THREE WAY TO COMPRESSOR FRIDGE CONVERSION – PART 1

We’ve been the proud owners of a 2007 Abbey Vogue 460 caravan since 2012. It’s our pride and joy, providing us with an unprecedented level of freedom to enjoy the Great British coast and countryside while also providing us with a comfortable base when attending motorsport events.

In the time we have owned the caravan, many ‘improvements and upgrades’ have been made. Multiple USB charging points and 12-volt outlets. Full LED lighting (including a self-built awning light), 120-watt solar panel from Sunstore Solar (self-installed) and chassis jacking points among many other little ‘tweaks’.

Many of these upgrades were made because we don’t want to be tied to mains electricity. This provides us with the freedom to use small CL sites (which can still be had for a fiver per night) which can be in much more convenient and picturesque locations than their larger counterparts. Many Caravan Club sites also have ‘non-electric’ pitches which can present a saving of over £50 per week. It’s not all about money, however. We don’t actually need 240 volts when we are away. We don’t take a TV with us, so the only ‘nicety’ requiring mains power would be the microwave that’s built into the ‘van (and that is something we can easily manage without). All of our other power needs are easily provided via 12 volts. Lighting is 12 volts. Phone, tablet and camera battery charging is via USB charging points and our laptops are charged using a universal charger that plugs into a 12-volt ‘cigar’ socket (this steps up from 12 to 19 volts so is more efficient than an inverter).

Not using mains power obviously means we have to use gas to power our Thetford N112 3 way fridge and this has been a continual source of frustration since we have owned the ‘van. It’s failed to fire up on gas (without warning) on numerous occasions, nearly killed us overnight (and probably would if we hadn’t had the foresight to purchase a digital CO alarm) and just wasn’t that ‘cold’. Because gas appliances have to be worked on my ‘qualified’ engineers, each time it failed, the van had to be taken in to have it repaired, costing in excess of £100 each time.

The last time it failed was the last straw. The burner had been replaced by a local service centre just over a year previously. In the interim, we had mainly stayed on sites where there was no choice in pitch, so we had been using the fridge on electric (despite what I said above, if we’re paying for 240 volts, we’ll damn well use it!). So, since the last repair, the fridge had been used for a total of 10 days on gas. Imagine the frustration when we rocked up for the British Touring Car Championships at Thruxton on an unseasonably warm May weekend just to find that the fridge would not light (well, it sort of lit but certainly not where it should have and the accompanying explosive ‘whoosh’ was quite disturbing). Net result, spoiled food before the end of the weekend and, more importantly, warm cider and wine!

There must be an alternative to this nonsense. Most caravan owners will know that 3-way fridges are (in my view) only partially 3 way. They will run on 12 volts but consume so much power that the circuits are designed in such a way that they will only operate when hooked up to a towing vehicle and the engine is running. This is a sensible approach because they would totally flatten a typical leisure battery in short order dictating a constant source of ‘generated’ power.

In our situation, it would be a godsend to have the fridge operating from 12 volts. As our leisure battery is charged via solar, the charge rarely dropped below 80% and even in mid-winter would be fully charged by mid-morning. We had spare capacity so it would make sense to use it!

On our return from Thruxton, a lot (and I mean a lot) of fridge research ensued. The more I read, the more I realised that the typical 3-way fridge is a particularly inefficient beast, using a passive, ‘absorption’ method of cooling. They are designed more for convenience than effectiveness and can rarely cool more than 15 degrees below the current ambient temperature and take ages to cool from startup. Domestic fridges, however, use compressed gas for cooling (the hum of a kitchen fridge is the compressor running) and are infinitely more efficient.

So, we needed a 12-volt compressor fridge. There are many models available, mainly from Dometic and Vitrifrigo. Replacing the existing fridge with one of these would potentially fulfil our needs but none of them would fit the space available. The main problem being the fridge is right over the wheel-arch so needs a stepped back towards the bottom. We could have purchased a smaller fridge, but this would have cost us a significant amount of chilling space and would mean filling the resulting void. This was all possible, but hardly ideal.

We were about to give up on the idea as nothing ‘right’ seemed to be available but then, purely by chance, I came across DIY cooling kits that are primarily designed to turn lockers on boats into fridges. What if we could actually convert the existing fridge using one of these kits?

Yet another round of research, measuring, poking around and head scratching ensued and we finally worked out that a Dometic Cold Machine CU55 compressor with a VD-07 ‘O’ shaped evaporator may well fit the bill. This combination has a 130-litre cooling capacity (the existing fridge being 112 litres) and the evaporator unit would fit inside the ‘freezer’ compartment. With power consumption at around 35 watts (approx 3 amps) with the compressor running, the solar panel should be able to keep the battery charged.

This kit was not ‘cheap’ however, coming in at around £500. But, a compressor fridge with a similar capacity to the existing unit would be twice that amount and wouldn’t fit!

The next conundrum was whether we were actually prepared to start hacking around a perfectly repairable fridge! A hole would have to be cut in the freezer compartment to get pipework from the evaporator unit to the compressor. Something well within my capabilities but still not a thing to be taken on lightly!

So, after an uncharacteristic “it’s got to be worth a go” from my good lady wife, an order was placed. This was actually easier said than done as no-one in the UK appeared to have any stock! Eventually, we sourced one from Seamark Nunn and although it wasn’t actually in stock, the lead time was acceptable. Alongside the main ‘kit’ we also ordered an auto-switching mains power supply (if there is 240v available, it uses that, otherwise it uses the leisure battery power). If I was to be pulling half the caravan apart, I may as well cover all scenarios.

That covers the ‘why and what’ of our fridge upgrade. In Part 2, I’ll cover the installation, teething problems and eventual solutions.

Abbey Vogue 460 - 2007
Our 2007 Abbey Vogue 460
Solar charger and battery monitor
Solar charger and battery monitor
Thetford Fridge
Thetford 3-Way Fridge
Dometic CU55 Cold Machine with VD-07 Evaporator
Dometic CU55 Cold Machine with VD-07 Evaporator

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