Caravan fridge problems – how to fix the most common faults

by Collyn Rivers

Pic: Original source currently unknown.

Q. My caravan fridge works fine whilst on 230 volts, but not on 12 volts when we free camp. How can I can tell for sure if the fridge is faulty?

A. You can be 100% sure if you remove the fridge. Then see how it performs standing alone in a garage at much the same temperature.

Poor installation

Q. A friend says you emphasise in your book (Caravan & Motorhome Electrics that most caravan fridge problems are due to faulty installation. How has this come about?

A: A probable 95% of caravan fridge problems are because they are poorly installed. There are two main types of caravan motorhome fridges: 12/230 volt compressor, and 12/230 volt/ LP gas (so-called) ‘three-way’ fridges. Both suffer from poor installation. Some RV makers and many self installers do not understand how fridges actually work.

Fridges do not make cold. They are simply pumps that moves heat from where it is not wanted – to where it does not matter. You must have a cool air inlet at their base. You also need to direct that cool air through the fridges cooling fins. Rising hot air must easily exit.

Ventilation is vital

Ventilation is totally vital for three-way fridges. This only too often insufficient. Some have none at all. Unless ventilation is provided as specified (and illustrated in Caravan & Motorhome Electrics) they have no chance of working correctly, on either electricity or gas. See below if the fridge works on gas and 230 volts, but not 12 volts.

Many caravans now have access to 230 volts, so they use this most of the time. Here, cable size can usually be relied on to be fine. Use much heavier cable if it runs on 12 volt solar/battery power. The required cable, however, is costly – so is rarely used. Current draw on 12 volts is very high. It is only feasible from a vehicle alternator, and short lunchtime stops from battery power.

Q. I know caravan fridge 12 volt fridge cable is usually too small. How heavy must it be?

A: This depends on the distance from the battery – it should not exceed two to three metres. Errors are caused by there being several ways of specifying cable size.

When specifying cable size, makers of electrical stuff either quote the cross-sectional area in square millimetres, in AWG or B&S. The latter are identical for all practical purposes. For most electric compressor fridges, the minimum is 4 mm² (AWG 10), but 6 mm² ( AWG 8) is preferable. Three-way fridges draw from 12-30 amps. These really need 8 mm² (AWG 7) unless the distance is less than two metres (when 6 mm² is fine).

Auto cable size

Q. I hear there is a problem with the auto cable sold in auto parts and hardware stores.

A. Auto cable is usually just fine. But, for reasons that defy sanity, auto cable makers use similar ‘numbers’ as above (e.g., 4 mm, 6 mm) to imply something totally different.

Auto cable ‘4 mm’ is not 4.0 mm² – it is the overall diameter of the cable including its insulation. That rating is the size hole you can push the cable through!

Worse, auto cable insulation thickness and type varies from maker to maker. Most 4 mm auto cable is anywhere from 1.8 mm²-2.0 mm². Most 6 mm auto cable is 4.6 mm². The reason why so many fridges are affected is because that 4 mm² and 6 mm² cable are the sizes most commonly specified.  Be aware that even if you ask for (say) 4 mm² cable what you almost always sold is 1.8-2.0 mm² auto cable. Many people fall into this trap as few vendors know there’s a difference. (The square mm size is, however, usually shown in the cable’s specification.)

Caravan fridge – current ratings

Q. My three-way caravan fridge draws 25 amps. It is connected to the tow vehicle battery by ten metres (total for twin conductor) of 35 amp cable – yet barely works. A friend has your Caravan & Motorhome Book (that has a lot about caravan fridge problems). He says the cable is much too small. How can this possibly be? It’s already three and a half times the necessary current rating!

A.  Current ‘rating’ is mostly misunderstood. It is not a current carrying recommendation but a fire rating that relates only to the current the cable can carry before its insulation begins to melt. The rating has absolutely nothing to with voltage drop. The most commonly used ’35-amp’ cable can be as small as 4 mm auto cable (1.8 mm²)! Ten metres of this introduces a massive three volts drop. That fridge will barely work at all. The minimum you need is 10 mm², over seven times the size.

You need to locate that battery in the caravan, charged from the alternator by a caravan-located dc-dc charger. See: dc-dc charging. Still use proper size cable. (You owe your friend, and that fridge, one considerable apology!)

About the author

Collyn Rivers is an ex motor industry research engineer who switched careers in mid-life to write and publish technically correct books in plain English. They cover the caravan, motorhome and solar areas.

The ‘overall’ ones are the Caravan & Motorhome Book, and the second edition Camper Trailer Book. Electrical issues are covered in Caravan & Motorhome Electrics, solar in Solar That Really Works (for cabins and RVs) and Solar Success (for home and property systems).