DIY RV Refer Fan Installation
I’d known for years there is a commercial refer fan made for RV’ers but I didn’t care for it’s price or looks. Seemed too small for one thing, it uses big horky D batteries for another. And only runs on 3 Volts where the refer uses 12 Volt so it’s difficult to just wire it into the refer power and eliminate the batteries. I spent years knowing I could come up with something better, but never getting around to it. After all, since I tended to stay in the west where it’s mostly dry, defrosting every three to six months wasn’t all that bad. Until recently. I was down in Florida…Orlando area, and the humidity was like 60% all the time. So my refer fins were icing up very quickly. That lowers the efficiency what with having to keep that ice frozen so my beer was warmer than I liked in the evenings. OK, time to do something about it.
So here’s what I came up with…
Like many people, over the computer years I’ve accumulated many spare computer parts. In my large pile of parts are several muffin fans. These are 12 Volt devices in various sizes and styles used to cool various systems and parts inside of computers. I happened to have a number of them and after sorting, I chose a couple that looked like they would work fine inside my refer to stir the air around, promoting rapid and even cooling. I also carry electrical connectors as well as tools to work on electrical stuff so I was all set to modify some fans and stick them in the refer.
After disconnecting the battery supply from the refer, first I checked that what I suspected was true, the fans were low enough current that they wouldn’t cause heating while running. I measured 250 mA, which is typical for these types of fans. Of course, I wanted them to run whenever the refer door was closed and stop when opened so that made the door switch the primary candidate for switching the fans off/on. Then I checked to be sure the refer light is an incandescent (has a glowing filament when it’s on). This is important for this design because a filament type automotive light bulb, as opposed to an LED light, draws much more current than LEDs and this design required that ability.
I always carry 1″ wide, 1/16″ thick double sided sticky tape with me when traveling, and I put strips of that on the tops of the fans. I cut off the plastic connectors that came with the fans, striped and twisted together the two blacks, the two reds, and some polarity marked scrap wire I had with wire nuts. Paying attention to polarity. Then routed the wire around and down to the lamp assembly, making a nice dressed installation using the channel cover used by the thermistor that wouldn’t get in the way or get hooked when moving food in and out nearby.
The lamp and door switch assembly was removed, some resistance and voltage measurements made, a grove cut into the soft plastic here and there to make entrance channels for the additional two wires, and on the backside the fan wires were connected with the negative lead to the positive end of the automotive type bulb and the positive wire to the 12V terminal of the switch. (Ignore that bulbs price in that link, you can find them at dollar stores for $1). I am still seeing this type of bulb in newer RV refers these days, though refer manufacturers or owners will probably switch to LED before long.
With that done, and the wiring dressed up, pulled the protector tape off the double sticky tape on the fans and pressed them onto the ceiling of the refer (which had been defrosted so was warm), using a cardboard shim to create a 1/8″ space between the frame of the fans and the cooling fins. (A trick to removing the fans if you need to rewire them is to let it get cool in the refer, they’ll pop off easily enough).
And here’s the picture of the results:
The fans blades are exposed so I do have to keep that in mind when I put my groceries on that shelf but it’s easy to do that. After using them for a while, I don’t really think it would make much difference which direction the fans blow.
That’s my bread and butter shelf generally. I can fit a loaf of bread and a container of soft butter under the fans, no problem. And even more. The fan on the right has some colored LEDs that come on when it’s running. Neat. But the door is shut so…
This picture shows the channel (wire race) the wires run in along the wall of the refer. It’s the wire race used for the thermistor temp control and there was room for the fan wires also. The door switch is on the right of the assembly (I’m pushing it with my thumb) and the light bulb is behind that semi opaque plastic cover. The bulb, behind that smoked plastic cover, has a soft yellow glow that is hard to make out in this picture.
What happens when the door is closed is that the switch opens and the light goes out. This means there is 12 Volt across the open switch. So the fans are wired directly across the switch and when the door is closed, they have 12 V applied so they spin. Their ground connection is supplied through the bulb. Here’s where it gets tricky. The bulb must have a very low resistance for this to work, which means if you have an OEM refer that CAME with a LED bulb in the refer, this DIY scheme might take more thought. Like, can I change the bulb to an incandescent? And, is the switch capable of handling more current? So if you want to try this DIY project, measure your voltages and check the size of the wires in there first. While LEDs only require milli amps, bulbs require amps so the wiring will naturally be larger/heavier. BTW, the manufacturer could have wired the bulb to 12V and the switch to ground, just backwards of what mine is, that will still work, you just need to measure voltages to know for sure where to connect your +/- wires from the fans.
If you do attempt to install these fans in a refer with a LED bulb installed from the factory, first, consider just using one fan. And just measure the voltage across the fan(s) during testing. If it drops more than 10% (down to 10.9 V with a 12 V supply), then the wiring gauge is too small. Or the switch has too much resistance and may be too delicate to last very long. Neither of these scenarios are all that likely but, I need to mention them in any case.
When the door is opened, the switch closes, all the current goes to the bulb and the voltage going to the fans drops to zero…so the fans stop running.
To test this setup, turn power back on using the eyebrow switch, then with the door open so you can watch, just press the door switch. The fans should spin, and the bulb will have a soft glow as the current passing through the fans causes the bulbs element to heat up a small amount. Not enough to cause the refer to heat up though. If they don’t run, or if only one runs, then you probably have the wires to the fan(s) reversed. These fans are polarity sensitive so if they’re reverse wired, they won’t spin backwards, they just won’t spin at all…but typically they won’t be harmed either. (Hint: yes, you can use a fan that has 3 or even 4 wires going to it. Just Google for a wiring diagram and wire up just the +12 V and ground wires).
After installing, I used this setup in Florida for several months. And although the evaporator fins inside the refer portion did accumulate some frost over the next 3 months I was very happy with the operation. Much less condensation accumulated and at a much slower rate. Without the fans, I’d been seeing a block of ice just 3 weeks after a defrosting.
Along with the benefit of not having to do a defrost as often, there were several other immediate benefits. My crisper items got colder faster after carrying them home from the store, stayed colder in the crisper and on shelves too, even as the ambient rose month to month, so I wasn’t throwing away spoiled fruits and veggies or moldy cheese as often. I could buy cold drinks, place them in the refer, and they’d not warm up as they did when there was quickly accumulating frost on the fins. I did have to do a defrost just before I left Florida but that was mostly because of the freezer portion having accumulated so much excess ice in that high humidity part of the country. The refer cooling fin assembly was not the nearly solid block of ice it would have been had I not installed these fans. There was another benefit, and that was the evidence I could see of seal leaks. There’d be a small accumulation of condensed water droplets here and there on the refer frame where the door seal wasn’t sealing well. So I went to work cleaning up the seal and seating it properly. Got it down to just one tiny leak that I decided to live with. No need to replace the seal.
Cost was zero since I had the fans in my computer junk box, the tape, wire nuts, and scrap wire in my supplies. If you check at a Thrift store you can probably find a couple fans for just a couple bucks. Or you might have a couple in a retired computer in the basement.
What I know about these fans is that they can last for many years running continuously in a hot computer so I’m not really concerned about lifespan in a refer. They do the job of keeping air flowing around inside the refer and simply keep it cooler in there. Moisture takes longer to accumulate on the cooling fins so there’s less need for defrosting. I’m happy with the results and wish I’d have done it sooner. Could have avoided many ‘defrostings’ over the years.
I have since moved on to a newer RV with a newer refer…this one happens to be a ’02 Norcold. It’s not on any recall list and does a great job keeping things cool so far, but I went ahead and added a single fan internally to the right side of the evaporator over a month ago. The bulb is an automotive type incandescent so I was able to wire up the fan the same as I did in the Dometic. And so far, in humidity ranging from 35% to 60% there’s been no accumulation of frost on the fins. The single fan seems to do the job as well as two fans did in my older Dometic (but I didn’t test with just one fan in the Dometic).