Re-thinking the RM8551 4.3

[santacruzer]

Originally Posted by bdornbush

I have one of the newer fridges (April, 2015) with the single fan at the bottom. I can see it through the lower access panel. The wires from the fan seem to go up behind the fridge. I would like to put the fan on a separate switch as others have done, but I don't see the thermal switch to bridge across. Do I have to remove the fridge to get to it?

I have been tracking my fridge temps for the last week or so, and will publish soon. We had a day at 100 degrees early this week, and that spiked the fridge to 48 degrees, so I feel I need to do something, but the less I do, the better for me.

I'm looking at that as well. I don't believe you need to remove the frig, just the front fascia panel and the insulation on top of the fridge. I had the front off last week, but didn't have time to pull the insulation. I BELIEVE the fan wire runs along the top and connects up to the circuit board. It will be Sunday before I have a chance to look at it again, but I will post a photo of what the front of my fridge looks like, it's much different than the one just posted. My trailer is from November '14.

[Jubal]

On our two fan with the junction block/buss on top of the fridge version of the 4.3 fridge the ground and battery postitive for the cooling fan are connected directly to the junction block and not to the control panel. The black ground wire from the junction block is routed directly to the fans. The red positive wire runs from the junction block to the thermal switch on the condenser which completes the circuit to the fan if it ever closes. If your junction block is low and you can access the fan, you can splice in a wire to the red wire going to the fan, supplying battery positive through a switch wired to the battery positive supply at the junction block. This would eliminate the thermal switch control of the fan though which does not work adequately. If you cut the red wire from the thermal switch to the fan be sure to insulate it. You cannot access the thermal swich on the condenser for the bypass switch mod without removing the fridge.

[santacruzer]

Originally Posted by Jubal

On our two fan with the junction block/buss on top of the fridge version of the 4.3 fridge the ground and battery postitive for the cooling fan are connected directly to the junction block and not to the control panel. The black ground wire from the junction block is routed directly to the fans. The red positive wire runs from the junction block to the thermal switch on the condenser which completes the circuit to the fan if it ever closes. If your junction block is low and you can access the fan, you can splice in a wire to the red wire going to the fan, supplying battery positive through a switch wired to the battery positive supply at the junction block. This would eliminate the thermal switch control of the fan though which does not work adequately. If you cut the red wire from the thermal switch to the fan be sure to insulate it. You cannot access the thermal swich on the condenser for the bypass switch mod without removing the fridge.

The red and black wires from the fan run up the back and it looks like over the top, but there's no direct connection to the buss block, which makes me believe they picked up the power somewhere at the circuit board. Your approach makes sense, but I would still need to get wires over the top to provide the switch I want on the front panel. PITA. In a previous life I wired a fan on my old pop-up, but switched it at the outside panel access, which was cumbersome to turn on when needed. Don't want to do that again.

Bob

[santacruzer]

Here's the front fascia of my Dometic 4.3. Modal lights are blue. And the switch I'm planning on using, it's a Conduct-Tite! 84840, from O'Reilly. It should fit either to the left or right of the existing lights. Lastly, is this little white square the thermistor? If not, what is it?

[cpaharley2008]

That is the thermistor....

[dave1]

Originally Posted by santacruzer

Here's the front fascia of my Dometic 4.3. Modal lights are blue. And the switch I'm planning on using, it's a Conduct-Tite! 84840, from O'Reilly. It should fit either to the left or right of the existing lights. Lastly, is this little white square the thermistor? If not, what is it?

That's the same frt panel as I have. When you remove it you should find a flat wire abt a 1/2 inch wide coming from the panel. Your fan sensor should be in the top back left corner of the fridge in the condenser fins. As I remember the fan wires ran up the back and we're not visible from the top. You could wire as described by others and get the wires up from the outside.
I'll be pulling my fridge next month and will post pictures of the single fan model for future reference.
Nice switch!
Dave

[MyronL]

I emailed the Snip-the-tip people yesterday about the failure of their thermostat in my RM8551. I may be eating some crow. Their customer rep quickly replied... that I got the wrong "Snip the tip":

"...You actually ordered our standard thermistor, which will not work on the 8551...."

Who knew?? Said send it back and they'll send me the right one for my fridge.

[dave1]

Originally Posted by MyronL

I emailed the Snip-the-tip people yesterday about the failure of their thermostat in my RM8551. I may be eating some crow. Their customer rep quickly replied... that I got the wrong "Snip the tip":

"...You actually ordered our standard thermistor, which will not work on the 8551...."

Who knew?? Said send it back and they'll send me the right one for my fridge.

That's funny! At least now we know your extension cords and garage circuits are good and the company is very responsive to their customer.
By the way I've been told pigeon is much better eating than crow!!

Dave

[Zardoz]

Originally Posted by cpaharley2008

That is the thermistor....

Not to split hairs, but that is the thermistor mounting plate. The thermistor itself is actually attached to the back of the plate; it's a little plastic cylinder that's pushed into a moulded piece on the back side. To remove the thermistor, pull up on the wire and it should come right out. Or, just remove the screw holding the mounting bracket to the wall of the fridge and you'll see how it's attached.

[santacruzer]

After pondering this a while, I think the best solution for me is to just make this a two-fan model, by installing a second one, independently switched. I have a fan and switch from a project on a previous trailer, and access to power is right in front of me. Just need to position the fan and feed the wire, which will probably be the most biggest hassle.

[Jubal]

Originally Posted by MyronL

I emailed the Snip-the-tip people yesterday about the failure of their thermostat in my RM8551. I may be eating some crow. Their customer rep quickly replied... that I got the wrong "Snip the tip":

"...You actually ordered our standard thermistor, which will not work on the 8551...."

Who knew?? Said send it back and they'll send me the right one for my fridge.

Myron, will you be installing the correct RM8XXX adjustable thermistor ? I am having a difficult time deciding whether or not to do so.

[Klem]

I have not replaced my thermistor and have no plans to do so unless troubleshooting results in that finding (resistance reading at 32f).

I have moved it around the wall and box to test the 'coupling' as explained by a frig rebuilder. Further away will result in it being less responsive ... so it will cool longer .. but also the temp will rise higher.

To me a thermistor is the equivalent of your wall thermostat at home. And the way you test it is see if the temperature in that area is tracking with the device. You wouldn't move it around on the walls unless there was sunlight hitting it, a draft, etc? And you wouldn't change it just because your furnace was not putting out enough heat?


I suggest testing your thermistor by running a simple test. The location of the thermistor is based on 'coupling', like your wall thermostat, so your temperature setting gives you the results you believe it should. It will swing high/low based on door openings etc. but that's normal. If you set it to 5 the burner will be on more as the frig tries to achieve that temp. IF it's hot outside that additional heat may be counter productive. For me, if it's warmer I'd just like to see frig temps in the low 40s and then shut that burner down.


Simply test your frig and freezer temps on bar 1, 2, 3, 4, and 5. You should see 1 in the neighborhood of 44f in the frig. 2 = low 40s, 3= close to 40, 4= high 30s, and 5 in the mid to low 30s. Then pick the temperature you would like the box to be and leave it there (like your home wall thermostat).


Don't replace the thermistor IF you have the range ( mid/low 40f down to mid/high 30f) and trust the relationship between the thermistor and the control board is rooted in German engineering.


Have you ever had someone tell you to move your wall thermostat at home around the wall until the house feels more comfortable? You might buy a higher quality thermostat with an anticipator, programming time etc. The Control Board in these RV frigs manages all that so your thermistor is simply a temperature sampler in the box.

On our RMD I see some impressive engineering as compared with the RML. Maybe they farmed out the RML ... something went wrong there ... On the new RMD I'm testing the range on 1-5 and it's looking correct. Good thermistor. Moving on to fan(s)!

Time spent on fans and modifying air flow to lower the temperatures around the cooling unit make a lot of sense to me. And insulation is a little icing on the cake.

[MyronL]

Bob the funny thing is I thought I indicated it was for the RM8551 when I ordered. BUT...But-But-But... cannot find my email documents so, not absolutely sure about that.

When the replacement arrives we will have been back from a 1 week trip... that should give me a good rationale for putting it in or not putting it in the fridge.

also....what Klem said, especially his very last two sentences.

[Tonny LR]

"Time spent on fans and modifying air flow to lower the temperatures around the cooling unit make a lot of sense to me. And insulation is a little icing on the cake quote by Klem".

Thanks for the expert advice

[Kountrykamper]

I have not found a need to change my sensor. I pulled my sensor out of the mounting bracket to get it away from the coil and out in the air. Before I moved it 3 bars would get me around 42 degrees. With the sensor in this position and not sensing the coil temp but now sensing the air temp instead the fridge runs around 37 on 3 bars. No other changes or mods as this was done long after I had long finished my mods. It's not like moving your thermostat to different walls at your home and still sensing the same air temperature. You sensor is no longer sensing the coil temp but now is measuring the air temp.

Also mine runs runs 31-32 on 4 bars and 28-29 on 5 bars. Yelp I did say 28-29 degrees.

Thanks Alf!

[Klem]

Originally Posted by Kountrykamper

Also mine runs runs 31-32 on 4 bars and 28-29 on 5 bars. Yelp I did say 28-29 degrees but it takes all the other mods I did to get there.

Thanks Alf!

I'd say you now are justifying buying the adjustable thermistor to move that curve up above freezing. Monitoring the freezer temps may confirm.

You might ask the vendor to recommend a location (I think it's on their install instructions?) for optimal coupling.

[Kountrykamper]

I can move the curve up from freezing just by putting the sensor back on the coil. I like having the lower curve and extra reserve for weather above and 95. If it's really hot out I set ours to 4 bars at night and bring it down to 31-32. Most things won't freeze at 32 unless it stays they for a long time. Exception is lettuce which I have done a couple times messing around with the fridge so now it gets put in an insulated bag.

With the 12 volt interior fan on it keeps the air moving over the sensor and does not let the fridge cycle as much and the fridge temps more even. They will stay within 1 degree with the fan running and helps draw the heat out of anything warm you may put in. I'm a firm believer that you need some kind of interior fan even if its one of the battery operated ones. Mine is very small and low air volume.

[Tonny LR]

Hello Tom,
May I ask how do you locate the 12V wire which is to be connected to the computer fan without removing the refrigerator. Where do your find the channel to thread the 12V wire into the inside the refrigerator?. Do you have to drill a hole? Thanks.

Tonny LR

[Kountrykamper]

Just push it through the hole where the sensor wire goes through and pick up 12 volt on the back of the fridge. I run one wire back over the top,of the fridge to a switch I located in the upper cabinet which can be done by removing the control panel and using a yard stick or something to push it under the rubber seal. Be careful you run all wires away from the boiler some so the wire does not touch anything hot. It all can be done without removing the fridge.

The battery fans work ok I just wanted something a little better I could control. Somewhere I posted the part numbers for the fan and guard but if you need them I could find them again.

[Tonny LR]

Tom,
Thank you for the instructions for installing the refrigerator cooling fan. I will try to search for the post. I appreciated your help.

Tonny