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Philvayro44@gmail.com’s recent post on Fridge fans and Aaron Calder’s reminder of his approach found here - How to: Fit thermostatically controlled fridge cooling fans made me think that perhaps my recent upgrade and the test it had on a recent 3 weeks in France and Belgium etc might be of interest.

I cannot lay claim to the design of this system as it was prototyped by a caravanning good pal of mine who was an electronics engineer earlier in his career. The basic layout comprises of a Temperature controlled switch, a temperature controlled CPU fan circuit board and two 80mm Computer fans. The Temperature controlled switch I bought here:
Werbung: https://www.ebay.co.uk/itm/125655299055?var=426682352363

The circuit board, I bought here:
Werbung: https://www.ebay.co.uk/itm/333575149306

and the fans (2 of them) purchased here:
Werbung: https://www.ebay.co.uk/itm/166211479982

The assembly of the components was as follows.

First, the temperature controlled switch was tied to the coolant pipe just before the finned section. The switch is configured to pass current when the temperature it ‘sees’ exceeds 40c. Different temperature versions are available, as are a version that switches *off* at the designated temperature. Somehow, the first one I had was one of these so the circuit only ran when the coolant temp was *below* 40c. Not helpful! I attached the sensor to the pipe using a small spring. The output of this is the input to the circuit board. The circuit board has it own separate temperature sensor that is a ‘wand’ that senses the temperature of the air passing up through the void behind the fridge. As this temperature increases the fan speed is also increased.

The circuit board has the ability to control up to 3 fans. With a careful addition of a little blob of solder to a part of the circuit, the fans are controlled at the same speed, the default being one fan is speed controlled, the remainder run at base speed.
To assemble the set up, I made a small prototype from ali to make sure that the mounting plate would fit behind the external vent plate. When making that, I left as much open to vent air as possible in case of any failure in the circuitry.

The 12v feed I managed to re-use the feed to the sink tap as we never use it. That made the electrical feed very straightforward.

I have used the set up for the three weeks we were in Europe and my observations are purely subjective. First and foremost, my feeling is that the fridge has worked much more effectively. The temp was maintained at optimum as shown on a small temperature gauge I keep in the fridge. The fridge control was set at 5.5/6. It worked so well that we were able to freeze ice blocks to use in a sandwich bag. During the period we were away, we had varying weather conditions, including 30+c towards the end of the trip. The fridge happily maintained its temperature.

On the down side (depending on your point of view) the fans can wind up their speed if they are working hard but this tends to be in relatively short bursts. The age old problem of fridges venting int the awning space might just be an issue, but I can’t comment on that. On the plus side, this is a fit and forget solution that simply looks after itself as the operation is totally automatic.

The temperature controlled switch:
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Prototype mounting plate
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Completed mounting plate - note extra space to permit passage of air in the event of failure
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Assembled components on mounting plate
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Electrical feed point
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Final assembly in place
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Hopefully my rather rambling description makes sense but If I have confused anyone, please to fire away with any questions....

It appears on our fridge fan doesn't have a thermal switch fitted apart from a on/off switch on the kitchen unit are these fans designed to run ok for long periods continuous until you decide to switch it off

I hate to offer a definitive answer but my 3 week experience in my most recent trip would suggest yes. With them being temperature controlled, they seemed not to run over night and would run at quite low speeds much of the time. Only when the temperature went right up did they really fire up and then, often for just short bursts What I like about this system is it is constantly monitoring the environment and reacting accordingly. My guess is that that gives a lower load than when externally controlled and turned on from a switch when thought needed. That is pure conjecture of course..

And I never switch it off, it doesn't have an external switch and is completely automatic.....

hth...

And a quick search turns up the spec. Probably the most helpful thing to look at:

https://akasa.co.uk/search.php?seed=AK-FN076

seems to be rated up to 3000rpm and has a life of 40,000 hours