Jump to content

Fridge - gas lighting issue


Recommended Posts

Hi

I have a fridge that can be powered by gas and electric. I have used the electric to power it and it works fine. I can't get the gas lit. I have followed the instructions and see the little spark going off in the tiny window and then it fades and goes out.

 

Any advice gratefully received.

 

Thanks!

Link to comment
Share on other sites

1 hour ago, BBC3 said:

I can't get the gas lit.

One thing to check is to make sure the line is fully purged.  Light the stove and make sure a burner stays fully lit.  Then turn that off and go back to trying the fridge again.  I have to hold down the pilot button and then click the igniter and keep holding the pilot button/valve open while looking through the tiny window to make sure the flame is on.  After like 30 to 45 seconds i can let go of the pilot push button/valve and then the pilot will stay lit.  If it let it go too soon it won't stay lit.  Sometimes I have to light it several times to get it to stay lit, all the while holding the pilot valve button in. Usually in these things the flame has to heat up a thermocouple that makes the pilot valve stay open, plus further purging might be needed in this initial lighting process.  

If this doesn't work then you might need to get into the guts of the burner and make sure it's all clean and the themocouple is in the pilot flame.   You are getting something to light (it just goes out) so it sounds like the igniter is working and there is some gas there.  These are good signs.

Link to comment
Share on other sites

2 minutes ago, AtlantaCamper said:

One thing to check is to make sure the line is fully purged.  Light the stove and make sure a burner stays fully lit.  Then turn that off and go back to trying the fridge again.  I have to hold down the pilot button and then click the igniter and keep holding the pilot button/valve open while looking through the tiny window to make sure the flame is on.  After like 30 to 45 seconds i can let go of the pilot push button/valve and then the pilot will stay lit.  If it let it go too soon it won't stay lit.  Sometimes I have to light it several times to get it to stay lit, all the while holding the pilot valve button in. Usually in these things the flame has to heat up a thermocouple that makes the pilot valve stay open, plus further purging might be needed in this initial lighting process.  

If this doesn't work then you might need to get into the guts of the burner and make sure it's all clean and the themocouple is in the pilot flame.   You are getting something to light (it just goes out) so it sounds like the igniter is working and there is some gas there.  These are good signs.

Thanks. I'll give it a try now.

Link to comment
Share on other sites

13 minutes ago, AtlantaCamper said:

One thing to check is to make sure the line is fully purged.  Light the stove and make sure a burner stays fully lit.  Then turn that off and go back to trying the fridge again.  I have to hold down the pilot button and then click the igniter and keep holding the pilot button/valve open while looking through the tiny window to make sure the flame is on.  After like 30 to 45 seconds i can let go of the pilot push button/valve and then the pilot will stay lit.  If it let it go too soon it won't stay lit.  Sometimes I have to light it several times to get it to stay lit, all the while holding the pilot valve button in. Usually in these things the flame has to heat up a thermocouple that makes the pilot valve stay open, plus further purging might be needed in this initial lighting process.  

If this doesn't work then you might need to get into the guts of the burner and make sure it's all clean and the themocouple is in the pilot flame.   You are getting something to light (it just goes out) so it sounds like the igniter is working and there is some gas there.  These are good signs.

So, I just lit all the burners on the stove and they all work fine. I then did the fridge and it loooks like it is lit. But, the tiny glass viewing area is small...and the light coming from it is tiny, and I'm not 100% sure it is lit. So, I turned it off and the tiny light disappeared, leaving me thinking that it is lit. I understand it takes 4 - 8 hours to cool down a fridge like this, so I might just leave it and see what happens.......any other way to tell if it is lit?

Link to comment
Share on other sites

20 minutes ago, AtlantaCamper said:

One thing to check is to make sure the line is fully purged.  Light the stove and make sure a burner stays fully lit.  Then turn that off and go back to trying the fridge again.  I have to hold down the pilot button and then click the igniter and keep holding the pilot button/valve open while looking through the tiny window to make sure the flame is on.  After like 30 to 45 seconds i can let go of the pilot push button/valve and then the pilot will stay lit.  If it let it go too soon it won't stay lit.  Sometimes I have to light it several times to get it to stay lit, all the while holding the pilot valve button in. Usually in these things the flame has to heat up a thermocouple that makes the pilot valve stay open, plus further purging might be needed in this initial lighting process.  

If this doesn't work then you might need to get into the guts of the burner and make sure it's all clean and the themocouple is in the pilot flame.   You are getting something to light (it just goes out) so it sounds like the igniter is working and there is some gas there.  These are good signs.

Also, you have any idea how much gas I'd need to run just the fridge each day is i use my Honda 1000 generator?

Link to comment
Share on other sites

37 minutes ago, BBC3 said:

how much gas I'd need to run just the fridge each day

Are you asking about gas as in gasoline or gas as in propane?  It takes very little propane to run the fridge.  It takes uses a small flame to generate the heat it needs to work.  Using the Honda generator is very inefficient as it would take a lot of gasoline to generate the small amount of electricity needed to run the 115VAC heater.  You can get about 2 to 3 days (I'm told by a fiend) running the fridge on a battery if that's the only thing it's doing.  Also very inefficient.  Propane is the way to go on the fridge.

Sounds like you got it fired up!  Great!   It is really hard to see the flame in that stupid prisim indicator thingy.  I have to squint and block out all the light and I still wonder if I'm really seeing the flame or not. Just something one has to deal with. 

Yes, it takes a very long time to get cold.  You will know it's working if you open the back hatch and feel the hot burner area where it's boiling the ammonia and then you will feel the cold on the fins inside.  I start mine up the day before I leave. I leave it on propane while driving though others turn it to 12v.  I had issues with the flame blowing out while driving but proper adjusting of all of the baffles and it hasn't gone out since while driving.

These RV fridges work by boiling ammonia with a heater (propane, 12v or electric), then the ammonia gas absorbs heat when it goes through the system and eventually condenses back into liquid ammonia.  Then it boils again and round and round it goes.  To work efficiently you have to get rid of the heat from the fins on the very top of the back panel .  Make sure air flow isn't blocked in the rear.    

I have gone to a system myself where I use the fridge in parallel with a small Yeti-clone cooler.  I put drinks and ice (like ~5 to 6 pounds per day usage) in the cooler and other stuff in the fridge.  If you put warm stuff (like room temp beer) in the fridge it takes a LONG time to cool them down and robs the fridge of most of it's cooling power.  ONly cold things should go in the fridge and limit the time the door is open.  An ammonia fridge can get cold, but it' just can't move a large volume of heat.  If you work with these limitations you will enjoy it.

Link to comment
Share on other sites

Boring math... A typical small 4 CF RV fridge uses about 850 BTU per hour. There 91,000 btu's in a gallon of propane so a gallon of propane is worth about 120 hours in average temps.

A 100-degree temp will bring usage to 1400 btu or 3 days per gallon.

A honda1000 will run the same refer about 8 hr per gallon of gas +ware and tear on the engine.                                            

Link to comment
Share on other sites

2 minutes ago, WME said:

Boring math...

Very useful numbers, thanks WME!  3 days per gallon of propane at 100F is really quite good I think and this is pretty much worst case scenario.  

Link to comment
Share on other sites

1 hour ago, AtlantaCamper said:

Are you asking about gas as in gasoline or gas as in propane?  It takes very little propane to run the fridge.  It takes uses a small flame to generate the heat it needs to work.  Using the Honda generator is very inefficient as it would take a lot of gasoline to generate the small amount of electricity needed to run the 115VAC heater.  You can get about 2 to 3 days (I'm told by a fiend) running the fridge on a battery if that's the only thing it's doing.  Also very inefficient.  Propane is the way to go on the fridge.

Sounds like you got it fired up!  Great!   It is really hard to see the flame in that stupid prisim indicator thingy.  I have to squint and block out all the light and I still wonder if I'm really seeing the flame or not. Just something one has to deal with. 

Yes, it takes a very long time to get cold.  You will know it's working if you open the back hatch and feel the hot burner area where it's boiling the ammonia and then you will feel the cold on the fins inside.  I start mine up the day before I leave. I leave it on propane while driving though others turn it to 12v.  I had issues with the flame blowing out while driving but proper adjusting of all of the baffles and it hasn't gone out since while driving.

These RV fridges work by boiling ammonia with a heater (propane, 12v or electric), then the ammonia gas absorbs heat when it goes through the system and eventually condenses back into liquid ammonia.  Then it boils again and round and round it goes.  To work efficiently you have to get rid of the heat from the fins on the very top of the back panel .  Make sure air flow isn't blocked in the rear.    

I have gone to a system myself where I use the fridge in parallel with a small Yeti-clone cooler.  I put drinks and ice (like ~5 to 6 pounds per day usage) in the cooler and other stuff in the fridge.  If you put warm stuff (like room temp beer) in the fridge it takes a LONG time to cool them down and robs the fridge of most of it's cooling power.  ONly cold things should go in the fridge and limit the time the door is open.  An ammonia fridge can get cold, but it' just can't move a large volume of heat.  If you work with these limitations you will enjoy it.

Thanks so much for taking the time and sharing this info with me today. It is useful to me. I'm a beginner and so soaking all this up. Yeah, that tiny little light, I was straining my eyes and not sure what I was seeing in the end - Ha! But - after a bit of checking, on the items you suggested, I can tell - the fridge is working!! To be able to operate just on propane is great! I like the idea you speak of with the cooler and I'll probably end up doing that too. Thanks again for taking the time with me. Cheers! 

Link to comment
Share on other sites

Thanks for sharing this info - it is useful to me to get an idea. I appreciate you taking the time to post it. I'm learning plenty here and appreciate it!

Link to comment
Share on other sites

58 minutes ago, AtlantaCamper said:

Very useful numbers, thanks WME!  3 days per gallon of propane at 100F is really quite good I think and this is pretty much worst case scenario.  

Yeah, thanks - it's all good learning for me on this site, and i really appreciate you and others being willing to take your time to share knowledge with a beginner like me!

 

Cheers!

Link to comment
Share on other sites

1 hour ago, WME said:

Boring math... A typical small 4 CF RV fridge uses about 850 BTU per hour. There 91,000 btu's in a gallon of propane so a gallon of propane is worth about 120 hours in average temps.

A 100-degree temp will bring usage to 1400 btu or 3 days per gallon.

A honda1000 will run the same refer about 8 hr per gallon of gas +ware and tear on the engine.                                            

Thank you. This is good info. I appreciate you taking the time to share with me. Many thanks!

Link to comment
Share on other sites

I kinda forgot to turn mine off once and 2 months later when I got ready to go camping it was all ready nice and cool!

 

Link to comment
Share on other sites

18 minutes ago, Maineah said:

I kinda forgot to turn mine off once and 2 months later when I got ready to go camping it was all ready nice and cool!

 

Ha! Big tank of propane!!

 

Link to comment
Share on other sites

Shade helps a lot it was in the barn and it actually was my camper still it was running off a 20# cylinder. Bottom line it will only cool XX degrees below ambient temps so on a 90+ degree day it maybe only 45* inside at 40 it's likely to freeze things. 

Link to comment
Share on other sites

2 hours ago, Maineah said:

Shade helps a lot it was in the barn and it actually was my camper still it was running off a 20# cylinder. Bottom line it will only cool XX degrees below ambient temps so on a 90+ degree day it maybe only 45* inside at 40 it's likely to freeze things. 

Word. Thanks. I will keep that in mind.

Link to comment
Share on other sites

1 hour ago, Derek up North said:

And never opening the door for months helps a lot too!

Ha! Makes sense, but makes it tricky to use.

Link to comment
Share on other sites

There are some more components to a happy refer. 1: a ventilation fan mounted at the highest vent, the idea is to get air flow through the back coils. There are some solar fan options. You want to suck the air from the bottom to the top and out the vent
2: Pre-cool the refer with some frozen water bottles in both the freezer and the main compartments. Leave them in for your trip if you can. 3: Thermal mass. These refers work with thermal mass. Pre-cool everything your going to put in it. If it is empty when you open the door all the cold air dumps out, replaced with warm air. 4: Leveling. Don't use the inside of the refer to check if you are level. Pre-level and place some bubble levels somewhere for easy checking. 5: Get a temp monitor made for these refers. They end some of the guessing. 6: Plan your trips into the refer. Get everything once, opening and closing the door several times while preparing meals is tuff to recover from. 7: Gas vs Electric. The electric heating element is mounted directly to the tube that needs to be heated. The gas is different in that the heat from the flame travels up through the chimney through a spiral baffle. That spiral baffle can eventually start to decay to the point where it becomes harder and harder to transfer the flames heat. If you are finding a bunch of rusty debris below the chimney then the baffle is dying. That disintegrating baffle is one reason an older refer has cooling problems. 8: It is also possible that a previous owner ran the refer too far out of level too many times and some of the cooling mixture has solidified in the internals. 

Link to comment
Share on other sites

8 hours ago, Gulfstream Greg said:

There are some more components to a happy refer. 1: a ventilation fan mounted at the highest vent, the idea is to get air flow through the back coils. There are some solar fan options. You want to suck the air from the bottom to the top and out the vent
2: Pre-cool the refer with some frozen water bottles in both the freezer and the main compartments. Leave them in for your trip if you can. 3: Thermal mass. These refers work with thermal mass. Pre-cool everything your going to put in it. If it is empty when you open the door all the cold air dumps out, replaced with warm air. 4: Leveling. Don't use the inside of the refer to check if you are level. Pre-level and place some bubble levels somewhere for easy checking. 5: Get a temp monitor made for these refers. They end some of the guessing. 6: Plan your trips into the refer. Get everything once, opening and closing the door several times while preparing meals is tuff to recover from. 7: Gas vs Electric. The electric heating element is mounted directly to the tube that needs to be heated. The gas is different in that the heat from the flame travels up through the chimney through a spiral baffle. That spiral baffle can eventually start to decay to the point where it becomes harder and harder to transfer the flames heat. If you are finding a bunch of rusty debris below the chimney then the baffle is dying. That disintegrating baffle is one reason an older refer has cooling problems. 8: It is also possible that a previous owner ran the refer too far out of level too many times and some of the cooling mixture has solidified in the internals. 

Many thanks. I'm getting a great picture now on how to use this fridge most efficiently. Cheers!

Link to comment
Share on other sites

11 hours ago, BBC3 said:

components to a happy refer

These are all excellent points.  

Leveling is essential for these units.  About +/- 2 degrees I'm told is where you need to be.  I've been lazy and parked for a hike or whatever and found the fridge warmed up.  It recovers ok but takes some time to catch up.  It is a tedious aspect of these units for sure but no way around it.  I put the Ride-rite air bag controller/pump in my rig and I use it a lot to get the rig level enough each time I park.  I took some time and carefully mounted some Hopkins 08525 graduated level indicators because I got tired of trying to find the right spot for the bubble indicator (yes, bottom of fridge is not all that flat so it's not a good place to monitor from).

A temperature monitor is a great idea.  That will give me a much better idea of how things are working.

Using an ice mass in the fridge is another good tip.  It's like a cold buffer.  I'll try this out.  I keep two plastic bins in the lower section of the fridge and keep most food in these hard top containers.  At mealtime I open the door and take both containers out and close the door. I sort though them and get what I need and then put the two bins back in one swift move.  I think this helps minimize the time the door spends open.

I also use a fan mounted to the top fins to move air through the back. I have it going through a temperature switch so it only goes on when the back fin area is above about 90F.  The solar fan is a good idea too!

I'm going to throw out one other thing to be aware of, although hopefully nobody will ever experience it first hand: the dreaded ammonia smell.  If you open your fridge and smell ammonia then you need to address it.  Almost certainly this means you have a leak in the inside coils.  It's harder to notice from the outside but if you detect a faint ammonia smell you should take it seriously.  I was fortunate enough to have this wonderful experience and this meant that my cooling section had to be replaced.  I bought the "Amish built" refurb unit you can find on ebay for my Dometic RM2401 and it was $415 after I sent back the core.  Install was pretty straight forward and quality and customer service is excellent.  The replacement works great and I have had zero issues with it.  I recommend this refub option as it's a lot less than a new fridge.

 

Link to comment
Share on other sites

On 6/4/2019 at 5:33 AM, AtlantaCamper said:

I took some time and carefully mounted some Hopkins 08525 graduated level indicators because I got tired of trying to find the right spot for the bubble indicator (yes, bottom of fridge is not all that flat so it's not a good place to monitor from).

Use the freezer tray for the initial leveling. Find a flat parking area. Get it exact then place your levels. Two inside the coach and two inside the cab. When parking get it close with the cab levels then check the coach levels. The cab and coach will not always read the same due to some twisting of the cab and frame on uneven terrain. We had a refer in one rig that really needed to be almost perfect to be happy. I think it had a ruff life before we got the rig. Everyone's refer will cool differently depending on it's history. I have met many who had no clue the refer needed to be level.

Link to comment
Share on other sites

  • 3 weeks later...
On 6/3/2019 at 11:46 AM, Gulfstream Greg said:

components to a happy refer:  Pre-cool the refer with some frozen water bottles

I was interested in trying out this tip, plus I wanted to see how much adding air circulation fans inside the fridge would improve overall efficiency, in particular during start-up.  I'm pleased to report that ice packs and fans can significantly reduce the start-up time for an RV fridge!

This is going to be a long post so here is the executive summary take-home info:

  • The combination of ice-packs and internal fans reduced the "start-up time" (time to reach stable, cold operational temps) from 12+ hours to 4.5 hours.
  • The ice-packs had a more significant impact on reducing 'start-up time' than the fans but the fans improved heat transfer to a room temp beer that was put in the fridge during start-up.
  • Ice blocks/packs are the simplest way to reduce start-up time (no wiring).  Ice blocks alone could reduce start-up time by about 40%.
  • Ice packs in the freezer do not impact the main fridge compartment. Freezer and fridge fins are only weakly thermally coupled.  Put the bulk, if not all, of the ice-packs in the fridge. 

Based on my tests I have adopted a fridge start-up routine that will allow me to start the fridge the same day I'm leaving (I'm always forgetting to do it the night before).  I'll put the ice packs in, turn on the fridge and fan.  After 4 or 5 hours I'll put the pre-cooled contents in.  At that time or maybe a few hours later I'll remove the ice packs and put them in the cooler that I use for drinks and keep in the base of the shower.  I find that using the cooler in parallel with the fridge is most effective for my family but YMMV.

These are the items I purchased, some fans and ice-packs:  

  1. Two small Sunon 50 mm Fans - model KDE1205PHV3 fans for $12.95 on ebay https://www.ebay.com/itm/2-X-Sunon-50-mm-Ultra-Quiet-Cooling-Fans-12-V-10-CFM-22-dB-KDE1205PHV3/280833965042  The pair uses less than 0.1 amps and moves a decent amount of air.  That's a low enough power draw that I don't mind them being on all the time.
  2. Cooler Shock: $22.50 for three re-usable ice-packs that are the equivalent of 18 pounds of ice but weigh only 12#.  https://www.amazon.com/gp/product/B00V9ITMYC  These ice-packs are sized nicely to fit in the freezer or on the wire rack shelf (see pic below).  A (free) DIY ice-bottle would certainly be an effective substitute.

Ice packs: IMG_20190627_201912.jpg.fae6d5a5c716763794f2cfd06f781a06.jpg

Fans:IMG_20190627_201554.jpg.6371140d768299f92e114c1888b1cbb4.jpg  IMG_20190627_201407.jpg.448d6226e66be3470c56aefe2db2cb9a.jpg

The fans are mounted under the fins blowing up.  I was able to thread a power wire into the same hole where the thermometer feeds in and wired to an external switch.

There were three variables tested during repeated start-ups from ambient temps: 1) reefer on or off, 2) ice-pack in the fridge or not and 3) fans on or off.

This is a graph comparing the start-up cooling effectiveness after 4.5 hours.  Taller bars are better:

1730696120_fridgetest.JPG.f37b896e7160be57915631d32e266580.JPG

Interestingly, ice by itself was almost as effective as the reefer alone over 4.5 hours.  It takes the ammonia fridge process a while to get going but the ice starts cooling right away.

One interesting thing I discovered is that the freezer section is not thermally coupled to the coils in the main fridge compartment.  I put the ice-packs in the freezer and the cold does not migrate to the fins in the main fridge compartment.  While you can put an ice pack in the freezer, the fridge is the section that is slowest to come down to operational temps so I'd suggest putting all the ice packs there.  

I would suspect that bottles of frozen water would work well instead of these fancy-pants ice-packs, so you can get a major boost in start-up efficiency for free by just putting an ice mass in the fridge when you start the reefer.  

All of these tests were focused only on start-up.  I have not tested how the ice-packs impact the actual operational efficiency of the fridge.  Presumably they would act as a 'cold buffer' and help the fridge recover more quickly from door openings or putting warm food items in the fridge, but they do take up a good bit of room.  I did do one test along these lines by putting a room temp beer in the fridge during the start up tests to see how fast it cooled compared to the fins and fridge walls.  The beer lagged behind the fridge wall temperature with the fans off, but with the fans on the beer cooled at the same rate as the walls.    While the fan impact on start-up was not all that huge, I think it's going to be valuable to move the air during normal operation.  It's worth the 0.1 amps I think.

Link to comment
Share on other sites

20 minutes ago, AtlantaCamper said:

I was interested in trying out this tip, plus I wanted to see how much adding air circulation fans inside the fridge would improve overall efficiency, in particular during start-up.  I'm pleased to report that ice packs and fans can significantly reduce the start-up time for an RV fridge!

This is going to be a long post so here is the executive summary take-home info:

  • The combination of ice-packs and internal fans reduced the "start-up time" (time to reach stable, cold operational temps) from 12+ hours to 4.5 hours.
  • The ice-packs had a more significant impact on reducing 'start-up time' than the fans but the fans improved heat transfer to a room temp beer that was put in the fridge during start-up.
  • Ice blocks/packs are the simplest way to reduce start-up time (no wiring).  Ice blocks alone could reduce start-up time by about 40%.
  • Ice packs in the freezer do not impact the main fridge compartment. Freezer and fridge fins are only weakly thermally coupled.  Put the bulk, if not all, of the ice-packs in the fridge. 

Based on my tests I have adopted a fridge start-up routine that will allow me to start the fridge the same day I'm leaving (I'm always forgetting to do it the night before).  I'll put the ice packs in, turn on the fridge and fan.  After 4 or 5 hours I'll put the pre-cooled contents in.  At that time or maybe a few hours later I'll remove the ice packs and put them in the cooler that I use for drinks and keep in the base of the shower.  I find that using the cooler in parallel with the fridge is most effective for my family but YMMV.

These are the items I purchased, some fans and ice-packs:  

  1. Two small Sunon 50 mm Fans - model KDE1205PHV3 fans for $12.95 on ebay https://www.ebay.com/itm/2-X-Sunon-50-mm-Ultra-Quiet-Cooling-Fans-12-V-10-CFM-22-dB-KDE1205PHV3/280833965042  The pair uses less than 0.1 amps and moves a decent amount of air.  That's a low enough power draw that I don't mind them being on all the time.
  2. Cooler Shock: $22.50 for three re-usable ice-packs that are the equivalent of 18 pounds of ice but weigh only 12#.  https://www.amazon.com/gp/product/B00V9ITMYC  These ice-packs are sized nicely to fit in the freezer or on the wire rack shelf (see pic below).  A (free) DIY ice-bottle would certainly be an effective substitute.

Ice packs: IMG_20190627_201912.jpg.fae6d5a5c716763794f2cfd06f781a06.jpg

Fans:IMG_20190627_201554.jpg.6371140d768299f92e114c1888b1cbb4.jpg  IMG_20190627_201407.jpg.448d6226e66be3470c56aefe2db2cb9a.jpg

The fans are mounted under the fins blowing up.  I was able to thread a power wire into the same hole where the thermometer feeds in and wired to an external switch.

There were three variables tested during repeated start-ups from ambient temps: 1) reefer on or off, 2) ice-pack in the fridge or not and 3) fans on or off.

This is a graph comparing the start-up cooling effectiveness after 4.5 hours.  Taller bars are better:

1730696120_fridgetest.JPG.f37b896e7160be57915631d32e266580.JPG

Interestingly, ice by itself was almost as effective as the reefer alone over 4.5 hours.  It takes the ammonia fridge process a while to get going but the ice starts cooling right away.

One interesting thing I discovered is that the freezer section is not thermally coupled to the coils in the main fridge compartment.  I put the ice-packs in the freezer and the cold does not migrate to the fins in the main fridge compartment.  While you can put an ice pack in the freezer, the fridge is the section that is slowest to come down to operational temps so I'd suggest putting all the ice packs there.  

I would suspect that bottles of frozen water would work well instead of these fancy-pants ice-packs, so you can get a major boost in start-up efficiency for free by just putting an ice mass in the fridge when you start the reefer.  

All of these tests were focused only on start-up.  I have not tested how the ice-packs impact the actual operational efficiency of the fridge.  Presumably they would act as a 'cold buffer' and help the fridge recover more quickly from door openings or putting warm food items in the fridge, but they do take up a good bit of room.  I did do one test along these lines by putting a room temp beer in the fridge during the start up tests to see how fast it cooled compared to the fins and fridge walls.  The beer lagged behind the fridge wall temperature with the fans off, but with the fans on the beer cooled at the same rate as the walls.    While the fan impact on start-up was not all that huge, I think it's going to be valuable to move the air during normal operation.  It's worth the 0.1 amps I think.

nice write up, nice research, thanks! 

Link to comment
Share on other sites

A fan inside, a couple of fans moving hot air out from the rear fins, extra foam insulation. All this makes the ultimate RV refer.  Anything you do makes things better than stock.

Link to comment
Share on other sites

  • 2 weeks later...
On 6/27/2019 at 10:58 PM, AtlantaCamper said:

I was interested in trying out this tip, plus I wanted to see how much adding air circulation fans inside the fridge would improve overall efficiency, in particular during start-up.  I'm pleased to report that ice packs and fans can significantly reduce the start-up time for an RV fridge!

This is going to be a long post so here is the executive summary take-home info:

  • The combination of ice-packs and internal fans reduced the "start-up time" (time to reach stable, cold operational temps) from 12+ hours to 4.5 hours.
  • The ice-packs had a more significant impact on reducing 'start-up time' than the fans but the fans improved heat transfer to a room temp beer that was put in the fridge during start-up.
  • Ice blocks/packs are the simplest way to reduce start-up time (no wiring).  Ice blocks alone could reduce start-up time by about 40%.
  • Ice packs in the freezer do not impact the main fridge compartment. Freezer and fridge fins are only weakly thermally coupled.  Put the bulk, if not all, of the ice-packs in the fridge. 

Based on my tests I have adopted a fridge start-up routine that will allow me to start the fridge the same day I'm leaving (I'm always forgetting to do it the night before).  I'll put the ice packs in, turn on the fridge and fan.  After 4 or 5 hours I'll put the pre-cooled contents in.  At that time or maybe a few hours later I'll remove the ice packs and put them in the cooler that I use for drinks and keep in the base of the shower.  I find that using the cooler in parallel with the fridge is most effective for my family but YMMV.

These are the items I purchased, some fans and ice-packs:  

  1. Two small Sunon 50 mm Fans - model KDE1205PHV3 fans for $12.95 on ebay https://www.ebay.com/itm/2-X-Sunon-50-mm-Ultra-Quiet-Cooling-Fans-12-V-10-CFM-22-dB-KDE1205PHV3/280833965042  The pair uses less than 0.1 amps and moves a decent amount of air.  That's a low enough power draw that I don't mind them being on all the time.
  2. Cooler Shock: $22.50 for three re-usable ice-packs that are the equivalent of 18 pounds of ice but weigh only 12#.  https://www.amazon.com/gp/product/B00V9ITMYC  These ice-packs are sized nicely to fit in the freezer or on the wire rack shelf (see pic below).  A (free) DIY ice-bottle would certainly be an effective substitute.

Ice packs: IMG_20190627_201912.jpg.fae6d5a5c716763794f2cfd06f781a06.jpg

Fans:IMG_20190627_201554.jpg.6371140d768299f92e114c1888b1cbb4.jpg  IMG_20190627_201407.jpg.448d6226e66be3470c56aefe2db2cb9a.jpg

The fans are mounted under the fins blowing up.  I was able to thread a power wire into the same hole where the thermometer feeds in and wired to an external switch.

There were three variables tested during repeated start-ups from ambient temps: 1) reefer on or off, 2) ice-pack in the fridge or not and 3) fans on or off.

This is a graph comparing the start-up cooling effectiveness after 4.5 hours.  Taller bars are better:

1730696120_fridgetest.JPG.f37b896e7160be57915631d32e266580.JPG

Interestingly, ice by itself was almost as effective as the reefer alone over 4.5 hours.  It takes the ammonia fridge process a while to get going but the ice starts cooling right away.

One interesting thing I discovered is that the freezer section is not thermally coupled to the coils in the main fridge compartment.  I put the ice-packs in the freezer and the cold does not migrate to the fins in the main fridge compartment.  While you can put an ice pack in the freezer, the fridge is the section that is slowest to come down to operational temps so I'd suggest putting all the ice packs there.  

I would suspect that bottles of frozen water would work well instead of these fancy-pants ice-packs, so you can get a major boost in start-up efficiency for free by just putting an ice mass in the fridge when you start the reefer.  

All of these tests were focused only on start-up.  I have not tested how the ice-packs impact the actual operational efficiency of the fridge.  Presumably they would act as a 'cold buffer' and help the fridge recover more quickly from door openings or putting warm food items in the fridge, but they do take up a good bit of room.  I did do one test along these lines by putting a room temp beer in the fridge during the start up tests to see how fast it cooled compared to the fins and fridge walls.  The beer lagged behind the fridge wall temperature with the fans off, but with the fans on the beer cooled at the same rate as the walls.    While the fan impact on start-up was not all that huge, I think it's going to be valuable to move the air during normal operation.  It's worth the 0.1 amps I think.

WOW!! 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...