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> Ammonia Fridge 101

SidecarFlip
post May 5 2017, 08:24 PM
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Group: Members
Posts: 472
Joined: 15-October 16
Member No.: 9,221
Favorite Truck Camper(s): Forest River Palomino SS
Type and Brand of Truck(s) Owned: 1997 Ford F350 4x4 LB SRW CC 7.3 diesel
Type of Tiedowns used: HappyJac standard
Truck and Camper Setup: 1997 Ford F350 4 door 4x4 Crew Cab 7.3 Diesel, Lance 915 loaded, 2015 Palomino SS1500 Loaded



Lets call this a tutorial on how to get your 2 way or 3 way fridge working (and maintaining interior temperature like a compressor (residential) fridge without buying one (expensive)....

The inherent issue with an ammonia fridge is, without proper air circulation in the rear cavity, the unit has a difficult time transferring the refrigerated compartment heat to the ammonia solution that circulates by thermosiphon and gravity in the coils and cools the interior.

In most TC's today, ammonia fridges are compromised, by install space and the ability to draw in adequate amounts of cool air to cool the external condenser (at the top of the fridge in the outside cavity, especially pop up TC's like I own.

The solution is, to add external fans to the cavity but location is critical. The location of the fan or fans has to be directly in front of the upper condenser, blowing out. That causes a negative pressure below the condenser and pulls cool ambient air in the bottom intake (access panel and exhausts it out the top, constantly exposing the condenser to cooling air. The cooler the upper condenser runs, the better heat absorbtion the interior evaporator (inside the fridge works.

As a test, I opened up my upper vent (which came with one small DC fan, removed that and replaced it with 2 Fluid Dynamic Bearing 120mm computer muffin fans, the fans mounted as close to the evaporator as I coud get them. I wired the fans to the existing Dometic snap disc thermostat (80 on - 60 off) that was attached to the outer cooling fin on the evaporator but you can purchase a snap disc thermostat at Grainger or Dell City Electronics for a couple bucks if you have no present fans.

I wired them to the hot accessory terminal on the Dometic control board.

I also added additional insulation to the cavity between the fridge body and the cabinet, about 1/2 rool actually. I also added a a sheet metal baffle on the top and backside of the upper evaporator to direct the airflow into the fans and reduce turbulence.

The result is: From ambient to 34 degrees interior temp., it takes about2 hours to cool down and it maintains 34 degrees +- 3 gegrees, no matter what temp it is outside or if the sun is shining on the refrigerator side of the camper.

Hard side campers can also benefit from cooling fans, but placement of the fans needs to be in the upper chimney portion, below the roof cap.

I've been ruinning my unit for a week straight now and using a digital recording thermostat to monitor the interior termps. +-3 degrees from set point at all times.

Prior to modifying the fridge, the only way I could maintain even 40 interior temp was to have the control set on maximum cold. Now, I'm running on setting 2 with three to go and the fridge is auto cycling, that is, shutting down and restarting as needed.

The only drawback is current consumption. The fans together pull 1.2 amps running and the fridge pulls about 2/10 amp. While that might become an issue off grid over many days on battery power, it's a lot less than a compressor fridge which normally pulls around 6 amps.

What really impresses me is the ability to hold pre set temperature with little fluctuation and the ability for the fridge to shut down and restart on it's own. Last year, the fridge ran continuously and never cycled and the interior temps swung wildly.

No more. Easy modification too. Cost, about 30 bucks and a couple hours of your time.
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Torsten
post May 8 2017, 03:37 PM
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From: Germany
Member No.: 9,245
Favorite Truck Camper(s): Lance Model 780
Type and Brand of Truck(s) Owned: 1985 Ford F250 Diesel
Type of Tiedowns used: Happijac
Truck and Camper Setup: 1985 Ford F250 Diesel with Lance Model 780



Hi Flip,

did you have Pictures? looks like a realy great idea!

Best regards

Torsten
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SidecarFlip
post May 9 2017, 09:59 PM
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Group: Members
Posts: 472
Joined: 15-October 16
Member No.: 9,221
Favorite Truck Camper(s): Forest River Palomino SS
Type and Brand of Truck(s) Owned: 1997 Ford F350 4x4 LB SRW CC 7.3 diesel
Type of Tiedowns used: HappyJac standard
Truck and Camper Setup: 1997 Ford F350 4 door 4x4 Crew Cab 7.3 Diesel, Lance 915 loaded, 2015 Palomino SS1500 Loaded



No. I probably should have taken pictures, didn't think about it until after I buttoned up the outer upper vent with Butyl tale and reattached it.

Pretty straightforward. Inn a vertical (roof vent fridgr) you just add a cooling fanr in the upper stack, just below the roof cap, blowing op. That will greatly increase the already natural draft the heat coming off the condenser makes.

Camco, also sells a solar powered roof vent with a built in fan but I prefer a 12 volt wired unit. better CFM draw. Side mount units like I have make no natural draft and require 12 volt muffin fan(s) to induce the draft.

If my unit pooped out, I'd not hesitate to replace it with a Danfoss Compressor Fridge but you have to allow for amp draw which is around 6 amps at 100% duty cycle. A propane fridge pulls about 2/10ths of an amp fans off and 1.8 amps with 2 120mm high velocity muffin fans running.
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