absorption refrigerator out of level, boiler temp control

[SJ-Chris]

Safety is important!


Consider a scenario where someone parks for the night (or for several days) on a steep driveway or side of the road on a hill and they are very unlevel. Assume they have their absorption refrigerator on. Without some form of temperature protection (ie. Fridge Defend, or DIY thermostat solution) this seems like it could be a dangerous situation (fridge damage and/or fire). I sometimes let others use my RVs. I tell them the refrigerator needs to be level, but most non-RVers don't really understand the importance, or they don't care because the RV isn't theirs.


I have seen from multiple posts and websites, that under "normal" operation of a "level" absorption refrigerator the boiler temperature will be ~180-190*C with either propane or plugged in.


I understand that when your refrigerator is out of level by too much (more than 3% refrigerator side-to-side or 6% refrigerator front-to-back) then the gravity functionality of some of the internal liquids in your cooling unit can stop flowing where they are supposed to flow. This can cause (blockage?) the boiler temperature to increase. Once it gets "too hot" (...I've seen on Fridge Defend's video that value is around 225*C) boiling can happen and damage can occur.


Q1: Is it accurate to say that as long as the boiler temperature is kept under some value (220*C? 210*C? 205*C?) your cooling unit will not get damaged/corroded and it will unlikely cause a refrigerator fire?


Q2: If your refrigerator is out of level (more than 3% / 6%) and continues to run, but a thermostat (or Fridge Defend) keeps the boiler from going over say 210*C, what will happen? Imagine a thermostat that cuts off refrigerator power at 210*C but then turns the refrigerator back on at 170*C and the boiler temp floats back and forth between 170*C and 210*C but the refrigerator is well out of level. What will happen? Does cooling stop because the liquids cannot flow where they need to flow? Does pressure in the system keep the fluids flowing even if off level? Does the internal temperatures of the interior of the freezer/refrigerator climb to ambient outside temperatures?


Q3: Does anyone have any examples of when their boiler got up to 300*C, 400*C, etc. Can it get that hot under some strange scenarios?


What I'm planning on doing is a DIY modification where a high temp thermostat will turn off the refrigerator once the boiler temp hits some value (ie. 210*C) and then turn it back on once it drops back down to 170*C. This will act as a high temperature protector on the boiler. Under normal operation, the boiler temp will likely not get over 190*C so things will work as they should. In the event that the refrigerator gets unlevel (or some other problem) and the temps start climbing, the thermostat will shut it off before it gets dangerous. Does anyone see anything wrong with simply cutting off refrigerator power if it hits 210*C and then restoring power once it has cooled back down to 170*C? Seems reasonable to me. Just want to check to see if I'm missing anything.


For safety reasons, I think most people with an absorption refrigerator should have something to cut off an overheating boiler situation (either a Fridge Defend or DIY thermostat) to reduce the risk of damaging their cooling unit and/or starting a fire (worst case scenario). Maybe the risk is small(?), but my DIY fix will likely only cost me $25 and an hour of time.


Thoughts?
Chris

[SJ-Chris]

SJ-Chris wrote:
I have received and bench tested the thermostat I purchased for this mod so that I know how it works. Haven't played with the bonus app yet, but that should be fun.

https://www.amazon.com/Temperature-Controller-99%C2%B0C-999%C2%B0C-One-Channel-Thermocouple/dp/B09TT7VWCK

Pretty straightforward once I figured things out. This thermostat operates a relay. I will ultimately run the 12v power going to the refrigerator control board from the "on/off" button control inside the RV through the relay. This should cover either AC or propane operation (they both require the 12v supply to the refrigerator control board). That same 12v line will supply power to this thermostat device, so it will only be on when the refrigerator is on (no power draw while in storage).

I can set a high "turn off" temperature and will likely have that at 200*C (392*F) (assuming that "normal/level" steady boiler temperature is ~180*C (356*F)...I will test this once it is installed). My understanding is the primary goal of this, or similar, device is to simply keep the internal water in the cooling unit from boiling (220-225*C...428*F-437*F...and higher). (side note: If you are wondering WHY the water boiling point is so high inside the cooling unit it is because the system is under a lot of pressure during operation.) If the boiler hits 200*C (perhaps by being out of level), the 12v power to the refrigerator will be killed (which will be sort of equivalent to turning the refrigerator off at the main "on/off" button) until the temperature drops down to some set point and then it will turn back on automatically (nice...this is what we want). I'm not sure what temp I should set this drop down temperature to. Any thoughts?

If it turns off at 200*C, do I want it turning back on once it drops down to 180*C? 150*C? 70*C? Unless someone explains otherwise, I think I'll have it turn back on once the boiler cools down to 170*C (338*F). That would be a 30*C cooling off period (from 200*C) which I'm guessing would take 10-20 minutes (??? I'll try to do a test to find out once I install it). Then the refrigerator would turn on again and try again. If the conditions were still present that was causing it to start overheating in the first place (ie. being too far out of level), then the boiler temperature would slowly rise up to 200*C and then bounce back and forth between 200*C and 170*C. Any harm in this??

Or would it be better to have the boiler temperature bounce between 200*C and 180*C such that refrigerator interior cooling can hopefully still be taking place and the interior of the refrigerator can get to its desired temps and then the regular refrigerator controls would shut down the refrigerator until it needs to cycle on again naturally?

I'm guessing it probably doesn't matter too much if the "turn back on" temperature is 180*C, 170*C, 150*C, etc. The main purpose/function is to simply limit the overheating such that it never gets above 220*C (428*F). I'm still pretty stunned to know that Norcold and Dometic find it okay to let the boiler temp get all the way up to 750-800*F before their kill fuse blows (at which time, correct me if I am wrong, the fuse will need to be physically replaced before your refrigerator will work again). With my ~$25 mod it will cut the power if it gets just 36*F above normal operating temps and then turn itself back on once the boiler temp gets back down to normal.

Above, otrfun posted their refrigerator boiler temp data from a 2 year period where they made no efforts to keep their fridge level during operation. It rose above their normal boiler temp range a max of 7-12*C (21*F max) so it seems like in general these boilers hold a pretty constant max temperature. (Thanks for the data otrfun!)

I have some family in town for Christmas so the install will likely have to wait until early January.

-Chris

[SJ-Chris]

I have received and bench tested the thermostat I purchased for this mod so that I know how it works. Haven't played with the bonus app yet, but that should be fun.

https://www.amazon.com/Temperature-Controller-99%C2%B0C-999%C2%B0C-One-Channel-Thermocouple/dp/B09TT7VWCK

Pretty straightforward once I figured things out. This thermostat operates a relay. I will ultimately run the 12v power going to the refrigerator control board from the "on/off" button control inside the RV through the relay. This should cover either AC or propane operation (they both require the 12v supply to the refrigerator control board). That same 12v line will supply power to this thermostat device, so it will only be on when the refrigerator is on (no power draw while in storage).

I can set a high "turn off" temperature and will likely have that at 200*C (392*F) (assuming that "normal/level" steady boiler temperature is ~180*C (356*F)...I will test this once it is installed). My understanding is the primary goal of this, or similar, device is to simply keep the internal water in the cooling unit from boiling (220-225*C...428*F-437*F...and higher). (side note: If you are wondering WHY the water boiling point is so high inside the cooling unit it is because the system is under a lot of pressure during operation.) If the boiler hits 200*C (perhaps by being out of level), the 12v power to the refrigerator will be killed (which will be sort of equivalent to turning the refrigerator off at the main "on/off" button) until the temperature drops down to some set point and then it will turn back on automatically (nice...this is what we want). I'm not sure what temp I should set this drop down temperature to. Any thoughts?

If it turns off at 200*C, do I want it turning back on once it drops down to 180*C? 150*C? 70*C? Unless someone explains otherwise, I think I'll have it turn back on once the boiler cools down to 170*C (338*F). That would be a 30*C cooling off period (from 200*C) which I'm guessing would take 10-20 minutes (??? I'll try to do a test to find out once I install it). Then the refrigerator would turn on again and try again. If the conditions were still present that was causing it to start overheating in the first place (ie. being too far out of level), then the boiler temperature would slowly rise up to 200*C and then bounce back and forth between 200*C and 170*C. Any harm in this??

Or would it be better to have the boiler temperature bounce between 200*C and 180*C such that refrigerator interior cooling can hopefully still be taking place and the interior of the refrigerator can get to its desired temps and then the regular refrigerator controls would shut down the refrigerator until it needs to cycle on again naturally?

I'm guessing it probably doesn't matter too much if the "turn back on" temperature is 180*C, 170*C, 150*C, etc. The main purpose/function is to simply limit the overheating such that it never gets above 220*C (428*F). I'm still pretty stunned to know that Norcold and Dometic find it okay to let the boiler temp get all the way up to 750-800*F before their kill fuse blows (at which time, correct me if I am wrong, the fuse will need to be physically replaced before your refrigerator will work again). With my ~$25 mod it will cut the power if it gets just 36*F above normal operating temps and then turn itself back on once the boiler temp gets back down to normal.

I have some family in town for Christmas so the install will likely have to wait until early January.

-Chris

[Vintage465]

SJ-Chris wrote:

Vintage465 wrote:
I guess today I'm going to "be that guy"........I grew in a family that owned an RV sales and repair shop.....in the days that if you ran your fridge out of level(propane or electric)it would lockup in 20 minutes. The law was "not level, don't light". The repair was to remove the fridge turn it on it's head for 24 hours, reinstall and fire it up...level of course. 99% of the time it fixed it. So my question is, why hypothetically set your self up to do damage to your fridge when it just needs to be level. Yes I get it that driveways and streets aren't level, but.........I'll stick by "not level, don't light".

Your suggestion is fair enough...

I'm curious...Do refrigerators still "lock up" due to running out of level? Or is that a thing of the past?

I've heard about the "turn your fridge upside down" trick to "reset" the fluids (I guess?). Better than buying a new refrigerator if it fixes the problem, but somewhat painful to have to remove the refrigerator to stand it upside-down.

To answer your question...I personally try to remember not to have the refrigerator on if I'm parked significantly off-level (more than 3 degrees side to side or 6 degrees front to back). But I could always forget. More importantly, I let others use my RVs. When I do, I give them a tour inside and out showing them how everything works. It's a lot of info to communicate how every feature/etc on an RV works. It is likely that when I tell them "don't run the refrigerator if you are out of level" it goes in one ear and out the other.

So ultimately, if I want to guarantee the refrigerator doesn't run and overheat (and cause damage) when it is out of level, I can DIY a $25 fix with a high temp thermostat to shut it off. In a sense, it just automates/forces the shut off process if out of level to a point of causing damage so that I or others never need to "remember" not to run it off-level.

At the end of the day, adding a Fridge Defend or $25 DIY thermostat IS a risk reduction activity. It WILL eliminate the overheating of the boiler which WILL reduce potential damage over time and reduce the chances of a fire. Everyone gets to make their own decision on whether that risk is tiny, small, medium, high, or extreme. In my mind, if this overheating issue was ONLY about potential damage to the cooling unit over time that could cause premature death of the cooling unit and nothing else, it probably wouldn't bother me as much. But it makes me uncomfortable that something could overheat up to as much as 750*F-800*F and ultimately cause a fire in the RV (worst case scenario). If I can eliminate that risk for $25, to me it is worth it.

Happy Camping!
Chris

Actually, I haven't study'd or researched if they can lock up now a days. I think they they have some kind of vapor or boiling bypass now days. I've also heard running them off level is dangerous to the refer's health. I just make sure I don't do it.

[SJ-Chris]

dougrainer wrote:
Once you have ANY blockage small or large or complete, Burping the refer(removing and standing on its side or top for 24 hours and then reinstalling,DOES NOT FIX THE CONDITION. It will allow some cooling a little better than before burping, but the problem is still there and after a few days/weeks the original blockage problem will diminish cooling. As I stated, the blockage is as hard as a weld and the cooling unit tube at the top must be cut off and a new upper tube welded in place and then recharge. Doug

Makes sense and I believe you.

Seems important to do what we can to avoid the incremental blockage as much as possible to help extend the life of the cooling unit.

I had one cooling unit fail about 2 years ago. I replaced the cooling unit myself with an Amish built one and it has been functioning great ever since (...much colder than my other refrigerators). I do not know the root cause of the failure in that cooling unit. There was no leaking ammonium that I could see or smell. The boiler worked and heated fine, but it just stopped cooling. Blockage perhaps?

-Chris

[SJ-Chris]

JBarca wrote:
Hi Chris, some comments inserted below.

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.php

Does that help explain a change in thinking?

You have given some great info about internal air flow/fans/etc INSIDE the fridge...thanks. I hadn't given it much thought. It sounds like from what you have mentioned that the inside the fridge fan should be ON only when the BOILER is on (irrespective of when the roof vent fan is on). If you have a fan INSIDE the refrigerator.

To date, I have not been thinking about putting a fan INSIDE the refrigerator. My internal temps seem fine. I have never done a test to see the temp difference between the bottom shelf vs the top shelf (empty, and/or stuffed with items). Would be interesting to see if there is a temp difference. Anyone know??

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.

I haven't thought about cold weather (below 30*F) camping. I know now, based on learning more about how these refrigerators work, that it would be a good idea to place a heat source in the space behind the refrigerator (ie. 100w light bulb, etc). Sounds like that will help.

You have a good thread here bringing all this up.

John

Thanks! I'm enjoying learning from everyone's knowledge/experience.

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.

Sounds like you enjoy restoring them....good stuff!

I have 3 because I use them for a unique business idea (...one that is much better than simply renting them out 🙂 ). But I also enjoy doing modifications on them for safety, or comfort, or just for fun. I think I'm addicted!

-Chris

[dougrainer]

Once you have ANY blockage small or large or complete, Burping the refer(removing and standing on its side or top for 24 hours and then reinstalling,DOES NOT FIX THE CONDITION. It will allow some cooling a little better than before burping, but the problem is still there and after a few days/weeks the original blockage problem will diminish cooling. As I stated, the blockage is as hard as a weld and the cooling unit tube at the top must be cut off and a new upper tube welded in place and then recharge. Doug

[JBarca]

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.php

Does 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.

[SJ-Chris]

Vintage465 wrote:
I guess today I'm going to "be that guy"........I grew in a family that owned an RV sales and repair shop.....in the days that if you ran your fridge out of level(propane or electric)it would lockup in 20 minutes. The law was "not level, don't light". The repair was to remove the fridge turn it on it's head for 24 hours, reinstall and fire it up...level of course. 99% of the time it fixed it. So my question is, why hypothetically set your self up to do damage to your fridge when it just needs to be level. Yes I get it that driveways and streets aren't level, but.........I'll stick by "not level, don't light".

Your suggestion is fair enough...

I'm curious...Do refrigerators still "lock up" due to running out of level? Or is that a thing of the past?

I've heard about the "turn your fridge upside down" trick to "reset" the fluids (I guess?). Better than buying a new refrigerator if it fixes the problem, but somewhat painful to have to remove the refrigerator to stand it upside-down.

To answer your question...I personally try to remember not to have the refrigerator on if I'm parked significantly off-level (more than 3 degrees side to side or 6 degrees front to back). But I could always forget. More importantly, I let others use my RVs. When I do, I give them a tour inside and out showing them how everything works. It's a lot of info to communicate how every feature/etc on an RV works. It is likely that when I tell them "don't run the refrigerator if you are out of level" it goes in one ear and out the other.

So ultimately, if I want to guarantee the refrigerator doesn't run and overheat (and cause damage) when it is out of level, I can DIY a $25 fix with a high temp thermostat to shut it off. In a sense, it just automates/forces the shut off process if out of level to a point of causing damage so that I or others never need to "remember" not to run it off-level.

At the end of the day, adding a Fridge Defend or $25 DIY thermostat IS a risk reduction activity. It WILL eliminate the overheating of the boiler which WILL reduce potential damage over time and reduce the chances of a fire. Everyone gets to make their own decision on whether that risk is tiny, small, medium, high, or extreme. In my mind, if this overheating issue was ONLY about potential damage to the cooling unit over time that could cause premature death of the cooling unit and nothing else, it probably wouldn't bother me as much. But it makes me uncomfortable that something could overheat up to as much as 750*F-800*F and ultimately cause a fire in the RV (worst case scenario). If I can eliminate that risk for $25, to me it is worth it.

Happy Camping!
Chris

[Vintage465]

I guess today I'm going to "be that guy"........I grew in a family that owned an RV sales and repair shop.....in the days that if you ran your fridge out of level(propane or electric)it would lockup in 20 minutes. The law was "not level, don't light". The repair was to remove the fridge turn it on it's head for 24 hours, reinstall and fire it up...level of course. 99% of the time it fixed it. So my question is, why hypothetically set your self up to do damage to your fridge when it just needs to be level. Yes I get it that driveways and streets aren't level, but.........I'll stick by "not level, don't light".

[SJ-Chris]

otrfun wrote:

SJ-Chris wrote:
. . . I'm a DIYer and I enjoy tinkering with modifications . . . I believe a simple high temp thermostat can easily accomplish this task, and they only cost $20. If I only had 1 RV I would probably still just buy a Fridge Defend. But I've got 3 RVs. So if I can implement this DIY fix it will save me 3x the money.

Have you found a suitable 200c sensor and control board combination that operates on 12vdc? IMO realworld temperature accuracy and overall, proven reliability may potentially be the biggest hurdle.

Who wouldn't love a reliable, low-cost alternative to the $200+ FD?! 🙂

I bought this high temp thermostat to try out.

https://www.amazon.com/gp/product/B09TT7VWCK

Cost was $20. One thing that looked interesting is that it has an app so you can track things on your phone, export the data, etc. I'm not sure, but I don't think Fridge Defend does that. If the app works, that will just be a bonus (...I couldn't find it in the app store and I was paranoid about scanning their QR code).

I bought a tiny clear plastic box for it to go in. The screw in probe housing was easy to slide down the wire so that there is just a cylinder probe end. I will attach it to the boiler tube with a hose clamp like this:
https://www.homedepot.com/p/Everbilt-1-2-1-1-4-in-Stainless-Steel-Hose-Clamp-6712595/202309385

I hope to get to this project in the next couple of weeks. I'll keep you posted.

-Chris

[otrfun]

SJ-Chris wrote:
. . . I'm a DIYer and I enjoy tinkering with modifications . . . I believe a simple high temp thermostat can easily accomplish this task, and they only cost $20. If I only had 1 RV I would probably still just buy a Fridge Defend. But I've got 3 RVs. So if I can implement this DIY fix it will save me 3x the money.

Have you found a suitable 200c sensor and control board combination that operates on 12vdc? IMO realworld temperature accuracy and overall, proven reliability may potentially be the biggest hurdle.

Who wouldn't love a reliable, low-cost alternative to the $200+ FD?! 🙂

[dougrainer]

The best way in sub 20 (F) weather is just a 120 volt 40 watt incandescent light bulb installed in the area behind the refer. In sub 20 degree weather the Refer will not cool at all. The sub cold weather kits I have never seen or ever needed. Texas is not an area that would require them. Doug

[SJ-Chris]

Hi John. Good post.

JBarca wrote:
Chris, I have been following your post.

I did review the ARP system a while back, just never made it to installing any, yet. I called and talked with them today. They are very down to earth, and they are a, know what they are doing company.

I have visited the ARP site and seen many many posts from the makers of Fridge Defend on some online forums. It seems like they have a good product AND they seem to be genuinely passionate about safety. Very knowledgeable. Seem like nice people. Seems like they want to help people.

JBarca wrote:

I am going with the Fridge Defend V5.11 with the fan control. I want to add the defrost fans inside the fridge and to cycle them you need the fan control version. The V5.11 has an alarm, so you know when you have a problem and you and tweak the settings as needed. Since most all the fridges I work on are older, there may be some level of coolant damage from prior owners, so the fridge may have limited life, but having the fire safety part is a big plus.

If you are looking for an integrated system that controls the boiler temp, the fan(s) behind the refrigerator, and fans inside the refrigerator, then the Fridge Defend is definitely for you.

I'm not anti-Fridge Defend...I think they have a great product. But I'm a DIYer and I enjoy tinkering with modifications. I personally believe that from a safety standpoint, the most important thing on these absorption refrigerators is to keep the boiler under 220*C. I believe a simple high temp thermostat can easily accomplish this task, and they only cost $20. If I only had 1 RV I would probably still just buy a Fridge Defend. But I've got 3 RVs. So if I can implement this DIY fix it will save me 3x the money.

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.)

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

[JBarca]

Chris, I have been following your post.

I did review the ARP system a while back, just never made it to installing any, yet. I called and talked with them today. They are very down to earth, and they are a, know what they are doing company.

I am going with the Fridge Defend V5.11 with the fan control. I want to add the defrost fans inside the fridge and to cycle them you need the fan control version. The V5.11 has an alarm, so you know when you have a problem and you and tweak the settings as needed. Since most all the fridges I work on are older, there may be some level of coolant damage from prior owners, so the fridge may have limited life, but having the fire safety part is a big plus.

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.

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