Forum Discussion

SidecarFlip's avatar
SidecarFlip
Explorer III
May 08, 2017

Ammonia versus Compressor Fridge...

After all the talk about Danfoss compressor fridges and how much better they were than the old school Ammonia Units, I decided to 'fiddle with mine and do a long term test using a remote digital recording thermometer.

First thng I did was open up the rear cavity. My fridge is a side vent, that is, not through the roof, intake low (with plumbing and control board) and the upper vent vertical on the side of the camper at the height of the top of the fridge.

I opened it up and removed the one small 12 volt muffin fan Suburban had installed. It was a cheapo sleeve bearing fan, very noisy. I replaced it with 2 Fluid Dynamic Bearing 120 MMM high flow computer fans (23 bucks, E-bay. Had to make up a set of brackets as I wanted the fans as close to the upper condenser as possible. Suburban has already installed a snap action thermostat (on at 90 off at 70) so I wired both into the existing thermostat.

I also added a lot of R13 unfaced insulation between the fridge and the cabinet. I actually stuffed almost 1/2 roll in. Plenty now.

I also fabricated an upper baffle that fits tight against the back of the upper condenser and screws into the camper side,inside, effectively channeling the air flow with no turbulence as it passes through the condenser.

I took a full 20 pound bottle of propane (valved off my second bottle) and set the fridge on gas only (it is shore powered sitting in the yard.)

So far, it's been running for 3 weeks straight on that bottle, I'm expecting over a month. Amp draw with the fans running is 1.8 amps, with the fans off. .2 amps..Temperature swings (day and night) (and the camper gets the afternoon sun on the fridge side) is 4 degrees.

Last year I had to run the fridge on setting 5 to maintain 40 in the compartment. It't drifting between 33 and 36 inside now..... on setting 2...

I measured the cool down time from ambient as well. It took exactly 3 hours from ambient to 33 degrees.

Still chugging along out there as I post this. When it runs out of propane, I'll post it.

If it ever dies, I'll install a Danfoss unit but for now the old school fridge appears to be doing well.
Truck Campers
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    May 08, 2017
    And just imagine how well that absorption fridge would have cooled from the onset IF (BIG BOLD IF) RV MFG would have taken the time to follow the RV Fridge MFGs 'Installation Instructions'?

    Everything YOU had to do should have been done by RV MFG ------- just google your specific model Installation Manual and you will see 'clearances, baffles, fans' etc ALL diagrammed with Pictures, written instructions and warnings.

    Stupid RV MFGs (cheap, piece-mill culture) cause majority of cooling issues.....by simply NOT following directions
  • Boatycall's avatar
    Boatycall
    Explorer
    May 08, 2017
    SidecarFlip wrote:
    So far, it's been running for 3 weeks straight on that bottle, I'm expecting over a month. Amp draw with the fans running is 1.8 amps, with the fans off. .2 amps.


    Do you have a "Before mods" propane draw down test for comparison on your "After mods"? I'd be very curious to hear the gains.
  • rexlion's avatar
    rexlion
    Explorer
    May 08, 2017
    SidecarFlip wrote:
    After all the talk about Danfoss compressor fridges and how much better they were than the old school Ammonia Units, I decided to 'fiddle with mine and do a long term test...

    Last year I had to run the fridge on setting 5 to maintain 40 in the compartment. It't drifting between 33 and 36 inside now..... on setting 2...

    I measured the cool down time from ambient as well. It took exactly 3 hours from ambient to 33 degrees.....

    I am keying into your previous year data: your fridge could maintain 40 degrees to begin with. I have had ammonia fridges that could not keep 65 degrees on a hot (100 degree) day! You have been lucky.
  • work2much's avatar
    work2much
    Explorer
    May 08, 2017
    Our propane use is way down now after running the stock ammonia fridge quite a bit on 12v. When it dies, I will no doubt replace it with an efficient 110v unit.
  • jmtandem's avatar
    jmtandem
    Explorer II
    May 08, 2017
    After all the talk about Danfoss compressor fridges and how much better they were than the old school Ammonia Units


    I think much of the thinking about compressor refrigerators being better than old school ammonia units regards having to be level, propensity of fire, no need for propane, and basically a home type refer in the RV. And we are all familiar with home units, how long they last and how reliable they are. The compressor's drawback is boondocking where it might be less efficient using limited power unless there is plenty of solar/battery power or generator time daily. I am going compressor next time in any RV I acquire.
  • SCVJeff's avatar
    SCVJeff
    Explorer
    May 08, 2017
    pianotuna wrote:
    You still have to worry about being level.
    No problem there.. I simply fall over that indicates not level :)
  • SidecarFlip's avatar
    SidecarFlip
    Explorer III
    May 08, 2017
    Old-Biscuit wrote:
    And just imagine how well that absorption fridge would have cooled from the onset IF (BIG BOLD IF) RV MFG would have taken the time to follow the RV Fridge MFGs 'Installation Instructions'?

    Everything YOU had to do should have been done by RV MFG ------- just google your specific model Installation Manual and you will see 'clearances, baffles, fans' etc ALL diagrammed with Pictures, written instructions and warnings.

    Stupid RV MFGs (cheap, piece-mill culture) cause majority of cooling issues.....by simply NOT following directions


    I suppose you are correct. I didn't look at any diagrams, just used a common sense approach.

    I had precious little insulation between the fridge unit and the outer cabinet, maybe one layer about halfway between the front and the middle, I was appalled at how little there was. Stuffed now. No easy task getting it in either. I used a wood yard stick and carefully stuffed it in.

    I'm considering an 'in the fridge' distribution fan to increase the cooling exchange rate between the evaporator and the inner compartment as well (maybe one of those battery ones, but at this point I don't see the need.
  • SidecarFlip's avatar
    SidecarFlip
    Explorer III
    May 08, 2017
    pianotuna wrote:
    You still have to worry about being level.


    Fair statement. It is easier to level a TC than say a large TT. I purposely am running out of 'level' by 1/2 bubble on my torpedo level, place on top of the fridge cabinet. I can usually do better when camping but I figured I'd see how it did not quite level, it's fine.
  • SidecarFlip's avatar
    SidecarFlip
    Explorer III
    May 08, 2017
    rexlion wrote:
    SidecarFlip wrote:
    After all the talk about Danfoss compressor fridges and how much better they were than the old school Ammonia Units, I decided to 'fiddle with mine and do a long term test...

    Last year I had to run the fridge on setting 5 to maintain 40 in the compartment. It't drifting between 33 and 36 inside now..... on setting 2...

    I measured the cool down time from ambient as well. It took exactly 3 hours from ambient to 33 degrees.....

    I am keying into your previous year data: your fridge could maintain 40 degrees to begin with. I have had ammonia fridges that could not keep 65 degrees on a hot (100 degree) day! You have been lucky.


    Actually, I don't, other than my first hand experiences last year with getting it to 'cool down' prior to a trip. It always took at least 24 hours to cool off and temperature fluctuation was pretty extreme (I was using a non recording wireless thermometer then. Daytime highs were low 40's nigh lows were mid 30's and that is on maximum setting.

    That is what prompted me to fiddle with it in the first place. I knew it could do better.

    What I don't really know is propane consumption before and now because I don't know if the boiler flame modulates with the thermister or not. I do know when the fridge is at 33, the control board shuts it off entirely and restarts it at 35 because I've observed (listened) to the ignitor, ignite a couple times. I would imagine it's less, but not sure.

    I think 3 weeks straight (now) isn't bad actually, propane is pretty cheap today.

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