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Old 08-12-2019, 07:01 PM   #1
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Dometic fridge fan for outside compartment

I'll try to keep this simple, but will probably provide TMI. I have a Dometic model RM 2652 or RM 2852. Not sure which. Freezer has always been great, temp-wise. Fridge.......so-so. When I bought the RV 8 years ago, there was an inoperative fan in the back side of the fridge by the outside vented compartment. It doesn't show up in Dometic's schematics, so it was either installed by Fleetwood, or by a previous owner. I replaced that motor a year ago, but it has quit again. I also installed one of those hanging dual fan deals inside the fridge, and that has improved things in the upper two shelves, where temps stay around 40 degrees. Lower areas are closer to 50-55, so I try to keep perishables up high. One of the two fans in the inside fridge unit quit on my last trip, so I am replacing that with an identical sized computer fan that I found in my closet.

Here is my question. I dug up another old computer fan that I can install in the outside compartment. It shows a draw of 18 A on the label. Is that too much for a fan that for the most part will never shut off during the summer months here in the desert, or even in my midwest trip in July? The one that quit was a Mabuchi RF-500-12560 motor, rated at 1.5 to 12 VDC, basically a hobby motor for toy cars, as far as I can figure out.

I have checked the fridge gasket, and it is tight. Realistically, I'm assuming that this fridge is dying a slow death, as the RV is a 2005, although it is doing better now than it was 8 years ago, with the addition of the inside fans. A residential fridge is not an option for me, as all of my camping is at racetracks, most of which do not have hookups.

Thanks for any suggestions.
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Old 08-12-2019, 07:06 PM   #2
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You sure that isn't 1.8 Amps or even .18 Amps? I've never see a PC fan that pulled 18 Amps.
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Old 08-12-2019, 07:24 PM   #3
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I suspect the fan is really 1.8 amps , not 18 amps. Propane fridges should last for many years if not abused, as there are no mechanical parts to wear out. That being said, corrosion and mistreatment can cause an early death.

Ventilation fans on the other do die, and need to be replaced - especially if you are going in areas over 80.


Some people install fans with thermostatically controlled by snap switches. I am upgrading ours with a controller.

https://smile.amazon.com/Inkbird-All...39&s=hi&sr=1-3


It might be overkill, but it lets me see what is going on.
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Old 08-12-2019, 07:25 PM   #4
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18A Draw........boondocking....dead battery very quickly


RM2652 is a 6 cu/ft fridge
RM2852 is an 8 cu/ft fridge


Fridge NOT in a slide out should NOT require an external fan PROVIDED RV MFG correctly installed fridge (clearnaces, baffles if needed, no dead air space etc)
Fridges installed in a slide out require an external fan AND properly installed>


Dometic Innovator Ventilation Kit available for installation in slideouts
0.5A fan thermostat controlled'
12V DC from DC Supply to thermostat on condenser fin to fan (inline 1A fuse on DC to thermostat)

https://www.ebay.com/itm/Dometic-310...-/122192958479

**Better fans are available BUT keep amp draw DOWN)


temps abiove 42*F in food compartment show inadequate cooling process
Bad ventilation across back of fridge (drfat/airflow, fallen down installation, bad install etc)
Bad thermistor
Bad circuit board
BAD cooling unit


Unplug thermistor leads on circuit board and run fridge overnight...food compartment SHOUDL get down to roughly 32-33*F cause thermostat will run fridge continuously


IF food comaprtment cools down..replace thermsitor
If it doesn't.....
then need to 'force' cool to see if cooling unit is capable if cooling down
Unplug electric heater leads...plug directly into a known working 120VAC outlet
Run fridge 12Hrs minimum ...element energized the whole time will cause food compartment temps to cool way down.
If it doesn't ....cooling unit is obstructed/blockage
If it DOES...replace the circuit board
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Old 08-12-2019, 07:38 PM   #5
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Thanks, everyone! Shows you all how much I know about electrical matters. I put on my reading glasses, and sure enough, the computer fan does say 0.18 A.

Old Biscuit, if you are saying that I don't need an external fan for a properly installed Dometic fridge, I will save myself some additional work. It never ran for the first 5 years that I had the RV.....a mechanic who was doing some other work on the rig hooked it up for me when I asked him whether it should be running or not. All of your other information is great! I will follow your advice and see where it leads. Thank-you for sharing your knowledge!
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Old 08-12-2019, 07:45 PM   #6
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Quote:
Originally Posted by terryl View Post
Thanks, everyone! Shows you all how much I know about electrical matters. I put on my reading glasses, and sure enough, the computer fan does say 0.18 A.

Old Biscuit, if you are saying that I don't need an external fan for a properly installed Dometic fridge, I will save myself some additional work. It never ran for the first 5 years that I had the RV.....a mechanic who was doing some other work on the rig hooked it up for me when I asked him whether it should be running or not. All of your other information is great! I will follow your advice and see where it leads. Thank-you for sharing your knowledge!

IF not installed in a slideout.....external fan NOT required PROVIDED RV MFG did a proper install
Less then 1" between exterior wall and backside of fridge, no dead air space at top, roof vent over the center of fridge and not obstructed etc


External fan will not hurt...enhanced airflow is a good thing


See pg 21,22,23
http://www.fourwheelcampers.com/NewD...atorManual.pdf
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Old 08-17-2019, 03:02 PM   #7
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Update

First, to answer a previous question, the fridge is not in a slide.

I replaced the fan inside the fridge that had stopped working, so now both of the pair are running again. I also hooked up the .18 amp fan in the outside compartment behind the fridge. It is blowing the heated air down, rather than up. I read somewhere that directing the air up just puts more hot air behind the fridge, whereas having it directed in a downward direction will vent it out the grille. Don't know if this is true or not.

All of the tests were done with an empty fridge. Inside temp in the RV taken every morning ranged from 92.6 to 95 degrees. Temp inside the garage was 93 to 97.

Before both of these fans were operational, freezer temp was -3.6. Top area of fridge by the aluminum baffles was 38.9. Middle shelf area was 51.8, bottom shelf above pull out bins was 47.3. With the fans back working, the numbers changed to 32.9, 52.1 and 51.5

I moved the thermistor around for a couple of 24 hour periods, and then disconnected it for 24 hours. That had no impact on anything. I also put the end of it in a glass of ice water, and got a reading of 9500 ohms. Through all of these tests, over a period of days, top readings ranged from 32.9 to 37.4, middle 47.3 to 54.5, and bottom 47.3 to 56.3.

I did not unplug the electric heater and test it, as that step looked a little too complicated for an amateur.

Through all of this, it seems to me that the top area of the fridge is within acceptable ranges, and it is just not getting adequately circulated to the lower areas. I guess I could get one of those small battery operated fans for the lower shelf, and see if that does anything. Is it possible that the high ambient temps inside and outside the RV are the real reason behind this? Last night I put 3 bottles of frozen water and 2 ice packs in the bottom of the fridge, and that lowered the temps in the mid to lower part by 2.1 to 3.6 degrees compared to the previous day, but still above readings for safely storing food.

All opinions welcome.
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Old 08-18-2019, 11:48 AM   #8
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Problem solved

Yesterday evening, I relocated the two-fan system in the fridge from its intended location, fastened to the aluminum fins at the top of the fridge. I let it hang down with the limited amount of wiring that it had, to about 6 inches above the bottom inside of the fridge. I ran a ground jumper back up to the fins so it would operate.

That, combined with the frozen water bottles, brought the temps in the mid to lower section down to 41.3 and 41.6 degrees, which is a marked improvement over yesterday, when I took the readings this morning. Moving the fan from the top shelf to near the bottom, surprisingly also lowered the top shelf temp from 37 to 26 degrees.

Just have to figure out where and how to permanently mount this fan combo now.
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Old 08-23-2019, 10:19 PM   #9
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That external fan MUST blow UP


Backside of fridge airflow is just like a fireplace chimney
Airflow comes in via Lower Access/Vent Louvered Cover......natural draft affect pulls the air UP across backsie of fridge (up thru the absorber tubes---those large slaneted ones) then acroos Condenser FINS (at top of fridge) and then exists out roof vent


Swaps the wires on that external fan and have it blowing upward....it will help PULL air in thru lower vent and exhaust it UP and out Roof Vent


Unplugging thermistor SHOULD have caused food compartment temps be in in the mid 30's IF ---BIG IF---the cooling unit is actually capable of functioning porperly


Heat (electric or propane) boils the ammonia solution into a vapor.
As it flows across condenser section the FINS remove the heat from the hot ammoia vapor condensing the vapor into a cool liquid ammonia.....which then comes in contact with the hydrogen gas --that causes the ammonia to super cool which then goes thru the Freezer Evap Coil where it absorbs the heat from freezer section then onto the food compartment Evap Coil to absorb heat in food compartment section.


Freezer has to be cooled down to 10*F or lower in order for the super cool ammonia to have ability to absorb heat in Food Section


Obstructions/Blockages in section of tubing between freezer and food compartment do occur...freezer functions normally but food compartment struggles to get down in temp


To TEST if cooling unit is cabalbe and doesn;t have blockages you can:
*Unplug the electric heater element leads from circuit board
*Plug the leads directly into the 120V AC Outlet (just unplug fridge power cord and plug leads in)
Element will be energized continuusly....bypassing circuit board and ALL controls
Run fridge minimum 12hrs with element direct and then check food comaprtment temps.

IF nice and COLD.......bad thermistor or circuit board
If NOT cold.......cooling unit is blocked. And is done for.
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Old 08-24-2019, 08:20 AM   #10
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One more thing to add is to check the door deals, you can do this using the dollar bill test, close the seal on the bill and see if there is resistance when you pull it out.
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Old 08-24-2019, 03:24 PM   #11
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Thanks for the input.

I took your advice on the outside compartment fan, Old Biscuit, and ended up having to remount it upside down, as apparently it (being a computer fan) is polarity protected, so it wouldn't operate by reversing the wires.

Also, last week, I relocated the dual interior fans from a hanging position on the upper fins, to laying flat on the narrow top shelf, blowing cool air straight down towards the lower shelving areas. I am satisfied with the results, as this step, combined with 3 single serve frozen water bottles, had the top shelf at 26.3 and the middle and lower areas at 41.3 and 41.6. The freezer was -11.5. The bottles still had ice in them almost 24 hours later.

As far as testing the cooling unit, I'm still not clear on the next step after unplugging the electric heater element from the circuit board. When I attempted to do that last week, the end connectors that came off the board didn't look like anything that could be plugged into a standard 120V AC outlet, and I didn't want to start messing around with jumpers and end up frying something.

I was also able to get a good look all the way up the back of the fridge to the roof vent today, and there are no obstructions or fallen down insulation. The top cooling fins just south of the vent appear dirty, but there would be no way of getting access to them from inside that compartment.

I also cleaned the fridge gasket and did the dollar bill test. Not sure how much drag there is supposed to be on the bill, but there was some. I did notice that I can push the fridge door in about another 1/8 inch, but the latching/release mechanism is not adjustable, so not much to do in that area.

Since I've met my overall goal of lowering the temps in the middle and lower part of the fridge from the low to mid 50s to a now 41 degrees, I think I will leave well enough alone for now. Reversing the direction of that outside fan may help even more.

Thanks again!
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