time. Charlie told me that, once his warranty expires he plans to solder these connections too. But I don't want connection failures while waiting for the warranty to expire. After giving it a lot of thought and making a lot of sketches of possible approaches, I came up with the idea of using pieces of aluminum angle and threaded rod to hold the main control module and ACU unit together. Here are the bottom angles I made:



Basically, there are angles which fit on all four edges of the combined unit...front top and bottom, back top and bottom. The design concept is that horizontal rods keep the two electrical modules together and prevent them from coming apart while the vertical rods keep the pieces of angles from slipping up or down and compromising the holding power of the horizontal rods. The rods are 6-32 brass all-thread while the angles are 1/2" aluminum. The front angles have cut-outs for the telephone-type connections incorporated into the ACU control panel. There are four horizontal and four vertical threaded rods which hold the two units together...I used nuts with nylon inserts on the rear and bottom pieces and double nuts with lock washers on the other locations so that the framework holds everything together without putting undue pressure on the plastic cases themselves.

Since you need to be able to slide the rear bottom angle into place and then add the vertical rods, I tapped the holes for the vertical rods on the rear bottom angle so that the brass threaded rods could be screwed into place during assembly. While "designing" the parts took a while and assembly required some ingenuity, it appears that it will solve the problem:



Note that I didn't realize until I was hooking up the wiring that I reversed the color of the wiring for the fan at the bottom of the red ACU module...I fixed that when I connected the wiring to the fan itself. You can also see in this photo how the wiring was soldered to the ACU module and then protected with shrink wrap.

Charlie incorporated a terminal block into his wiring so that the ACU module could be removed without the need for cutting wires. I thought about this approach but decided that I could deal with such problems by just cutting wires (I obviously have a lot of confidence in my design). I used butt connectors for the main power leads with "suitcase" connectors for the power to the blue wires. I used wire nuts for the fan power connections.

The ACU control panel connects to the ACU module via a telephone-type cable. I mounted the control panel above the narrow shelf provided with the EB-50 design since Charlie mentioned that you wanted the panel where you can see it and make sure that nothing was going wrong:



The thermometer next to the control panel monitors (via wireless transmission) the temperature in the refrigerator and also shows the temperature inside the van. (I have another sender unit to give me the outside temperature while camping.)

Charlies also suggests that a switch be included in the power supply to the Isotherm refrigerator in order to "reboot" it if needed. I used some 120v surface components from the hardware store and a switch mounted on the outside wall behind the driver's seat for this purpose.

Here is the installed refrigerator:



Since the factory-supplied holes in the flange were too close to the outside edge of the flange itself, I drilled new holes to line up with the 1" square side wood spacers. I went ahead and ran screws into the factory-supplied holes just to cover them up.

Besides being a long post, this was a drawn-out project due primarily to the fan issue...I also probably spent a number of hours devising a solution to holding the ACU module tight to the main control module. Recognize that, as an engineer, I tend to be a "suspenders and belt" type of designer...we are taught to include significant safety factors into our designs and that manifests itself into my concept that, if 4 screws seems fine, 5 or 6 would probably be better. There are most likely simpler designs which would solve the problem of holding the units together.

I am very hopeful that the expense of this new refrigerator will "pay" for itself with significantly less power consumption. When our van was new, we could camp for several days without starting up the van, even without solar. But as I related in a long post a month or so ago regarding our house battery draw-downs every night, I think that our old refrigerator was getting too old and causing us problems. We haven't been able to get out much recently for a variety of reasons but I'll report in the next couple of months on whether this replacement refrigerator helps as much as we hope.

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Old 06-04-2009, 08:51 AM   #2
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Re: Retrofitting a Isotherm refrigerator

Great write up. In my 05 the carpet doesn't go beneath the fridge and the counter top is the same formed top as the sink area, although with the smaller dimensions probably wouldn't be a problem. Anybody want to buy a slightly used Norcold for $1500?
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Old 06-04-2009, 10:58 PM   #3
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Re: Retrofitting a Isotherm refrigerator

Nice install Jack. Can you recharge the refrigerant in this model you installed? I seem to remember some talk about the isotherm being able to be recharged.
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Old 06-05-2009, 06:58 AM   #4
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Re: Retrofitting a Isotherm refrigerator

It appears that you can recharge it. In the trouble-shooting section of the instructions, it talks about possible causes if the compressor is running but no refrigeration is generated and suggests the cause might be the loss of refrigerant. The Action is to do leak tests, repair possible leaks, etc. and then evacuate and refill the refrigerant.
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Old 06-05-2009, 07:23 AM   #5
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Re: Retrofitting a Isotherm refrigerator

Excellent write up. I'm sorry I ever saw Charlie's refrig in Death Valley a year ago, since I have lusted after one ever since.

Jack, you should open up an SMB refrig installation shop. I will be your first customer!
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Old 06-05-2009, 10:29 AM   #6
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Re: Retrofitting a Isotherm refrigerator

I work too slowly that, either I'd never make a profit, or no one could afford to hire me!
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Old 06-06-2009, 05:58 AM   #7
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Re: Retrofitting a Isotherm refrigerator

Jack said:
Quote:
I work too slowly that, either I'd never make a profit, or no one could afford to hire me!
That never stopped Chrysler or GM. No wait....
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Old 06-22-2009, 09:50 AM   #8
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Re: Retrofitting a Isotherm refrigerator

We finally got time to take a short trip to Mendocino last week and check out the performance of our new Isotherm refrigerator. Here is my report as promised...

After completing the installation, I of course hooked up to shore power and turned on the refrigerator for a couple of days while parked in the driveway. At first, I was concerned because it didn't seem to get cold enough and seemed to have a hard time maintaining a constant temperature. I finally realized that it is more difficult to maintain a constant temperature inside an empty refrigerator than when it is filled. Once we precooled it and loaded it up with a couple of days worth of beverages and food for our trip, the temperature in the refrigerator stayed at a nearly constant 42 degrees with a range of about 41-44 degrees. This is slightly higher than the 38 degrees recommended by some sources but right at the recommendation from the US Food and Drug Administration which set the maximum refrigerator temperature at 41 degrees. (The 41 degrees is the max. for the products in the refrigerator and not the air temperature though.)

The unit is very quiet and we didn't hear it at night at all. (When shore power or solar power isn't available, the ACU monitors the supply battery voltage and adjusts the cooling cycle to minimize battery draw during those times.) Granted, we were camping close to the longest day of the year (and thus had a longer solar power cycle than other times of the year) but the house battery dropped to only about 12.6v by bedtime and was at about 12.5v or 12.4v in the middle of the night. By the time we got up in the morning, the solar was already recharging the house battery and it was back to around 12.6v. That was great to see since the old refrigerator was dropping the house battery to 12.2v at night!

With our original Norcold unit, we had to be vigilant about monitoring the refrigerator temperature and adjusting the thermostat during the day and at night to keep things cold enough but not too cold. This is not an issue with the Isotherm (in fact, the ACU automatically takes care of the thermostat issue although you can override the ACU and set a higher or lower temperature if desired). In addition, we always had a problem of freezing things like lettuce with the old Norcold. The Isotherm has a vegetable drawer in the bottom of the refrigerator which is perfect for that purpose. The built-in space in the door for milk and OJ containers and Coke cans is also very nice and makes the milk and OJ very easy to get in and out. In summary, we are very pleased with this unit and I think that it will certainly help conserve the house battery.

BTW, I also posted a very long message back in April about various electrical problems and concerns I was having regarding our house battery. Most of these got resolved via feedback on some wrong assumptions on my part. I never did find the short or other problem which seemed to be causing the solar to cycle on and off all day long but it has stopped doing that. (Unless the original refrigerator was causing the problem since I noticed that the problem stopped after I had the Isotherm installed....nah.) The Isotherm refrigerator seems to have really helped reduce the draw on the house battery too that I was concerned about. Since the house battery seemed to drop so fast, John Kalmbach suggested that I might need to equalize the house battery. The "battery condition" indicator on the inverter panel seemed to confirm that recommendation...that panel has three LED battery symbols and, although I don't consider those indications all that accurate, they did show that the house battery was in "poor" condition. I hadn't hooked up to shore power since adding solar a few years ago but did after installing the new refrigerator. I kept the shore power on for a couple of days while taking refrigerator temperature readings. Once I disconnected the shore power, I happened to notice that the inverter panel was now showing that the house battery was in "good" condition (the highest of the three levels). So, it seems that, at least for the time being, I've solved the house battery problem too.

Life is good....
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Old 06-22-2009, 11:29 AM   #9
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Re: Retrofitting a Isotherm refrigerator

My refrig is like yours and works the same way and I love it.

Angel
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Old 06-22-2009, 02:22 PM   #10
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Re: Retrofitting a Isotherm refrigerator

Whatever you do don't post any photos of the inside. It's hard enough to live with the Norcold just reading your posts.
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