Fridge Fan, Part Deaux

[geo]

My thanks, compliments, and kudos to Rick for inspiring me to do this modification!

So, I don't know whether to claim to be lazy or a technophile, but having to mess with a switch to operate a fan to boost airflow across the refrigerator's condensing coils seems to be one of those things I would forget from day to day. I started looking around and found a "thermistor controlled computer case fan". This fan is a Silenx iXtrema Pro Thermistor Fan (Model XP7414T). The thermistor starts the fan at 70F (21C) at 24 cfm and as the temperature increases to 168F (75C), the airflow increases to 72 cfm. This fan is also amazingly quiet! Thanks to Rick's previous superior advice, I decided to mount this fan directly on the lower outside louvered cover of the refrigerator such that it would push air into the space below the condenser coils. I have a Dometic RM1350 refrigerator mounted in the kitchen slide, and it does have a thermostat-controlled circulation fan located about three-fourths of the way up to the upper louvered vent within the condenser coil space.

I guess everyone knows that this August (2011) has been very warm in north Texas. We have our Alpine parked under a shelter, so it is pretty much in the shade until late evening. But with temperatures in the shade at 101F to 108F (38C – 42C), the refrigerator was working hard to keep the inside temperature around 45F (7C), and if you opened the door, that quickly rose to 50F(10C)! And what good is a refrigerator if you can't open the door for a beer! I installed the thermistor fan and let it run for 24 hours before checking the temperature. With all conditions the same (will it ever cool down in Texas?), the refrigerator temperature dropped to 40F (4C)! Though I didn't time it, once the door was opened, the recovery time seemed much quicker.

So, with my own version of pretzel logic, if one fan did this good, two fans would do even "gooder"! I mounted a second Silenx fan next to the first fan. (See Fan1.jpg). Since I wanted to make this more permanent, I installed a Universal Two-Wire Connector so I could remove the louvered cover easily, and cover the hot wire when disconnected. (See Fan2.jpg) I soldered the fan connection leads to this two-wire connector so that either fan could be removed and replaced easily. (See Hookup.jpg) When I close this louvered cover, I place the thermistor leads above and to the side from the fans across some wiring within the space. Now, as the north Texas day heats up, these fans push 48 cfm to 144 cfm into the condenser coil area of the refrigerator, and the factory installed Dometic fan gets a big boost from below! Waiting 24 hours and another hot Texas day, the refrigerator was at 37F (3C)! And the fans will activate when needed, and shutdown when not needed!

The Silenx fans admittedly are more expensive than the 3" muffin fans taken from an old computer case or power supply. The first fan I got a Fry's Electronics in Irving – it was the last one on their shelf. The second fan I got from Amazon.com. Both fans were $17.95 each. I consider this money well spent since now the DW hopefully won't worry about food spoiling in the fridge, and I don't have to keep running outside to turn the fan on or off.

Ron

[mpv1948]

Geo
We purchased an Alpine 3450 at the end of April this year. Ours also has the Dometic RM1350 4 door refrigerator. For the 1st 11 days, that this frig was running, there was absolutely no sound. On May 20th, while we were camping, the refrigerator started to make a loud whining sound. Camping World has replaced these fans twice already & the sound continues. I am asking everyone with this same refrigerator if theirs is making any strange sounds like ours. Dometic keeps telling us that these fans make noise. I believe if they were suppose to make noise they would have done it from day one.
We know of 2 trailers in our area that have this frig & neither one of them makes any sound. We told Dometic but they keep saying this is not so.
Your response would be greatly appreciated.

[geo]

Mpv1948 -

The Dometic fan in our unit can be heard when it is running, but it's just normal fan noise. No strange sounds, just a fan hum. The two fans I put in are low noise. You can't hear them when you are standing next to them. Is the Dometic booster fan properly attached? This is an important fan since the air circulation uses two side vents.

Ron

[mpv1948]

Thanks for your reply. Camping World installed another set of fans again on Monday. Again they were making the same high pitch sound. They even commented this is not normal. They contacted Dometic again & sent them a sound video for the tech to check out the sound. That was the 4th set of fans with no solution to the noise. They will continue to change them until it is just a normal fan sound.

[JRTJH]

If they are on the fourth set of fans and the noise is still the same, it's not the fans, but probably the mounting/configuration that's the problem. If the fans are mounted attached to the metal framework or touching the metal cooling fins of the reefer, the vibration will transfer to the reefer and you'll hear it as a high pitched whine inside the trailer. I'd look very closely at what may be bent or misaligned causing the fan housing to rub or touch something it's not supposed to contact. It may not be a Dometic problem, but could be a Keystone issue if they misaligned a mount or structural component in the reefer compartment.... I'd ask them to look closely at the installation. Might have to completely remove the reefer to critically inspect or evaluate the structure as well as the reefer itself.

By the time you get through a couple more sets of fans, it would have been cheaper to just replace the entire reefer..... Wonder if Dometic thinks along those lines? Probably not..... <sigh>

[mel07green]

(Melinda's husband) Thank you so much for posting this. Very articulate, informative and useful as usual. I'll start modifying our fridge as soon as the fans get here. We're having a similar problem here in Chico - been in the 90s.
William

[mel07green]

Hey, what is the polarity of the fan wires at the three wire plug connection? I see only two of the plugs in that connection actually go to a wire. Which one is the neutral?

[geo]

There are two wires going to the three wire connector. Middle is hot and the outside is neutral. If you use an insulated two wire connector in the connection, be sure to connect the positive from the fridge connection block to the enclosed insulation side of the connector. (Cuts down on the sparks!)

Ron

[mel07green]

Thanks. Hey, how long does it take for them to come on? Seems hotter than 70 here at the moment.

[geo]

William -

They should starts immediately if warm. Try reversing the leads. Positive may be hooked to negative and vice versa. Let me know if the start.

Ron

[sandy43]

This is really a great mod thanks to geo. Everyone should do this as summer is approaching and the forecast is similar to last year. Thanks

[hankaye]

geo, Howdy;

where did you place the thermisters?????

hankaye

[geo]

Originally Posted by hankaye

geo, Howdy;

where did you place the thermisters?????

hankaye

Hankaye! Hope you and Rascal are doing well!

The thermisters are attached to the fans on about an 8" lead. When I put the cover with fans in place, I lay the leads across some wiring above the cover area. That way the thermisters are "airborne" and not laying on anything too hot or too cold. They control the fans at variable speeds, so initially, the fans start slow and increase as the temperature rises.

Using the switch that others have used is a good idea also. I'm just lazy and forgetful!

Ron

[hankaye]

geo, Howdy;

Thanks for that.

Rascal is doing better after the trip. He HATES being cooped-up in the truck while we travel. He is, after all, a dog of action !


hankaye

[sandy43]

geo, I ordered my Silenx fan this morning, should be here next week. Only did one for now. Question: Your picture shows the red wire to 12vdc and you show a neutral white. Does the fan only have a red and white wire? Is it easy to see in the refrig opening which is hot (12v) and which is neutral. The picture is a little fuzzy. Does it not have a ground, didn't see that wire or is it not needed. I'm no electrician and don't want to burn my trailer up.

The mounting I can take care of. The wiring spooks me a little, so all the help I can get is well appreciated. Thanks

[geo]

Hankaye - So very true, border collies are Action-Bound. I have yet to see one that really likes to ride! But as you know, they are very smart! Rascal might take the trip better if you let him drive!

Sandy - Yes, cell phone pictures do leave something to be desired. I'll check this weekend, but I believe you have seen it correctly. No, this fan has no ground. It only pulls a few milliamps. And the thin wires aren't going to burn up anything but themselves.

But if you want to test, try this. Do you have a 12VDC source? Sure you do. The fan will probably come with a polarized disconnect. So don't let the "hot" pole ground out when you mount it and disconnect it. Before you mount the fan to the cover, twist the neutral to something on the frame, or attach the white to the neutral. Hold the thermister with your fingers gently in the palm of your hand. Or ask your DW to hold it between her palms (no one will be shocked). Need to warm it up a bit and keep it warm. Now, just touch the red wire to the 12VDC source or pole. It's not going to spark. Now, does the fan start to turn? It will be slow at 98F. But it will start to turn a little at body temperature. If it turns then you have the correct wires. If it doesn't, switch the wires. I expect it will start a low rpm turn. By the way, the thermister is very small. It's the black dot at the end of the wire pair. Don't cut, pull apart, etc. that wire pair. See the instructions. Just lay that wire pair up on some of the wires above the cover where it will be out of the way and have air around the thermister.

After checking the wiring and the fan (my DW has warm hands!), I went to the auto parts store and got a pigtail disconnect. I wired the insulated female lead to the hot 12VDC. That way I can't accidently ground out that thin 28 gauge wire and fry it!

My SIL doesn't care for electricity either. He waits until I'm around and I get to do it for him!

Ron

[hankaye]

geo, Howdy;

Your a funny person....... Rascal dosen't have a license to drive
and ....... he's got no thumbs....

hankaye & Rascal (arf)

[geo]

Sandy43 -

The middle wire of the Silent is the hot, positive lead. The outside leads are neutral. I don't believe it matters which one you pick. It's been a while since I wired them up. Best results - trial and error. Unless you disconnect something else, these little fan wires won't hurt anything. If nothing else, the will act as their own fuse and melt.

Hankaye, Now I know from somewhere in the past, I've seen a border collie driving a Model A with a man riding shotgun! I'll see if I can find it on You-tube. And that border collie didn't have thumbs either. I'm pretty sure Rascal would be a better driver than a lot of folks in Houston!

Ron

[sandy43]

Geo, does it make any difference which neutral wire to use? Can I just tie the 2 neutrals together and use it that way? I'm assuming the neutrals are also the ground, correct?

[geo]

Originally Posted by sandy43

Geo, does it make any difference which neutral wire to use? Can I just tie the 2 neutrals together and use it that way? I'm assuming the neutrals are also the ground, correct?

Sandy43 -

Yes, on the computer case fans, there is not really a "ground". Hmm, come to think of it, I've never seen a ground on DC. And I'm thinking hard for this time of day! Anyway, I think one lead is just dead, no connect. I believe the fan comes with a two wire connector. I spiced my two fans into an insulated pigtail connector to isolate the hot lead. I left the stock connector so I could replace the fan later easily.

Ron