Be sure to sign up for the weekly RV Travel Newsletter, published continuously every Saturday since 2001. Click here.

Thursday, July 12, 2012

Do You Like Your Drinks COLD? - Installing a Fridge Chimney Fan.


Not Quite Cold Enough
    On my last trip it was over 90 degrees out (Farenheit, if it were Celsius I'd be cooked!)  I love cold drinks, the colder the better. My RV fridge was struggling to maintain 48 degrees in the fridge compartment and the freezer was edging up past 20 degrees. Mostly because I was parked, the only way I could, with the wall where the fridge was is in direct sun most of the day. I had looked into a supplemental fan, mounted in the chimney, below the roof exhaust vent last year. Now I knew I had to install one. This isn't really difficult to do, but can really make a difference in hot weather

120MM 12 Volt "Muffin" Fan
All RV absorption fridges use convection to transfer heat up and away from the interior. It's really an elegant way of making cold from heat. The manufacturer will set specifications that show the space needed around the fridge during an install. On mine, the space behind the fridge is quite large, so a fan will help create an air current to move the hot air up and out the existing roof vent.

To get the air moving I used a computer style "muffin" fan. It's about 4" across and draws around 1/2 Amp at full speed. These are commonly available online and from local retailers. They aren't expensive at all. Mine was 7 dollars including shipping. I thought I would need some kind of bracket, but my 1"+ roof plywood and the small holes in the corner of the fan surround were sufficient to mount the fan above the fins and below the vent.

Roof Vent Off (Wires are from Solar Panels)
Shut off the fridge! Gather all the tools you think you'll need. I'm sure (like me) you will be going up and down the ladder a whole bunch of times to get things you forgot. Better yet, get someone to help!
Next remove the screws holding the fridge vent on. Remove the vent and put it aside. Preferably somewhere it won't fall off the roof. Remove (carefully!) the mesh vent cover. These are designed to keep critters out. Do they really work? It will bend easily so put it aside.You may also have a thin  metal plate above the cooling unit. This is a baffle to re-direct the airflow up and out. Mine was bent everywhere! I straightened it as best I could and made sure the air path to the vent was clear.

Now we figure out where you want to locate the fan.

Close Up of Opening Showing Cooling Fins
Look closely inside the vent opening. Do you see the cooling unit for the fridge? It's the metal tubing with square fins surrounding it. The top is where heat is removed from the system.

 I put mine mostly over the fins on the cooling unit. I figure drawing air up through the chimney and across the fans will increase efficiency.

  MAKE SURE THE FAN EXHAUSTS UP!!!

Otherwise, you'll have to flip it over and start the mounting procedure again.


Fan Mounted, Wiring Done, Zip Tied, With Heat Shrink Tubing! 
I had some 2 conductor wire left over from another install. It was 20AWG...more than sufficient for a 1/2 Amp draw. I spliced this onto the fans "pigtails" and covered the splice with heat shrink tubing to make it more water resistant. (You thought I would forget that AGAIN, didn't you?Next I zip tied the splices and some wire to a convenient spot to avoid pulling on them when they were wired down below. Drop the wire in the chimney away from the cooling unit as best you can.

Climb down. (Again?)

Lower Fridge Vent Compartment.
Once back on the ground, open your lower fridge vent and make sure it isn't going to fall on you (over and over, bashing you on the head.) Find the 12 Volt ground and the Power block for the fridge. A cheap multi-meter that reads volts will be VERY helpful here, but you could just look at the diagram that MAY be attached to the plate covering the fridges innards. Attach the ground. I used the plate at the bottom of the fridge. There were quite a few wires using this as a ground already so I simply crimped on a ring style terminal and used an existing screw.


Giant Mystery Switch (Now Fan Control)
For the positive 12 volt line, I could have used the main power into the fridge or found a line from the fridge control board. If you use the one on the control board make sure it can supply the amperage you need. In either case install a fuse!! The control board method will turn on power to the fan every time the fridge is on. Not ideal.

Since I bought my RV there has been this HUGE toggle switch in the lower fridge vent that I couldn't figure out what it was for. Now I know. It was put there for me to attach the fridge fan power lead. OK, so I really have NO idea what it was for, but it works nicely for this application. After testing this for a while in the heat, I will likely hard wire power to the fridges main power block and out to a switch INSIDE to control the fan. You could buy a thermostatic switch to turn the fan on and off with temperature, but that's another article. For now, manual control is OK for me.

With a single day of testing, it appears that I have gone from 44.9 degrees down to 35.6 degrees in the main  fridge compartment, in the same outside conditions. The freezer is also down to 1 degree. I have the fridge set to a lower number on its control panel as well. It's set to 4 instead of 5. Only more testing will confirm the true value of this upgrade, but for now...I'm happy.

Be Seeing You...Down The Road,

Rich "The Wanderman"
www.thewanderman.com


18 comments:

  1. I did something similar, but to a far greater extreme.

    First, I got a guide on how far from the wall an RV Fridge's coils should be, I believe the max gap between the coils and the walls should be no greater than 1", otherwise, convection occurs outside the coils and prevents the proper air movement through the coils and the fins on top.

    To fix this, I built out my wall using 1x2s and FRP board so that the coils were closer to the wall to prevent air bypass.

    Second, I built a sheet metal duct that went from the top of the fridge's back up to the vent on the roof so that all heat was directed out vs into the dead space around the fridge.

    Third, I filled all the dead space in with faced fiberglass insulation to give the nearly 40 year old fridge a good 4" or greater insulation jacket on all the sides but the back where the cooling unit is.

    Fourth, when I built my duct, I installed a bank of 4 80mm fans a half an inch above the cooling fins on the top so that they would draw air through the fins and exhaust it out the top, causing a proper draft induction to occur.

    Fifth, I installed as set of two more of these 80mm fans inside my fridge directly centered on my cooling fins that pull air over the fins and exhaust it towards the door, causing a proper circulation pattern to form.

    My fridge stays in the high 20s and low 30s in 90 or hotter weather on it's lowest setting now.

    ReplyDelete
    Replies
    1. Matt,
      Wow! That's a lot of work. Probably would have been better if the manufacturer had just installed it correctly the first time. Adding insulation is a GREAT idea! I will look into that on my fridge compartment as well.

      Any idea how much power all those fans pull?? Are they noisy?

      Thanks,

      Rich "The Wanderman"

      Delete
    2. The fans draw 0.12 amps each for a grand total of 0.72 amps, not enough to worry about Ah wise.

      There a very dull sound when they're running, barely noticable above the background noise.

      My fridge is the factory original, all mechanical. She's been running strong since 1974, but couldn't combat 100 degree temps till I did my improvements, now I never have to turn her up.

      Delete
    3. Matt,
      Hmmm...the fan I installed is rather noisy. Not horrible, but I can hear it inside if nothing else is running. On full blast it draw a little less than .5 AMP. What kind of fans did you use???

      These fridges SHOULD run forever if properly maintained.

      Rich "The Wanderman"

      Delete
    4. The units I bought were branded as being super quiet and have been pretty much that, though I also keep a Shurflo Comfort Breeze running alot of the year (With the lid shut during the winter to mix the air and open to draw air through the rig in the summer).

      Delete
    5. Matt,
      I saw a really nice 4 92mm fan pack, mounted on an nice aluminum frame with a mounting flange on one side (exactly what I need) However, it's 420MM wide and that would effectively block the whole vent opening. I am toying with the idea of cutting it in half..

      Rich "The Wanderman"

      Delete
  2. I have done a similar thing attaching the hot lead to the solar line. Sun shines, fan runs. Moon shines, fan is off. Never have to think about it.
    Thanks for sharing.
    Dan

    ReplyDelete
    Replies
    1. Dan,
      Good idea! My panels are 48Volt nominal, so the direct approach is out. Since I am charging the batteries with the solar array all day..I'll likely just tap into the existing 12V line and put in a thermo switch and a manual cutoff.

      Thanks,

      Rich "the Wanderman"

      Delete
  3. Rich, If you want less noise you can use two 12 volt fans side by side and wire them in series or use two 24 volt fans and wire them in parallel and they will run slower and quieter, but still move considerably more air past the fins than without. They will also use much less current this way. Jeff

    ReplyDelete
    Replies
    1. Jeff,
      OK..that sounds reasonable to me. After I finish testing the single 120MM fan and it's airflow and effects on cooling I will tackle making the assembly quieter!

      Thanks,

      Rich "The Wanderman"

      Delete
  4. Gentlemen,
    I have a 2009 Safari Cheetah (by Monaco)that had two fans installed in a baffle below the coils in the back.
    There is a thermostat located on one of the fins at the top that is supposed to turn the fans on when the space reaches 150 degrees F (verified by testing and with Monaco).
    The space apparently never got quite that hot so the fans never ran even though the wooden interior wall next to fridge was very hot to the touch.
    Last fall I wired a switch in parallel with the thermostat and installed it inside the coach. It has a red LED that lights to remind me that the switch is on and the fans are running. If the thermostat were to turn the fans on the LED would also light. I plan to replace the thermostat with one rated at ~ 130 degree F because I think 150 degrees is way too hot. I had to do this becaues the fridge is in a slide out and the top vent is in the side instead of the roof of the coach. My fridge now stays at 36 degrees with the control set on 4 where before it was in the low 40s on a hot day no matter what setting the control was on.

    ReplyDelete
    Replies
    1. Anon,
      Another success story! I have no idea why manufacturers don't simply update their designs and/or install these fans from new???

      Rich "The Wanderman"

      Delete
    2. Most of the thermostat's I've seen used were set to turn on at around 85 or higher to start removing heat before it built up too much.

      Mine draw so little power that I just turned them on and left them on.

      I'm finally replacing the two inside the fridge after they've been running for over 6 years and while they still work have started to make alot of noise from all that time in a moist environment.

      Delete
    3. Matt,
      I've toyed with the idea of a thermostat, but I am so crazy about monitoring, I may just have a manual switch inside. Of course, I COULD do both....

      Rich "The Wanderman"

      Delete
    4. a single pole 2-way switch would be perfect, flipped one-way, manual operation, flipped the other, the thermostat is now in the circuit.

      Delete
    5. Matt,
      EXCELLENT IDEA! I just scored a bunch of various switch types that match the dashboard ones. I have a whole box of them. Now to find a thermostatic switch I can set AND figure out where to mount it so it reads a true temperature in the chimney.

      Rich "The Wanderman"

      Delete
    6. Most of the thermostat installations were placed on the wall closest to the cooling fins on the back of the unit where the most heat is generated, and released.

      Delete
    7. Matt,
      OK...Gotcha. I'll do some measuring and look for a sensor. Might as well have one that reads out as well. So i can monitor from inside.

      I did notice that with the fan running the wall panel above the fridge doesn't get hot anymore. Probably needs some additional insulation as well.

      Rich "The Wanderman"

      Delete

Thank you for your comment. Our moderator checks each one to make sure we keep the Spammers away. So the comment will likely not appear immediately.