Diagnosing Motorhome and Caravan Electric Fridge Issues


If you have read any of my other articles relating to caravan and motorhome refrigeration, you will know that I am a big fan of electric compressor fridges (as opposed to gas or so called 3-way fridges).

While these compressor based fridges are extremely robust and reliable, of course things do sometimes go wrong. In this article I would like to explain how to diagnose and resolve the most common issues with mobile electric fridges.


FAULT – Excessive build-up of ice in the fridge or freezer.

This problem is almost always caused by seal related issues. The door on the fridge needs to form a near perfect seal – if air is allowed to enter and escape two things will happen, the compressor will run far more than it should and lots of additional moisture will enter the compartment. This results in a large build-up of ice on the cooling elements.


FAULT – The fridge is getting too cold.

While the thermostat knob is normally located in the fridge compartment, the actual sensor is often located in the freezer. If the fridge is getting too cold it is likely that the freezer is not cold enough (and the thermostat is keeping the compressor running). Look at the seals on the freezer door. It is also possible that you have just loaded the freezer with a lot of food to be frozen and the compressor is doing its best to do this for you.

FAULT – The fridge/freezer is not running or not getting cold.

There are a number of issues that can cause this. Follow this procedure to determine what your issues(s) are…

1. Check the voltage at the fridge. Using a voltmeter attached to the wiring as close to the fridge as you can (preferably right at the + and – terminals of the fridge controller).

If there is no voltage – check the fuses and the wiring.

Leave the voltmeter connected for some time. If the voltage suddenly drops as the compressor is trying to start this suggests a fault in the low voltage power cable OR a flat battery. Danfoss compressors have an automated low voltage cut-out that is designed to stop the compressor when the supply voltage falls below a particular point (by default this is cut-out at 10.4v (22.8v) and cut-in at 11.7v (24.2v)).  See the section below – using the diagnostic LED.

2. Check the thermostat – you can do this by shorting out the thermostat (terminals T and C on the Danfoss controller). If the compressor starts when these terminals are shorted – you have a thermostat issue.  Thermostat are not expensive and simple to replace.


Using a Diagnostic LED

The Danfoss compressor controller is a very clever device – it has more than its fair share of intelligence and even includes a function to tell you what is wrong if it has an issue. Unfortunately most fridge manufactures ignore this diagnostic ability and save about 50 cents by not implementing it.  You can add this function to your Danfoss based fridge very simply…

  1. Purchase a common 5mm (10mA) LED (light emitting diode) from any electronics store (eg Dick Smith Electronics or Jaycar).
  2. Locate the controller box for the compressor (see the photo)
  3. Identify the terminal labelled ‘D’ (the D stands for diagnostic)
  4. Using a push on connector (spade terminal) connect the LED to the D and + terminals as shown in the diagram. (The long leg of the LED connects to the + terminal.)

Now that you have the diagnostic LED in place, the controller can tell you of its problems. It does this with a kind of Morse code … it flashes the LED a number of times then pauses. BTW – it is fine to leave the LED connected to the controller – I have extended the wire and have the LED for our fridge visible all the time, it makes a great early warning system.

  • 1 flash = Battery protection cut-out. The controller has detected that the supply voltage at its terminals is too low. This either means that the battery is too flat, the wiring is faulty OR the wiring is not heavy enough for the fridge.
  • 2 flashes = Fan over-current cut-out. The fridge has a fan that is designed to cool the electronic controller. If this is obstructed it will try to draw too much current and cause the unit to stop with this error code.
  • 3 flashes = Motor Start Error. This is often caused by stopping the fridge (un-plugging it) then quickly powering it up again. When the compressor stops high pressure gas remains inside the compressor and this must be allowed time to dissipate before trying to start again. Normally waiting a few minutes will clear this error – if it does not, it is time to make visit to the local fridge tech.
  • 4 flashes – Minimum motor speed error. This is a fault with the refrigeration system and will require a technician to resolve.
  • 5 flashes – Thermal cut-out of electronic unit. This error suggests that the electronic controller has exceeded its safe working temperature. This might be caused by a faulty cooling fan or poor ventilation. It is NOT that the compressor is too hot.


Of the errors listed above, by far the most common in motorhomes and caravans is the single flash – battery voltage issue. I have seen more of these faults than any other and it is normally caused by a simple flat battery. If you do not (properly) monitor your battery state, this is the most likely reason for your fridge misbehaving and condemning you to warm beer.

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33 Responses to “Diagnosing Motorhome and Caravan Electric Fridge Issues”

  1. Fred Says:

    hi Gavin n Tracey..just don’t know how / where you guys get the time to pass on your experiences n travels, very inspiring and interesting..following your building with much interest…your fridge info. posted recently is very timely for me, as I have just replaced the thermostat [ Renco VT9 2 door ] in my 220L Coolmatic..problem is, it will not switch off, n came down to -3 degs in fridge, which contained a doz cans of beer, and bottles of water in freeezer,which froze solid..I connected the compressor lead to term 4, the thermostat lead to terminal 6, the light to term 3, and the green cable to thermostat body earth…I pushed the tube sensor in the side tube housing at various depths, as i’m not sure what depth to insert it..I think the sensor is not getting cold enough to switch off, or the new thermostat is faulty…On advice, I tried to attach the sensor direct to the evaporator panel at inside rear of fridge, n still it runs continuously..A Waeco fridge mechanic told me that I should only connect to terminals 3 and 4, but that didn’t work either, nor did the light!!…your thoughts would be appreciated…Thanks, Regards to you both…Fred n Kathy

  2. Hobo Says:

    Hi Fred,
    The thermostat is just like a switch – it should have only two wires connected to it. They should connect to the terminals marked T and C on the danfoss controller (so check the colors of the wires on these terminals and use just these two on the thermostat.
    With the fridge running, remove one wire from the thermostat – the compressor should stop. IF it does not – the wiring is wrong, if it does the thermostat is faulty or incorrectly installed.
    The fridge you have started life as a Westinghouse household fridge – Waeco took the fridge and converted it to low voltage using a Danfoss compressor – thus the wiring is color coded for 240v usage (hence the green wire not being an earth).
    Feel free to phone me (see contacts page) as I may be more help by phone.

    Gavin (Hobo)

  3. Fred Says:

    Thanks for the reply Gavin, I previously did connect only 2 wires, but wil do as you suggest re the thermostat wire being removed to see what happens…I will do it this weekend, and give you a call with feedback…Cheers, fred

  4. Bill Says:

    Our caravan has 12 volt house lights. When connected to 240 volt supply, 240 transforms to 12 volt. Is the transformer using power, if all lights are switched off?

  5. Hobo Says:

    Short answer = yes, if a transformer is powered, it is consuming current even when there is no load.

  6. Marken Says:

    Hi Gavin. I have many questions regarding caravan electrics so will endeavour to ask them in connection to the relevant articles. Just purchased a second hand Goldstream caravan and used it in hot conditions in Vic. The 3 way fridge did not perform well (as previously reported in another article) and I am wondering if it can be converted to 12 volt by adding a Danfoss compressor by a refrigeration expert?
    This leads me to another question regarding Danfoss compressors. I have heard they the Danfoss compressors that are available are now made in China and are failing at a rapid rate. Do you have any knowledge of this? Can the original German compressors still be obtained?

  7. Hobo Says:

    Hi there,
    Converting an existing three way fridge to compressor is sadly not practical. The internals are just too different.
    The compressors made in china are not Danfoss – they are (like many Chinese things) just a poorer quality copy. That said, I have not heard of any reports of massive number of failures. I have a small Waeco fridge (with a Chinese compressor), that has been used as a freezer for months at a time and as a drinks fridge – it is now almost two years old, have never been turned off and is working fine. I also have a friend who made his own freezer from a BD35 Danfoss compressor 8 years ago. The BD35 was always too small for the size of the freezer compartment and thus the thermostat NEVER turned off. After eight years of continuous running that little Danfoss compressor is STILL Running! That is very impressive.
    To answer your question – many Australian fridge manufactures are still using genuine Danfoss compressors.

  8. Neil Says:

    Experiencing ‘shut down’ problems with 220L Waeco – 2 years ago original fan was faulty and was replaced with ‘second hand’ Engel by Waeco Service Agent. The compressor shut down problem was evident at time of original fan problem! When weather is cool frig usually shuts down without much problem , but in hot weather the compressor has lots of difficulties, stop, start,stop,start……….. Have now discovered that replacement fan is 24v and hardly pushes out any air to control box/compressor! Am about to order 12v waeco fan. Would this ‘cooling fan’ be the problem or the frig has major problems. ( cooling /freezing has always been excellent)

  9. Hobo Says:

    I would be VERY confident that your issues are related to the fan. The danfoss controller is designed to control and power a fan up to a certain current draw. Replacing the fan with anything other than the correct one will certainly cause the issues you describe. To prove this (and the service agent should have done this) you can attach a diagnostic LED to the danfoss controller – this will immediately display the error code for “Fan current beyond specifications” .

    I hope this helps.

  10. kovu Says:

    got problems with my coolmatic waeco 110 fridge , freezer only gets cold and fridge gets slightly cool , so the compressor runs continuously , the LED fault light is not on , could you please help

  11. Hobo Says:

    Sounds like a gas issue to me. More info about what you have tried and tested might help confirm this. If the compressor runs continuously and the fridge does not get cold, it is unlikely to be an electrical issue.

  12. Andrew Says:

    G’day I have got error code three coming up is this because too much gas, it is a new fridge

  13. Hobo Says:

    It could be excess gas, but this is unlikely. If this error is constant, it could mean that the compressor has a mechanical issue (the rotor is jammed). If this error is intermittent, it could indicate an electrical fault in the external wiring (Or that the rotor is jamming).

  14. Andrew Says:

    Will the fault codes on the compressor only come up when there is a fault or can you get logged codes out? What I’m trying to get at is ruling out external wiring, but will test when code is alarming. It does run a LCD screen with its own codes so it is possible it could be the wiring thanks for your reply

  15. AllBlackFan Says:

    Hi, Have a waeco cf60 verb.
    (1) I would like to know how long you would expect it to take to bring down the internal temperature to -18c I suspect mine is not running on turbo. Otherwise it seems to run fine but probably takes a couple of days to reach a digital displayed -18c @ 16c ambient, 3/4 full of water bottles.
    My understanding is the displayed temp should drop quickly even if the bottles do take time to actually freeze.
    (2) Is it simple to rig up a trim pot’ to manually adjust the compressor speed? Bypassing the waeco controller. I have seen some third party products for doing something similar but they seem outrageously expensive for what on the face of it looks to be a simple task, or am I missing something? TIA for any thoughts.

  16. Hobo Says:

    I would expect the freezer to pull the temp down to around -18 in about 12 hours when full of bottled water.
    You can adjust the speed of the compressor (depending on the model of the controller) by changing the value of a resistor placed in series with the thermostat (ie between the thermostat and the ‘C’ terminal.
    Values are as follows :
    zero ohms = 2000 RPM
    277 ohms = 2500 RPM
    692 ohms = 3000 RPM
    1523 ohms = 3500 RPM

    This is for the 101N0210 and 101N0220 controllers – if yours is not one of these you will need to check the values.


  17. Debbie Says:

    Hi have a waeco CF-60 VERB That will not run on 240 voltage it starts and stops but will run ok on 12 volts not a problem can you please offer any advice would be most grateful it is six years old had very little use

  18. Hobo Says:

    Most likely to be a fault with the ac adapter or perhaps a the low voltage cable from the adapter to the fridge.

  19. simon and jen Says:

    hi gavin I have found your information very helpful .we have a waeco hdc220 up right fridge. will the fridge run ok without the controller lights volts connected part no4441600017 .the fridge is running but I don’t know if the compressor is cycling or just constantly running . we have the controller on order but it has not turned up yet the van copped a power surge 12 months ago I have been chasing my tail ever since any help would be greatly appreciated9

  20. Hobo Says:

    I’m not 100% sure what you are asking here. If you want to know if the fridge can operate without the compressor controller, then the answer is no, I am afraid that the compressor will not run without the controller.

  21. simon and jen Says:

    thank you for your quick reply your help is appreciated

  22. Merv White Says:

    Hi, I have a 160l itre coolmatic compressor fridge in my van. The freezer works ok but the fridge compartment doesnt cool at all. Can you give me idea of the problem.

    Regards Merv

  23. Hobo Says:

    Sorry, I’m not going to be of much help with this other than to say that it is likely to be a gas issue and almost definitely not an electrical one.

  24. Brett Says:

    I have a GD30FDC, so the controller box is a little different and not sure if the led testing is the same.

    Anyway with a little investigating, and bridging the thermostat terminals, my fridge tries to start and the cooling fan kicks in. But when it does the volts drop quickly below 11v and the fan stops (assuming the compressor also does if it even gets a chance) … give it a few moments and it will attempt to start again.

    My power supply is a 12v battery that is capable of running other things like floro lighting etc. I have also tried connecting up a 12v battery charger at the same time so it is delivering 14v and get the same results.

    Just now I tried connecting just the fan. The fan kicks in and runs for about 15 seconds and then suddenly the volts drop below 11v and then will not run again until it has a few moments ans repeats.

    So is it likely that I have a faulty fan?

  25. John and Jose' Says:

    Hi Gavin
    I have a Waeco upright 220L fridge freezer that I bought secondhand for a van I’m building, the seller was upgrading and I’m currently discovering why.
    When I first turned the fridge on the freezer worked but not so the fridge, from my reading on here I’m putting that down to a gas issue although I have found a drain hole at the bottom of the fridge directly above the compressor is open and venting directly to a hot area.
    Inspection of the compressor and controller revealed the fan disconnected and there was a disconnected 50V Lelon capacitor mounted above the controller, the primary black wire to the controller had partially burned through the insulation, all of this is telling me that the fridge has been giving trouble and possibly poorly installed from the start.
    I removed the capacitor, reconnected the fan and installed a red led on long enough wire that it will sit permanently atop the fridge for future reference, I placed a battery at the back of the fridge to eliminate voltage drop and connected it.
    The compressor started immediately as did the fan, the LED gave no error message, my concern is that the fan runs constantly from start up, is that what it’s meant to do or is that a fault?

  26. Hobo Says:

    This sounds like a gas issue to me (and I’m no expert on refridge gas issues)!.
    The drain hole is normal – it discharges on top of the compression – this is to allow the water to evaporate.
    Yes – the fan does run whenever the compressor runs.

    If the compressor runs but the fridge does not get cold – its a gas issue.

  27. Hobo Says:

    I would look closely at the power supply – if it can not supply enough current to run the fridge this is exactly what would happen.
    Run it from a freshly charged car battery – if this works, the issue is with the power supply.

  28. John and Jose' Says:

    Hi Gavin Thanks for your reply I have tested it as you suggest so will now have the gas checked.
    I’m currently at the kitchen stage of my van build and have located the fridge in an alcove next to the ensuite, because space is tight I allowed roughly a 35mm gap each side of the fridge but I now realize that’s not enough so will move the wall to give 50mm clearance, Jose’ will just have to make do with a bit less kitchen bench space.
    I have located my solar gear and battery bank under the lounge on the opposite side of the van which will require 9.5 meters of 12mm cable (Waeco chart recommendation) which is both expensive and heavy. I will have 240v available already by the fridge so am wondering if my best alternative might be to use a Waeco 240v rectifier designed for this fridge which should both cost and weigh less while providing 24v power.
    Your thoughts please. Cheers J&J

  29. Hobo Says:

    I would not use a 240v converter. Rule one is “Always run appliances from the vehicle native voltage where possible). The reason for this is that each voltage conversion has losses – so 12v -> 240v via the inverter = about 10% loss. THEN 240v down to 24v to run the fridge … another 5% – 10% loss (displaced as heat BTW). Nope, nope nope … run it from 12v.


  30. John and Jose' Says:

    OK point taken thanks. If I run a cable through and under the floor it’s only about 2 meters, is that advisable, legal etc? Cheers J&J
    PS your blog and followup is extremely helpful, thanks and please keep it up.

  31. Hobo Says:

    Yes, take the shortest route possible. Protect the cable with some (flexible) conduit under the vehicle.
    Check to make sure that the cable recommendations are listed in mm2. Over a distance of 2m, 4.58mm2 cable (called 6mm) should be fine.

  32. John and Jose' Says:

    Hi Gavin
    Have just picked the fridge up from my local Dometic repair agent, he found and repaired a pin size hole in a pipe and re gassed it, when I arrived it was sitting happily on 3c and the freezer was freezing, so I now have the fridge working as it should and a bonus diagnostic LED.
    Cheers J&J

  33. Phil Says:

    many thanks for this forum. I’ve read it from France because my danfoss bd35f fridge won’t start. After searching why it has started few times again and now stops definitively !?! I’ve done the diagnostic led : 5 flashes. Does it mean that replacing the electronic unit should resolve the problem or should it be an other piece that must been replaced ?
    Best regards

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