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Topic: Thermal shut off for refrigerator fans (Read 1008 times) previous topic - next topic

Thermal shut off for refrigerator fans

I have two Valterra refrigerator fans (RV Valterra Fridgecool Universal Vent Fan) intalled on top of the heat exchanger of our Dometic refrigerator.  These really seem to help our refrigerator cope with high ambient temperatures, but I worry about what would happen if we had a refrigerator fire.  Would they make it worse?

I'd like to find a way of turning the fans off if a fire started.  It occurred to me that I could use an Atwood thermal cutoff that is used to shut off a gas water heater in case of a fire.  They "blow" at 190 degrees.  Does anyone think this is a bad idea and if so, why?  Any other solutions to this potential problem?

Thanks in advance.
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George Hatfield

  Never ever use World Line Motors of Nacogdoches for service!

Re: Thermal shut off for refrigerator fans

Reply #1 –
George, If you have a reefer fire while it is on gas it will probably not make any difference if you have fans behind it or not.  Once the ammonia begins to escape and the hydrogen hits a flame source its all over.  Most of the reefer failures I have seen that did not result in a fire simply released the ammonia mix resulting in a bad smell only.
Gary B

Re: Thermal shut off for refrigerator fans

Reply #2 –
I had the really strong ammonia smell when my refrig went out on my 89, and luckily called someone who advised shut off reefer and propane STAT!

Tried to take it apart and order new coil, but once I had it apart CW had a big sale on an exact fit - so I replaced.

Not this bad boy in the 2000 U-320, residential for me in the spring....
Tim Fiedler    2025 LTV Unity MBL on Order
2000 Chevy Tracker 2 Door Convertible 4WD Now lifted 4.5"
1985 Citroen 2CV6 Charleston
Murphy Rebel on wheels with 175HP Titan
Cessna P337
1980 48' Westport MY (!/4 Share)

Re: Thermal shut off for refrigerator fans

Reply #3 –
Quote from: George Hatfield –
I have two Valterra refrigerator fans (RV Valterra Fridgecool Universal Vent Fan) intalled on top of the heat exchanger of our Dometic refrigerator.  These really seem to help our refrigerator cope with high ambient temperatures, but I worry about what would happen if we had a refrigerator fire.  Would they make it worse?

I'd like to find a way of turning the fans off if a fire started.  It occurred to me that I could use an Atwood thermal cutoff that is used to shut off a gas water heater in case of a fire.  They "blow" at 190 degrees.  Does anyone think this is a bad idea and if so, why?  Any other solutions to this potential problem?

Thanks in advance.
Those fans should already be tied into a button thermostat at the top of the fins. It turns "ON" the fans when the temp gets to the thermostat setting. Adding another thermostat to shut it off would defeat the purpose.
The selected media item is not currently available.Barry BEAM #16014
2003 U320 40' AGDS
Beamalarm, Foretravel technical help and specifications
"Whatever the mind can conceive and believe, it can achieve"

Re: Thermal shut off for refrigerator fans

Reply #4 –
Thermal fuses are available for several temperatures. Radio Shack or an appliance parts store would have them. I've replaced thermal fuses in a water heater, an "instant hot water" dispenser, and an electric iron.

I don't have expertise to know if it would be a good idea to install a thermal fuse in your application.

I did have a cooling unit fail while operating on propane. There was no fire. There was a strong ammonia smell. The rupture of the system appeared to be near the flame. That is where there was a telltale yellow residue. I replaced the cooling unit because it was relatively easy to do and the cost was comparable to replacement with a residential unit. It has performed to our satisfaction in outside temperatures ranging from 0 to 110F.
J D Stevens
1997 U295 CAI 36' Build #5085
2002 Subaru Outback
Motorcade 16869
Bellville, TX

Re: Thermal shut off for refrigerator fans

Reply #5 –
My guess, in case of fire the heat will immediately destroy (melt?) the fans. An over temp switch would be overkill, literally.
Tom Lang K6PG (originally  KC6UEC)
and Diane Lang
2003 38 U295 build 6209
2016 Jeep Grand Cherokee Summit Ecodiesel
still have tow-ready 2006 Acura MDX 
Temple City, California
Motorcade 16681 California Chapter President
SKP 16663 member of SKP Park of the Sierra, Coarsegold California
FMCA F071251
Retired electrical and electronic engineer

Re: Thermal shut off for refrigerator fans

Reply #6 –

George,

What a great idea to use the Atwood propane water heater thermal cutoff fuse on your fans.

We like those fuses and maybe they could also be used by AquaHot near the burners.

They are cheap and come two to a package.
Atwood 93866 Thermal Cut Off Kit, (Pack of 2) : Amazon.com : Automotive

As an Amazon Associate Foretravel Owners' Forum earns from qualifying purchases.

Re: Thermal shut off for refrigerator fans

Reply #7 –
If you have had the Dumetic recall done with the new metal flashing and high limit thermostat, you could tie the fans into the high limit, when and if something went wrong it would shut down the entire unit.
The selected media item is not currently available.Bill&Doris 97 U270 36'
University of Parris Island Class of 66
Semper Fi  Build# 5174 MC#17094

Re: Thermal shut off for refrigerator fans

Reply #8 –
I have a related question to the one I posed to start this thread.  The Valterra fans I installed about a year ago have again failed.  That is the second pair that have failed, each lasting about a year.  I'd like to use some muffin fans as a replacement this time around.  As described previously, I installed these on top of the refrigerator heat exchanger up on the roof.  The trick is finding fans that will take the heat of being so close to the heat exchanger.  They don't actually sit on the coils, but are about an inch away so they will get hot.  I have found some muffin fans in Tucson that can operate up to 80 degrees C (about 180 degrees F).  Sound good enough?  Does anyone know of a source of muffin fans that will take more heat?  Thanks in advance.

By the way, when I talked to "Mac the fireguy" here in Tucson (FMCA rally) and he didn't seem to think that any sort of fan cut off switch would be needed in case of a fire if I used one of his Halon units.  I did buy one and posted the picture of the installation earlier. 

George
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George Hatfield

  Never ever use World Line Motors of Nacogdoches for service!

Re: Thermal shut off for refrigerator fans

Reply #9 –
We run our behind fridge fans from the bottom blowing up. Fans are just above the side vent and work just fine.

Re: Thermal shut off for refrigerator fans

Reply #10 –
I found a "cartoon" on how absorption refrigerators work on the web.  It was produced by Dometic in GIF format and although the file size was small, it was difficult to watch due to the relatively short delay between the frames and because the animation could not be paused.  So I fixed it (I think).  See the link below.  This is an AVI file that can be played on most computers.  There is no sound track.  And it can be paused if you want to think about a point before going on.

How absorption refrigerator works on Vimeo

For those that cannot download this file, a modified GIF is attached.  This one has longer delays before frame changes, but cannot be paused.

For once I think I understand how these units work.  Now I see why one smells ammonia before the hydrogen escapes to cause a fire.  And that the purpose of those fins on top is to condense the ammonia to liquid which is essential to it acting as a refrigerant. 

George
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George Hatfield

  Never ever use World Line Motors of Nacogdoches for service!

Re: Thermal shut off for refrigerator fans

Reply #11 –
As I have mentioned before the Valterra fans designed to provide extra cooling the the condensor coil of absorption refrigerators don't last very long.  I have installed two pairs and all have failed within a year. 

Here is a cheap substitute.  80mm muffin fans easily fit into the housing for the Valterra fans.  All that is required is to file the corners a bit and you have a tight fit.  I also removed the cross support for the old fan motors.  As shown in the attached photo, I  put in a coupe of "set" screws to secure them and used epoxy to further secure them at each corner on the bottom.  I got these fans from a friend... they came from an old Xantrax inverter, but these fans are readily available elsewhere for under $10.  Lets see how long these last.  New Valterra fans cost about $40 each.  The ducts not only make the fans easy to install, but also make the fans more efficient.
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George Hatfield

  Never ever use World Line Motors of Nacogdoches for service!

Re: Thermal shut off for refrigerator fans

Reply #12 –
I installed the reworked fans and they seem to move quite a bit of air.  They are a little noisier than the Valterras, but not overly so.  Easy to hear they are running from the outside of the coach.  Rather than remove the roof vent, I just cut away the plastic screen and replaced it with metal screen. 
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George Hatfield

  Never ever use World Line Motors of Nacogdoches for service!