Hi Chris, some comments inserted below.
SJ-Chris wrote:
Snip...
JBarca wrote:
Since I already have a fan up on the roof vent and a thermal disk switch to turn it on and off, I may switch the roof vent fan to the Fridge Defend. You just parallel the inside defrost fans with the roof vent fans. The ARP fan relay is rated at 20 amps, plenty for the milli amp fans I use, and the ARP defrost fans.
I'm not sure why you would want to tie your roof vent fan to your inside defrost fans. They aren't related in function. The Fridge Defend has a feature to control fan(s) that are placed behind the refrigerator to provide extra cooling to the coils behind the fridge and it seems like you'd want to use these controls for your vent fan.
(Side note: I'm also planning a DIY modification for putting fans behind the refrigerator controlled by a separate thermostat.)
I "was" use to be like you, "thinking" the inside fridge compartment fans were totally separate from the outside fans. I have been using a battery operated Camco inside fridge compartment fan for a long time thinking it was a good thing to do, help keep the air inside all stirred up. Right?
well... I never really thought about the whole situation with an absorption fridge. My brain was still thinking like a compressor driven fridge. Freon compressor systems pump cold air into the fridge compartment. Mixing that air up make senses plus the whole fridge is made to circulate air better inside then a RV style fridge that is packed to the gills most of the time.
The absorption fridge removes heat, and what is left is cold. Right?
Then there are those laws of physics that I keep forgetting some times... hot air rises! Now think of this inside the absorption fridge, the coil fins at the top of the inside fridge compartment are removing heat. The top of the fridge compartment area is where the thermistor sensor is located that cycles the cooling unit. We really only want the hot air up at the coils, we do not need cold air up there when the cooling unit is operating, we only want the inside hot air up at the inside fins/colis.
The air in the bottom of the fridge is colder since the hotter air is rising or already up top. This happens naturally for free. When I put my Camco battery operated fan in the fridge that runs constantly, in time it mixes up all the cold air and the hot air in the fridge. It is disturbing the natural, hot air rises natural process. And the thermistor is then negatively affected by the cold air being circulated around. Yes, in "time" and if no one opens the door, the whole fridge in time comes to equilibrium until the door opens again and new warmer food is put in. But how many times did the boiler have to run to accomplish this?
Once I thought through what is happening inside the fridge, the "ah ha!" moment came to me. You really do not want to stir up all the air inside the fridge, all the time. Just like the outside fans up in the roof vent, you only need the outside fans to run when the boiler is heating. This was simple to see on the outside fans as I wanted to save battery power for boondocking and have longer fan life not running when they did not have to. There is no real value running the outside fans when the boiler is off. The same thing applies to the inside fans if you are only using them to help stop frost/ice from building up on the fins inside the fridge compartment. Thus, inside fans and outside fans should run off the same signal if you decide to add inside defrost fans.
Here is the shorter version at ARP,
https://www.arprv.com/rv-fix-fridge-circulation-fan.phpDoes that help explain a change in thinking?
SJ-Chris wrote:
JBarca wrote:
Another reason for the Fridge Defend not yet mentioned is cold weather. I know you may not camp in cold down to freezing, and below, but in our area, freezing temps are here and we do winter camp.
If you want to get close to 32F outside or go below, the fridge as it stands in the stock configuration will slow down and may stop working. The heating may not stop, but the fluid can slow down flowing from what I have read. It seems Dometic does offer a lower vent hood that has some blocked off vents to lower the amount of cold air entering.
This Dometic lower vent is made for cold weather, just they do not list much else or fit the older Dometic vent frames. Norcold sells a cold weather kit to heat up a certain return tube on the cooling coil. Here is one of them. https://www.amazon.com/Norcold-634913-Cold-Weather-Kit/dp/B00T36VI30
I have not been able to find Dometic offering that heat strip. By using the heat strip on the Norcold and helping to reduce the cold air intake, it is reported you can go down to 0F. Some folks use an incandescent light bulb in the outside compartment.
The ARP system will help to shut off the boiler heat if the coolant stops flowing due to the cold weather for any reason.
Doug may be able to add some more to this and if he knows if Dometic offers a cold weather kit or do you just use the Norcold one? Most all of the older campers I restore have RM2652 fridges that I service.
Thanks
John
I will admit, I had not thought about ultra cold weather usage. I have been camping down to ~30*F and didn't have any issues with the refrigerator/freezer temps. I don't have immediate plans to camp down to 0*F. I'm guessing that the boiler getting hot to the touch does a fair job heating the cavity/space behind the refrigerator. But I can see how if it were 0*F outside and that cool air is being pulled in then maybe it could affect the cooling unit functionality. If I was going to camp in such temps I think I would consider putting something along the back side of the rear vent to limit the amount of air that could enter. That seems like it would allow the heat of the boiler to keep the air behind the refrigerator warm enough for proper operation. Not sure if that is true or not, but I'd start there.
I am big on safety. I do think it is important for safety and also to help protect your cooling unit from overheating damage to have some sort of high temp thermostat (either DIY or Fridge Defend) on your boiler to keep it below 220*C (428*F).
-Chris
Think about this thought, while you did camp down to approx 30F and your fridge appeared inside to be working OK, you really never know if it went into and out of, periods of the boiler is too hot or not. Some small damage may have happened and one would never know. Being below freezing temps, even at 28F etc, and the wind blowing against the side of the fridge vents, changes the amount of excess heat off the boiler. This may well have been going on with my fridge also.
Here in Ohio, we camp all year round. Granted not a lot of winter below freezing at night camping, but spring through fall is very common. Cold snaps overnight in the spring and late fall below freezing exist regularly. How many times did the boiler cycle over night? Who knows, but now we realize what can happen when boiler temps go out range and damage starts to creep in.
You have a good thread here bringing all this up.
John
PS, You have 3 campers, I have 5 of them... Don't we all need a few spares? :B We have our main camper we use all the time shown in my sig, and 4 older, very wet project campers. One of the project campers is fully restored, one is partly restored and the other two are in many pieces drying out waiting to get restored. I also seem to have many friends needing water damage repair, some small damage, others are full restores. I have just completed my 16th water damaged camper repair. I'm either nuts or like doing this extremely time consuming restoring process. Winter is coming and I'm hoping I can get back onto one of my project campers.
