Dometic RMDX21 Fridge – Mods and Repairs

In our 2017 Essential Exceed Caravan we a standard Dometic RMDX21 3 way manual switching fridge/freezer. Very happy with it, though it has had a few issues over the last year, all so far solvable!

Slow running Drain:

5 sided Whipper Snipper cable

Firstly the drain was running slowly and dribbling down inside the back wall of the fridge. A quick check and yep, the drain hose was a little blocked with green algae (not unusual). A trick I learnt from our last fridge, grab a length of old whipper snipper line – this one is shaped like a star with 5 edges. Feed it down the drain tube and it pushed a lot of stuff out with it. Now fold in half (this one is quite thin), push it through again and then twist it around. I stuck it in the drill and ran that on a low speed for 20 seconds. Then pull the line through from the bottom and gently pour some warm water down the drain to flush out the last bits.

Click the image for an enlarged view

Over flowing drain tank:

Next issue, in very humid climate, the drain tank at the rear was not evaporating fast enough with the heat from the system (maybe we open the fridge too often?) and the tank had over flowed a couple of times. The tank should have some water in it so the drain hose is below the water the level, this stops warm air flowing up the drain hose into the fridge. So my mod was to add a short drain hose to the drain tank that runs from the upper side of the tank to the tube holder in the vent frame. Now if it gets more than 3/4 full it overflows to the outside and not all over the ply floor under the fridge.

The green hose used is a little bit of left over fuel line that came with the diesel heater. Hole is just slightly smaller than the tube so its a force fit. The heatshrink on the bottom is just to stop it flexing and keeps it in the holder better.

Click the image for an enlarged view

Drain for the drain


Freezer door jammed:

When running on gas, the condensation that builds up around the door locks can then freeze and jam the locks in place. This is why whenever you arrive at site you should disengage the locks, especially on the freezer door. On 240v power this is not an issue as the frame heater keeps the ice melted. On our particular fridge there may be a little more play in the hinge than others, because when the lock jammed up I was able to lift the latch end of the door about 3mm which was enough to lift it over the latch!

If you can not do this, you can use a hairdryer (if you have one) on the side of the door where the latch is to melt the ice. You can also turn on the Cabinet Warmer (read the instructions!) however this uses a fair amount of battery so you don’t want to run it too long when not on power.

Power issues:

Some of you may remember last year I accidentally turned off the main battery battery switch momentarily, but when it switched back on the fridge did not power up. Long story short – 24 hours later with the fuse removed it finally turned back on and I put tape over the switch to never turn it off again! I was thanking my lucky stars thinking the main control board was borderline terminal.

Anyway, fast forward 6 months and the fridge is now turning off randomly while driving and running on the car battery. The car power only runs the element in the fridge, the main computer is powered from the van batteries. So I check all wiring assuming a bad connection, and yes the main power leads (push on spade type connectors) are not very firm at all. So a quick squeeze with the pliers to increase the pressure and job fixed or so I thought. Next drive upon arrival the fridge was off again. It got to the point that closing the door firmly or moving stuff around in the fridge to hard would shut it down.

I played with the wiring and fiddled for ages with it turning off all the time but just not able to work out exactly what wire was causing it. Then when looking at the wiring closely (couldnt find a wiring diagram) I realised the thermal circuit breaker on the flue is actually inline with the incoming power, so if it failed, no power to the fridge at all. Close inspection found it was in a bad way with the terminals rusted and the rivets holding the terminals rusted as well, resulting in the terminals being quite loose. As a temporary fix I have pulled the connectors towards each other under pressure with some Velcro to stop them moving until I can buy a new one (currently in Lichfield National Park – not too many refrigeration repair centres around here!). UPDATE: Tried everywhere and ended up back at my favourites Everything Caravans… A new one is on its way.

UPDATE: replacement arrived, this is the old one after removal, you can see why power dropped out over bumps!

Old breaker after removal, can see it dropped power!

Stopping the bugs!

Our previous van’s fridge stopped working on gas at one stage so I had to take it down to get looked at. Turned out the lovely QLD mud wasps had decided to make a nest inside the flue system blocking the airflow. Time and $$ later I decided to put fly screen mesh over the vent to prevent this. Just normal fly screen, not midge screen as I didn’t want to reduce the airflow too much. I placed the fly screen over the back then dobs of hot glue to hold it in place. Working well. I did not do the same on the top vent as ours is a roof mounted upper vent and the screw holes had been filled with silicone so was too hard to remove in the time I had. Working on the premise that the wasps are too lazy to fly all the way down the bottom to make a nest!

Flyscreen over the vent

Lost the vent cover!

Well not us, but on our travels over the last year I have seen plenty that have lost the standard Dometic outside fridge vent cover. Ours is missing half of one of the lugs that hold the front in place and with it fitted over the ribbed aluminium it was always half popping off. Was thinking of a few options then saw what Bob had done and copied (Travelling Oz Our Way). Simply remove a middle screw from each end of the vent frame, drill a matching hole in the vent cover, refit the cover, put in the screw. Very simple and that vent cover is not going anywhere.

Auto shut off on car battery:

Our power feed from the car for the fridge is run directly to the car battery via a 50 amp auto resetting circuit breaker. I separated this from the 12pin trailer connector so I could unplug it when we stop for lunch somewhere to avoid running the car battery flat (the fridge draws around 13 to 14 amps continuously). Since I keep forgetting to unplug and was worried I was going to be stuck somewhere, I decided the easy way out was to install a VSR or Voltage Sensitive Relay. I picked up a 50amp KickAss branded one and installed it behind the fridge, plenty of room. Simply cut the main 12v fed from the car, put a ring connector on the cut ends and bolt them on to the VSR. A small black wire off to the negative connection and works like a charm. Once it detects over 13.2v for more than 15 seconds it turns on, when it detects less than 12.8v for more than 15 seconds it turns off.


The fridge seems to defrost itself fairly well when on 240v, but the freezer ices up and needs cleaning out once every 2 to 3 months depending on the humidity. Once the freezer ices up too much it stops keeping things cool. A quick job assuming you have a hairdryer on hand. Empty the freezer, remove the shelf, place a plastic tray under the fins and a towel to soak up the water, hairdryer on low fan high heat and aim at the first fin at anywhere you can see the aluminium. If you cant see any, pick the part with the least ice. Once that’s been in the heat for around 10 seconds the sheet of ice will simply pull towards you and off the fin. Repeat for all fins, stopping to clean up the ice and water as you go along. Takes no more than about 10 minutes and the ice cream hasn’t even had a chance to start melting!

That’s it for this post, any other great ideas you have for these fridges let me know and I will add them in!

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8 Responses

  1. Leonie and Glenn says:

    That is awesome thank you 😊

  2. George Stephenson says:

    Hey Dave, me again. I too am having issue with the fridge turning off while travelling, I had dent remove the feed from the 12 pin to it own Anderson until yesterday, but am curious with what I have found. The thermal circuit breaker is ok on my van, but when I measure the voltage at the fridge, with the fridge off I get 14.3, but once I turn the fridge on I only get 12.9volts. your photo “remove these frame screws” shows the feed at the top which is what I am talking about, how can the voltage drop, I would have thought the feed voltage was the feed voltage. I am really confused, any ideas Dave? thanks George.

    • Dave says:

      Hey George, that sort of voltage drop is pretty normal, the draw from a three way fridge is quite high when running on 12v for cooling, around 14 amps or so. At that current the voltage will drop along the length of the wire from the car battery to the van fridge, which is quite a log cable run. The 14.3v will be with no load looking back at the car battery, 12.9 when the fridge is running is quite normal and an acceptable level. Only way to improve that is to run heavier cables, however this drop won’t be causing any issues. Even dropping further will only reduce the cooling efficiency (which isnt great to start with on 12v for a 3 way fridge), but it wont cause it shut off. Worst case is the red light will be flashing if it drops too low. Is your fridge still shutting off? The only thing that will cause it to shut off is the thinner power wire that runs through that thermal circuit breaker – thats the power in to the controller board. If it loses power it will switch off. Mine also had poor connections on the spade terminals, at the back of the fridge, I notice that later models have changed over to screw terminals. Cheers, Dave.

      • George Stephenson says:

        Hi Ho Dave, I very much appreciated it mate, I will look further and test this weekend, I will take for a run as I haven’t been able to get more than 20 minutes with shut dow using the 12 pin plug, so with the fridge now connected Cars Red Anderson plug, I hope this help. thanks again, awesome support. regards George

  3. Mark Fitzmaurice says:

    Hi Dave, I like some of your ideas / recommendations, with the fridge vent has the lugs broken, it has about 6 screws holding it in,
    I have also fitted a cabin air filter to the inside of the vent to prevent dust getting into the van and past the fridge.



    • Dave says:

      Hey Mark, thanks for the comment! The vent on our fridge has about 6 or so screws holding the frame in place, the the vent cover itself was only the lugs on one end and sliding clips on the other. So when the lugs half broke there wasn’t much holding it in at all! I do like the cabin filter idea too – I used to work on Mobile Phone towers many moons ago and they had a filter material in the door vents to stop dust – a fibrous mat about 20mm thick – would have been perfect for that!

      Cheers, Dave.

  4. John says:

    Hi Dave, we have the RMDX21 fridge and works well on Gas for about 5 hrs. Then stops. Pilot light still lit, nothing flashing that there’s an error.. any ideas on what might cause this? I have cleaned the burner and got all dust/dirt out which helped the flame come back to blue, but cant seem to figure out why it won’t keep cold on gas? Thanks in advance

    • Dave says:

      Hey John, the fact that you have a nice blue pilot light that stays alight indicates all the gas functions are OK. I had an earlier model fridge that had the flu blocked by mud wasps that was stopping the system working properly – ever since I always put a fly wire screen on the vents.. Not sure if that will allow the flame to keep running or not though but worth checking.

      With no error light or beeps that would indicate all systems are operational (generally), then there are only really a few possibilities – one is the van not level enough (if on an angle the coolant doesnt flow properly); another is if the fridge is stacked in a way that is now allowing convection airflow – there must be space for air to flow in the bottom shelf area, up past the cooling fins and out the top and back down the front, make sure there is a gap between foods and the fins, foods and the door as well; another to make sure top and bottom outside vents are allowing airflow; and finally check that the fins on the outside back of fridge are clear (have had spider webs filling them at on stage that filled with dust and pretty much stopped air flow).

      It could be the thermostat, though generally that will set an alarm and also cause a similar issue on 240v

      As a first or last resort, try holding down the triangle with ! in the middle of it for 10 seconds or so if you haven’t already, thats the Gas reset.

      Its a bizarre one with no error lights or beeps and the pilot staying alight thats for sure! Please let us know what is was when you finally find it too!

      Good luck, Cheers, Dave.

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