Refrigerator fans

RodeWorthy · 03-17-2008, 12:37 PM

This question has been covered before but I am having a problem with Search.

I am experiencing a problem with Dometic RM3962 refrigerator not cooling well. I have checked the fans and presently they are not running.

Do the fans run all the time or are they intermittent?
Where is the fuse located for the fans?
Do you move the sensor up on the fins to make the cabinet colder or do you move the sensor down on the fins to do that? I have seen both up and down touted in other forums. Experimenting tells me that moving it up cools more but others are telling me it is down.
Is this a myth? Why doesn't Dometic mention the sensor in their manual?

RodeWorthy · 03-17-2008, 02:52 PM

Well, I posted these questions too soon. Duh. I found the fuse, tucked inside the wire harness. It helped when I put my glasses on :( The fuse is still 1A but it is good. Are we still changing these out to 3A?

The fans are intermittent and are controlled through a thermal switch which is not calling for them to run. The thermal switch is attached to cooling fin on the cool end of the heat exchanger behind the outside top panel. The fin it is attached to is not making good contact with the tube and thus does not have good heat transfer to the switch. I am doubtful it will ever call for the fans to run unless that thing gets a lot hotter than it is. I am considering by-passing the switch and forcing the fans to run to see if it makes a difference.

I am currently running on level 4 of 5. The freezer is now running just a touch over 0 degrees but the lower cabinet is just over 40 -not low enough. Before this problem began we were running on 3 and we had a well balanced refrigerator cooling well below 40 degrees. The problem started sometime after we defrosted and cleaned the refrigerator. It was working great before that. It has slowly deteriorated to the present state.

I will move the sensor down to see what affect that has. Right now it is near the top of the fin on the right end of the heat exchanger. After examining it I have a hard time believing its position has any affect. The sensor does not contact the fin. It just sits in the plastic carrier.

I have the A/C on today so the ambient is lower than yesterday.

I also found some of the insulation behind the heat exchanger at the outside top panel had fallen down and cut off good air flow. I have duct taped that back into place.

ponch · 03-17-2008, 06:24 PM

There is another fuse that is located behid the black box, in you outside compartment.

Ponch

Charlie and Sue · 03-17-2008, 09:48 PM

Rodeworthy,
I also had trouble keeping the fridge cold enough,I moved the thermal sensor from the fin at the outside of the unit and wire tied it to the evaporation tube just below the cooling fins, they run more often but my fridge is much colder on the three setting than it ever was. The set of fans lasts for 10,000 hours of running, about a year or two. We full time so the fridge is on always. At first the thermal switch was defective so I had to replace that some time ago. I buy replacement fans from Radio Shack for about $40/set, easy to install from the top cooling grate outside, four screws. I did replace the fuse with a 3A and haven't blown one since. Watch out that tube gets extremely hot.

Good Luck, Charlie and Sue

Motor31 · 03-18-2008, 10:08 AM

When you mention the temperature sensor on the fins, are you talking about the one inside the fridge in the cold area? If so we have ours on the outside fin but about half way up from the bottom. Previously it had been higher but then the fridge didn't cool that well but the freezer did.

As far as the outside fans are concerned, heat rises so doing what you can to help it flow is good. Just make sure the air is going up over the outside coils. On our rig the fans are on top and pulling air through them.

We also have a couple of those small battery operated fans inside the fridge to help circulate the air inside there. That helped equalize the temperature inside.

Mikey · 03-18-2008, 12:20 PM

There's a plastic drip tray under the fridge fins. The thermometer sensor wire runs BEHIND the tray (right side). We had a similar problem. Moved the tray out just a bit. Works better now.

rdunk · 03-18-2008, 05:31 PM

Most of us have had problems with our Dometic fridges. Right off the bat we blew fuse, and learned the 1 amp needed to be replaced with a three amp. But mostly it just did not cool well enough, and then when it did cool pretty good, it would frost up quickly, and need to be defrosted. Then couldn't hear the fans running, and figured the heat sensor was bad, and replaced it. No change. Had a technician test the sensor using a heat gun. Yes, the fans came on at the proper temp. of about 150 degrees, and went off at about 130 degrees. The tech confirmed the on/off temps with Dometic. The entire cooling unit was replaced, with no noticeable change. A technician did replace the "thermister", which is the inside temp sensor. No noticeable change.

You can check the thermister, by unplugging a small white (on ours) connector from the card on the lower rear of the fridge. An unplugged thermister defaults the fridge to run on high. If the fridge runs colder with the thermister unplugged, then it may be a bad thermister.

I had moved the thermister a number of times during all of this. Finally one day, a little exasperated with the fridge, I moved the thermister nearly as high as it could go on the fin - the top of the plastic sticks up about 3/4 of an inch above the fin. I don't know whether just moving the sensor that far up caused a change, or maybe it is the first time the thermister (small contact sensor on the end of the incoming wire) actually made contact with the metal fin FOR THE FIRST TIME.

But since that time, the fridge has worked great (for an RV style fridge). Running on #3, right now, with the outside temp at 73, and the fridge having some use during the day, it is at 39 degrees (if the outside temp were 15 degrees higher, it wouold still be at the same temp. Over night at this setting it will go down two or three degrees from that. On #5 it will go to freezing overnight. If we put a lot of stuff in the fridge after going to the grocery store, we will turn it up for a quicker cool-down. For overall, #3 works best for us, for not freezing up the fins.

As most know, a common "inside the fridge fan" does helpthe fridge cool better. I am made aware of that every time the fan batteries deplete, and the fridge temp goes up a little. :lol:

Now over the time, I have found that after a good defrost, it usually takes several days for the fridge to get back to a satisfactory cooling temp.

Hope this is helpful!

RodeWorthy · 03-18-2008, 09:25 PM

Thanks for the info folks. You people are the greatest.

Ponch - In my unit the circuit board cover is gray. The cover indicates there are two fuses behind it, 3A and 6A but I found only one - 5A. It is good. Thanks for pointing it out.

Charlie and Sue - Thanks for the info on the outside temp switch that controls the fan. I tried shorting across the switch to simulate closed circuit and the fans did not run. I have no indication that they ever run. I will try to heat the sensor with hair dryer tomorrow as a test. I like your idea of moving the thermal switch and will do the same after I verify it is working. Yes the tube is hot -but the fins are not. I have to believe those fans should be running.

Mike - I actually referred to both the outside and inside fins. See comment above on the fan control for the outside. For the inside fins, I know the sensor got knocked off during cleaning. I may have repositioned it wrong. I have now placed it so it is next to fin and surrounded by plastic carrier. I think this was/is a lot of my problem. No guarantee the sensor is touching the fin but at least it does not have a piece of plastic in between now. We will see what happens. I was in CW looking at those battery fans two days ago. Wish I had bought a couple. I believe WalMart carries them too. I think you have verified that moving the sensor down will increase the cooling in the lower cabinet. The freezer is working great -presently at -2F. BTW the fans in my unit are slightly higher than half way between the two outside openings.

Mikey - Thanks for the tip on shifting the tray. I am trying that too.

Robert - Good info. Thanks. I located the sensor connector to the thermistor. After my experiment with repositioning the sensor I will pull the sensor if problem persists. Your observation is the same as mine -does the thermistor actually touch the fin? Is it supposed to? I have to believe this is a control issue. The freezer works great -just can't get enough of that cold into bottom cabinet.

billr · 03-18-2008, 10:40 PM

Don,

My cooling fan thermostat failed so I removed it and wired the fan's (added a second one) to two seperate switches inside the cupboard next to the fridge inside trailer. Also increased the fuse size. I now contol them myself. None, one or both as needed by outside temps. Works well. Still the fridge temps are not brilliant. I will look at some of the other suggestions here in this thread to try and improve it.

Cheers,
Bill

Carny Bill · 03-19-2008, 09:20 AM

We have owned 2 dometic frig's in an 04 and 06, both have been very marginal, not cooling well and frosting up frequently. This last one does not seal well even when a complete new door was installed.

rverdlm · 03-19-2008, 09:23 AM

FWIW, I just had to replace both my fans. To test them I wired them direct to 12V power and they would not start. If I started them by hand they would run, but they still wouldn't start. Even without the fans the fridge stayed cold on a setting of 3. We have the side by side fridge and the frige stays pretty frost free, but the freezer needs to be defrosted every couple of months.

RodeWorthy · 03-20-2008, 06:58 AM

This refrigerator worked well for 4+ months on level 3. The lower unit stayed cold in the 36 degree range as indicated on the LED panel and by thermometer inside the cabinet.

I believe it is time to call in Dometic. The LED on the refrigerator now reads 35-36 but the inside temp is about 46. This on level 4. That tells me the fridge thinks it is cold and does not attempt to cool further. The freezer is colder than it ever was -probably because I am now on level 4. This indicates cooling is working but control is not. I have decided not to attempt any changes since the unit is under warranty.

I still have not figured out where that sensor on the inside fins is supposed to sit. Maybe Dometic can clue me in. Disconnecting the sensor at the circuit board did cause the LED read out to go to 60 which is an indication temperature is above operating range as Robert has stated. I did not notice any improvement in inside temperature with the sensor disconnected. The LED also flashed E2 alternately with the 60 temp reading. The error indication is understandable.

The fans on the back of the unit do not run. There is 12V across the temperature controlled switch. I don't know if they ran before when the unit was working well. The fans still do not run when the switch is by-passed. Eventually improvements will have to be made to ensure the operation of these fans but I will let Dometic have at it first.

It is interesting to note that Dometic states that a unit parked a long time without moving and not level can result in liquid ammonia accumulating in the evaporator tubing causing restriction or blocking of the circulation of the ammonia gas. Maybe I have been sitting too long and need to hit the road. My unit is level. We have been in SW Fla for over 3 months with no significant moves. Scheduled to be here 10 more days but may have to cut that short due to this problem. Back to living out of a cooler. Yuk.

So I am off to talk with Dometic (sigh)....

Charlie and Sue · 03-20-2008, 09:18 AM

If you're still under warranty then take it to any RV dealer that Doubletree authorizes and they can take care of it. Turning Wheel RV is a doubletree dealer up here on Rte.27 in Clermont Fl.. I had a dealer here in Leesburg replace mine the first time under warranty. If I remember the thermal switch cost me adout $27.00 from Dometic.Good luck.
I'm having trouble with my dual pane windows getting cloudy on our 05 MS, ever have that problem? The rear window is going bad, should be costly, have emailed Herh but no reply, figures, only three years old. I guess we will try DT but don't have much hope.

Take care, Charlie and Sue

CherriandBob · 03-28-2008, 09:33 PM

Rodeworthy
We were wondering if your frig problems got any better. We had trouble with ours last year when we went to Branson for the rally. The frig had an inside temp of 53 degrees. Had to throw out a lot of food. We had a tech come to the campground. In the outside compartment for the frig he put in an aluminum shield in the top to help hold up the insulation and to direct the airflow from the fans out the top vent.Then he wired the two fans up to a switch so they could be manually controlled, but this hasn't really helped either. When in warmer weather it doesn't matter if the fans run or not, the frig will be around 40-42 degrees and the freezer didn't stay cold enough to freeze ice cream. We did find that if you unplug the thermister the frig will drop to around 27 not sure how the freezer did, but not happy with the frig and will be contacting Dometic for input. Good luck.

Bob and Cherri

rdunk · 03-28-2008, 10:53 PM

Quote: " We did find that if you unplug the thermister the frig will drop to around 27 not sure how the freezer did, but not happy with the frig and will be contacting Dometic for input".
.................................................. .......................................
On the basis of the above, that means the cooling unit is certainly working, which is a very very very good thing. Also, it shows that either the thermister is not attached properly to the fin, or the thermister is defective. This (a thermister problem) is something easy and cheap to fix.

If you haven't done it already, slide the thermister as high as it will go on the fin, and see what the temp does. Then, if that doesn't help, make sure the end of the thermister wire under the plastic is touching the fin. If that doesn't get the fridge to cool, it must be a bad thermister. It is one of those two things that resulted in our fridge to begin to cool properly.

Nope, not an expert, but, "been there and dun that", with Dometic, as many others here have!!

Good luck!

CherriandBob · 03-29-2008, 10:48 PM

We believe the thermister was replaced the last time we had it in for repairs. This new thermister doesn't look like it would even allow the wire to touch the fin. It looks like it is made to hold the wire away from the fin. It is offset and holds the wire away from the fin. Currently we are trying to just lay the wire in the tray just to see what that does. We have tried placing it at the top of the fin. That is where the tech placed it. We are sure this is a new thermister because there was a piece of wire left from where it was fished through and new wire ties. Thanks for any input/

Bob and Cherri