Spillover Fan - suck or blow?

[sailorboy1]

I think my spillover fan is installed backwards (probably something I did once when checking the fan). While it is hard to tell with the system running I think my spillover fan is blowing air into the freezer from the refrigerator as ice really builds up on the freezer side. I think it probably should be sucking air out of the freezer and blowing it into the frig side.

What is the group say?

[onestepcsy37]

Yes. Freezer to fridge, assuming the cold plate or evaporator is in the freezer compartment, where it should be.

[colemj]

Operationally, it really doesn't matter which way the fan goes. As for ice buildup, blowing from freezer to fridge will just cause the buildup to occur at the exchange hole side - where the air necessarily goes from fridge to freezer. It is a closed system.

Sometimes, fans mounted to blow air from freezer to fridge suffer freeze problems and stop working or work slowly. Turning it around prevents that because it never sees temps below freezing.

Mark

[sailorboy1]

I wonder if something like a small sheet of Teflon mount on the plate across from the spillover wall holes would prevent ice blockage.

[colemj]

Originally Posted by sailorboy1

I wonder if something like a small sheet of Teflon mount on the plate across from the spillover wall holes would prevent ice blockage.

That is what we do, except I just cut up a plastic milk jug. Teflon sheet is for Hunter 50's and their high-falutin' ilk.

Cut a piece to size, bend a lip over on the top and hang it on the evaporator plate.

Mark

[SV THIRD DAY]

Since its all about air exchange between the freezer and refrigerator compartments, it really doesn't matter which way you are going. As the fan pushed air through (or pulls) one hole in the thermal divided it then has to flow through the other.

It also won't matter from an frost build up point of view. That is more a factor of how much humidity is in the air, how often you open the box, and how good your hatch seals are. Not bow you move air around inside the box doesn't change the amount of warm/moist air coming into the box that then plates out on the holding plate or evaporator plate.

BUT once that frost builds to more than 1/4 inch....get it off of there because you will start losing efficiency of heat moving into the plate/evaporator and being removed from the box.

[mikereed100]

FWIW we do not even use a fan. I just cut holes in the divider between fridge and freezer until the ice cream stayed hard when the fridge was in the low 40's. I know a fan is recommended to keep temps uniform in the fridge side, but in practical usage we have not found this to be an issue.

[a64pilot]

I have two 2" holes in the bottom of my divider, no fan, simple convection seems to keep air flowing very slightly. Duct tape covers about half of one hole or the milk freezes in the fridge.
Although I can see where a thermostatically controlled fan would be slick, it complicates things as it's two more items that can break, I like KISS, but put a little twist on it, I say if its simple and works, it ain't stupid

[SV THIRD DAY]

Originally Posted by mikereed100

FWIW we do not even use a fan. I just cut holes in the divider between fridge and freezer until the ice cream stayed hard when the fridge was in the low 40's. I know a fan is recommended to keep temps uniform in the fridge side, but in practical usage we have not found this to be an issue.

That's what we have found also. In the majority of installs a simple divider with holes properly placed sets up the natural convection air movement to keep the refrigerator and freezer in the proper temp ranges. But....as with most things are on boats, there are exceptions to almost every norm. Depending on the box shapes and more importantly how the box is loaded with food and filled, some boxes just can't get a good convection air movement and on those a SMALL 10CFM air movement fan can assist. But this is where it can also goes wrong on a few fronts.

The mas es bueno guy:
Living aboard on a mooring in Morro Bay, which is a popular stopping point for cruisers way South to Mexico, I get calls to come take a look at their system just to make sure all is well in exchange for a beer or cocktail, which I'm always happy to do. I opened one box and immediately got a arctic blast of cold air right in the face from their freezer hatch. They figured if a little air movement was good, then a lot is better. So they installed a Caframo 225CFM fan to pull air from the bottom of the box and blow it to the top. Holy smokes, it was like a commercial blast freezer except that their refrigeration unit never turned off and their refrigerator was having problems with freezing the eggs, veggies....heck they could make ice cubes in their refrigerator! Don't overdue your Box fan...more is not always better both from a power usage and air movement standpoint.

Another "where it goes wrong" is in the fan wiring:
Some folks just splice the auxiliary fan into the condensing unit's cooling fan that is powered by the electronic control module. What they don't realize is that the fan power outlet from the controller has over-amp protection and will trip off the control module if the power draw exceeds 0.5A. Now some get away with it because the auxiliary fan they choose is small enough so that even with both fans running they stay below the 0.5A draw, and then the Cruise Rumor grows and spreads that this is the right way to add a fan.....Bad Idea. If your system doesn't have a built in spot to power an Auxiliary fan, then the best way to go is to install a low power draw relay on your condensing fan circuit and have it pick up what ever type of auxiliary fan you want/need. This way there isn't a risk of tripping off your refrigeration unit when you want/need it most, which of course is always when trouble happens right!

[colemj]

Originally Posted by SV THIRD DAY

Another "where it goes wrong" is in the fan wiring:
Some folks just splice the auxiliary fan into the condensing unit's cooling fan that is powered by the electronic control module. What they don't realize is that the fan power outlet from the controller has over-amp protection and will trip off the control module if the power draw exceeds 0.5A. Now some get away with it because the auxiliary fan they choose is small enough so that even with both fans running they stay below the 0.5A draw, and then the Cruise Rumor grows and spreads that this is the right way to add a fan.....Bad Idea. If your system doesn't have a built in spot to power an Auxiliary fan, then the best way to go is to install a low power draw relay on your condensing fan circuit and have it pick up what ever type of auxiliary fan you want/need. This way there isn't a risk of tripping off your refrigeration unit when you want/need it most, which of course is always when trouble happens right!

While all of this is correct, if the fan one is using to transfer cold air through a barrier comes anywhere close to tripping the control module, then one has made a very poor choice of fan.

This type of fan only needs to be a little 25-40mm computer fan. These things generally draw 0.01-0.02A, which is less than most relays draw.

Mark

[SV THIRD DAY]

Originally Posted by colemj

While all of this is correct, if the fan one is using to transfer cold air through a barrier comes anywhere close to tripping the control module, then one has made a very poor choice of fan.

This type of fan only needs to be a little 25-40mm computer fan. These things generally draw 0.01-0.02A, which is less than most relays draw.

Mark

Reference Blast Freezer....

But good clarification.
My comments about the relay really apply more for the auxiliary cooling fan/venting for the condensing unit if mounted in a tight closed space.