Dometic Fridge Rear Panel Fans

[TX-Trek]

We're getting ready to hit the road and I've turned on the fridge (Dometic 2554) so we can load cold stuff in the morning. It's generally worked fine to date and seems to be cooling down ok. Van is connected to a 20a outlet that's used to keep batteries charged and for trip prep like this.
When we first got the van in 2019 I went through all wiring and connections to ensure everything was in good shape. I know I looked at all this but I guess for some reason I assumed this was all factory stuff.
So I'm poking around to ensure all is well and I'm looking at these 3 fans. The fridge is cooling but at the time I took the pic none of the fans was running. I assume they're on a thermostat? Van is garaged and there's definitely heat coming off the coils under the fans.



You can see a red handle toggle switch to the left of the fans - it takes power from a terminal block at the bottom of the fridge. Flipping the switch turns on the light in the switch handle but that's it. I don't see or hear anything happening. There's not a visible direct connection from switch to fans - the wiring goes into the back panel. I didn't check for continuity while everything is plugged in. Tomorrow I'll check voltage at the switch.

The fans don't look like someone added them but I have no idea about the switch and I'm fuzzy about the fan operation parameters. If anyone can share some knowledge I would appreciate it. Thank you.

Edit .....The van has a combo microwave/convection oven in the same cabinet above the fridge. I'm wondering if these fans are related to ventilation for that appliance but it still doesn't explain that switch. I'll do some more looking tomorrow, maybe shut the fridge off to try to run the microwave and see if the fans come on.

[mkguitar]

someone has added a kit. there could be a temp activated switch.

in which case if could be kinda cycling that is alot of fan...maybe too much.

my own efforts- my van came with a single fan mounted under the fins with a thermostatic switch.

but the airflow was a mess- disordered. air being pushed up was not directed through the fins and was not being exhausted out the vent

I added a piece of sheet metal to ensure that any air moving up through the plenum was directed through the cooling fins. ( probably the best move)

I then put 3 fans similar to yours and over time realized that in most cases 1 fan is fine...I have a 2nd on it's own switch which I use if I find heat is not being shed quickly.

I also have a small fan inside the fridge ( the 3rd switch)


i have a devil of a time with pics on this forum- it's upside down....sorry. but you can see the piece of sheet I added


I live in PHX and in the heat of summer it can be a struggle to get the temps down before a trip. I usually run the roof ac overnight and have jugs of water in the fridge ( "thermal mass" ), I may also put in blue freezer packs from the house fridge

[TX-Trek]

Mike, I greatly appreciate the info. My comment about the microwave was dumb, I remember removing it to replace the rotisserie motor, it was just a 110v plug. So no fan relation to the microwave. Fridge is cooled down but like many, we've seen temp fluctuations during a trip, but it's not failed. Yet.

While we're doing last stuff today I'm going to leave that toggle switch on to see what happens, and I'll look more closely at the wiring and to see if I can find a thermostat related to these fans. I'm assuming initially that in order for the fans to work that switch needs to be on. I also will check the switch itself to verify its actually controlling current.

I do keep a small fan running inside the fridge.

[TX-Trek]

An aha moment lol. I went out and flipped that switch on and the fans came on. I can definitely feel warm airflow from the coil assembly. The fans didn't come on last night so I'm figuring a thermostat somewhere per the kits that you mentioned.

I'm leaving the switch on to confirm fan cycling. I'll admit that switch has never been on, most of our trips are in cooler weather, but I noticed our last trip in April had warmer temps and although the fridge worked, we encountered some temp fluctuations along the way.

So it seems that on this trip going from TX into NM, AZ and then up to northern states I should leave the switch on and let the fans cycle as needed?

[avanti]

If I had such a setup, I would replace the bang-bang thermostat with one of these:

fan controller.jpg

Fans will run often, but mostly at a very low speed -- often too low to hear. Pretty optimal.

The particular listing above is ancient. But, there are many variants available. They are used in computer and HiFi cabinets.

[Doneworking]

Our Roadtrek 210P is three years older than yours but essentially little difference since they mostly just tweeked them from year to year.

I added a single fan with a toggle switch about ten years ago but seldom use it. We have not experienced the many cooling problems often discussed on this forum......yet.

We are fortunate to keep our RT in an enclosed garage at our home which has HVAC. We turn on the refrig to AC power, let it cool down several hours and then load it up with cold stuff out of the refrigerator in our home. That mass of cold food really helps the RT refrigerator out in keeping cool at the beginning of a trip. Going down the road, if it is really hot weather we run it on propane and if not very high temps are encountered we run it on DC while driving.

[mkguitar]

Originally Posted by TX-Trek

I should leave the switch on and let the fans cycle as needed?

I usually switch mine off when driving, I have good airflow...

how do I judge that ?
If I put my hand near the vent and it is very hot- more radiating heat than moving hot air out...I turn on a fan.


If the fans are on and the air is mildly warm, I turn off one of the fans.

the sheet steel made the biggest difference I think


I can get my fridge 60º below ambient- my challenge is when it's 110º


My fans draw about .385 amps each.

Some speed controls don't reduce energy use, they drain ( waste) power to ground to control the fan speed.
We do alot of boon docking managing energy use is important, that 1/3rd of an amp adds up over a couple of days ( 8 amp-hours daily, each fan)

instead of controlling fan speed, I choose how many fans to operate.

your thermal fan switch is probably attached to the tubing near your cooling fins and will be a little metal canister about 9/16" across and 1/2" high with 2 wire terminals,

Mike

[avanti]

Originally Posted by mkguitar

Some speed controls don't reduce energy use, they drain ( waste) power to ground to control the fan speed.
We do alot of boon docking managing energy use is important, that 1/3rd of an amp adds up over a couple of days ( 8 amp-hours daily, each fan)

instead of controlling fan speed, I choose how many fans to operate.

Modern motor speed controllers (such as the one I referenced) use PWM--they basically turn the controlled device on and off thousands of times a second--so they are extremely efficient. It is how LEDs are dimmed, and works just a well for most motors. They go smoothly between "full off" and "full on". So, no power is wasted. I really believe that this is the optimal solution to the problem at hand. Install it and forget it. At least that has been my experience.

[booster]

Originally Posted by avanti

Modern motor speed controllers (such as the one I referenced) use PWM--they basically turn the controlled device on and off thousands of times a second--so they are extremely efficient. It is how LEDs are dimmed, and works just a well for most motors. They go smoothly between "full off" and "full on". So, no power is wasted. I really believe that this is the optimal solution to the problem at hand. Install it and forget it. At least that has been my experience.

What kind of energy use are you seeing for the controller itself? The one I got a few years ago was a PWM but it used about as much energy as running the fan slower saved. Only benefit was the fan was quieter.

[TX-Trek]

This is a great education for me and I thank you all.
From my post this morning the fans have run continually and the fridge and freezer temps have come down about 4d. Since the fridge had all night to run without the fans I'm thinking that their running has been of benefit.
I'm looking for a thermostat attached to something on the back and I'll look again based on the description given. I'm assuming line in to coils will be hotter - I checked one with laser gun at 130d, line at other end is 95d. Coil midpoint last night with no fans was 125-130d, today with fans on its 95-98d.

Due to leaving tomorrow am I can't do much more than continue to learn from your info - it's of great help to me. But in the meantime I'll be able to get a better game plan together - for sure I'll unbolt the fan panel to get a look behind it. I'll try to locate the thermostat.

[avanti]

Originally Posted by booster

What kind of energy use are you seeing for the controller itself? The one I got a few years ago was a PWM but it used about as much energy as running the fan slower saved. Only benefit was the fan was quieter.

Well, I never actually measured the overhead of the speed controller, but I have measured the ESP32 boards that I am using for my van automation stuff:



That processor was actively executing, and is more than adequate for implementing a PWM motor controller. 0.06 amp isn't much -- typical 12V computer fans might be .25A at full speed, so...

[TX-Trek]

I looked very carefully at and around the coils/lines and can say with certainty there's no attached thermostat, actually nothing is attached.

I'm wondering if the fans are controlled out of the contro board, see this pic.


The screwdriver points to the terminal block connecting the switch to 12v supply. You can see the feed side wiring going through a green inline fuse and then to a relay mounted on the back panel. I see wiring going from the relay into the board and I believe this to be control to the relay coil.

The board itself is Dinosaur Electronics labeled 3850712.01 Replacement. Based on experience replacing original Suburban furnace board with Dinosaur, I'm wondering if this is also a replacement board, not original. If so then along with the fans , it looks like someone's been in here before. Not an issue but I'll look up that board to see if there's something controlling aux fans. Is this a reasonable approach?

[mkguitar]

I wouldn't tear it all apart unless there is a problem.


BTW my thermostatic switch is up top - it was attached to the first cooling fin.


When I was wiring up my fans, I found a 30A fuse for the DC to the fridge behind my control box...glad I found it just in case I ever have a problem

[TX-Trek]

Yes I think that board has 1 or 2 fuses behind the cover. The fans are still running which I don't see as a problem. We're loading the fridge now and all seems to be ok. When we're back I'll pull that fan panel off only to look behind it. Easy and no need to disconnect anything. I still want to fully understand the control side of these fans.

We have a similar setup as Doneworking, van is in enclosed garage with window ac. As I mentioned its currently connected to 110v, when we drive the fridge is on DC power without issue. We don't boondock so while parked we're on ac power. I've never run the fridge on propane but can give it a try if we hit high temps.

[ChicagoTom]

I replaced my Dometic with a like for like. When I went to install it, I was surprised to see a factory installed fan. I can tell you from experience that it's pretty useless. I'm getting the same results as the previous one. I am one of the few who really likes the absorption. I stick a decent airflow rechargeable fan on the top shelf pointed at the evaporator. I have a second one charging and switch them 2-3 times a day. Ex Refrigeration Tech for what it's worth. BTW I disconnected the 12 volt option for the 3-way. It's pretty useless and too many horror stories of people forgetting to switch it back and killing their house battery.

[TX-Trek]

Thanks CT, we're about a week into our trip, currently in Alamogordo NM, mid to high 80s and lots of sun heat load. No shade where we are. I run the 3 fans all day and they seem to help fridge temp to stay generally stable, within about 5 degrees. When driving or at night in 60s temps I turn them off.

I also keep an interior fan running all the time in the fridge. The freezer compartment is getting some frost. Freezer was well below freezing but fridge temp had gone to about 50, I think ideal is 40ish? I cleaned the freezer so hopefully the fridge temp will come down a but.

So far the fridge is doing what it needs to do - when parked at a site we always run it on ac, driving we switch it to dc. Short stops we just leave it on dc, not a problem with batteries.
I honestly don't know what I may replace it with when it fails. I'll definitely use advice here on a replacement. Lots of regular fridge replacements, but I like the ability to run while driving or when parked for short intervals.

[mkguitar]

I ran wiring for an internal fan up the condensate tube.


The fan was salvaged for an old VCR about 1.5 x 1.5" zip tied in place the gently circulate the air in the fridge