Sunday, June 26, 2011

Cooling the Refrigerator With Muffins Fans

Removing heat from the coils on the back of the fridge will improve cooling inside the refer. Air enters the vents through the outer door and exits via the chimney due to convection. When it's hot out, and especially when the sun is heating the side where the fridge is, cooling efficiency suffers. Adding one or more fans is intended to help improve things.

Two ways to cool the coils: 1)  Install a 12 volt muffin fan down low to suck in air. 2) Install a 12 volt muffin fan above the coils to force air out of the vent. If the fan were installed on the chimney with no internal ducting, it would tend to pull air in from the open edges of the chimney cap. So an internal pipe (duct), should be as large as the fan diameter and should extend down to the top of the coils.

When offered a choice I often take both.

I installed two muffin fans in the refer vent. One low to pull air in and send it up. The second on top of the coils to to pull hot air off the coils and send it up through a tube. I found a tin tube at Lowe’s just the right size for the fan. [I think the duct is used to vent hot water heaters – three bucks] I only needed to cut the length of the duct to match the distance from the top of the coils to the top of the vent and also cut notches in the tube to be able to slide the fan into the tube.

refer fan

This shows the lower fan which is bolted, on one corner, to existing duct work. At the far left, you can a red off/on switch. Power is taken from the terminal block just below the switch – pink and white wires. Wires also led up to the other fan at the top of the coils.

[The Reset Button is an almost unknown item that trips when the refrigerator is stressed. I marked it when I found out about it. It has nothing to do with the muffin fans. Thanks to Mike Sylvester]

I took pictures of both fans, but can not locate the upper one and it’s a lot of trouble to take it all apart for a picture. Sorry.

Note: A $25 1.8 watt solar panel from Amazon or Harbor Freight would be more than enough to power the fans. In fact, it could power over a dozen fans. The fans only use .1 watt combined and we can spare 2.4 amps per day to spend on cooling, so I just wired into the 12-volt power in the outside compartment.

So, Does it Work?

With the temperature control set on 4 in the hot, humid south, I got these readings with the refer running on ac.

                 Outside         Refer    Freezer

Fan off          88                49          10

Fan on           95                47            7

So with a 7 degree increase in air temperature, the refer cooled off 2 degrees and the freezer 3 degrees. I call that success. Coupled with the muffin fan inside of the refer, I was able to get close to ideal temperatures.

All readings were made with an IR gun in the same place each time. The sun was on the outside refer door at all times. Footnote: A thermometer in the refer recorded temps four degrees cooler than the IR gun indicated, which I think is more accurate. While 43 is 3 degrees more than ideal, we could increase the control to level 5 and probably get to 40.


- Ideal temperatures: Refrigerator 36-40 and Freezer 0 – 8.

- I observed substantial differences in temperature in different areas of the boxes. In general, the right side is cooler than the left and the back is the coolest.

A fan inside the refrigerator

Consider installing a small muffin fan inside the refrigerator to move the air around. I followed another’s lead, wiring mine across the door switch for the interior light. The fan is attached with nylon ties (around the wire shelf, through the mounting holes in the fan) Pick a location where the fan will be out of the way of food storage. Quick and easy and never a need to replace batteries.

refer fan 3

All ideas for these fans were taken from that cool guy bumper. Here is how he mounted his.

refer fan (2)

How To Do It

Tools: wire stripper/crimper, needle nose pliers.


A muffin fan. Computer repair stores would be a good local source.

Plastic ties to secure the fan to a shelf

The terminals described below which are available at any hardware, automotive store, including Wal*Mart.

Wire connectors come in several sizes to accommodate wire sizes. The common sizes are colored coded to indicate the gauge of wire they are intended for.


16 – 22 Red

14 – 16 Blue

10 – 12 Yellow

clip_image002 Female terminals      clip_image004   Male or spade terminals

The refrigerator wire and fan wires call for size red.


Remove the plastic light cover by squeezing the top and bottom edges. You will find red and black wires exiting the sidewall of the refer. [I am told that some units have two black wires. If you have that configuration, you may need to experiment with a VOM to see how they are used]

refer1 small    refer2 small

Left most arrow on the photo above right – The black wire coming out of the hole in the sidewall was, and is, attached to the spade terminal to the left of the lamp. I cut off the Dometic terminal and used a red colored female disconnect terminal inserting both the original wire and adding the black wire from the fan to it. [Note muffin fans are normally polarity sensitive and will run only if connected correctly. If your fan wire colors are different, experiment to determine what’s what]

The middle arrow – This shows the red wire from the fan connected to a male disconnect that is merely wedged into the plastic cover where the red Dometic wire terminates. That's all you need to make good contact with low voltage DC.

Right arrow – the plastic cover that contains the Dometic female disconnect. There was a flap on the plastic cover that I cut off to be able to insert the spade connector. To remove the Dometic connector, grasp it with needle nose pliers and gently pull toward the back of the refer.

Connected in this manner, the fan is always on, door open or closed. The fan is off when the refrigerator is off.

I observed a 5 degree drop in temperature using this fan.

The fan will use about 2.5 amps a day, about 1% of battery capacity.

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