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…
- Purchase a common 5mm (10mA) LED (light emitting diode) from any electronics store (eg Dick Smith Electronics or Jaycar).
- Locate the controller box for the compressor (see the photo)
- Identify the terminal labelled ‘D’ (the D stands for diagnostic)
- 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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