Fridge Fan Temperature Control Relay Switch

[steveh57]

I've set up the item below to drive a couple of PC fans in the fridge top vent, just trying to set up the temperature settings. I believe other funsters may use something similar, I'm just wondering what sort of figure for the dead zone people have set. Currently set at 5 degrees , so the temperature has to rise by 5 degrees from the set coolant temp before the fans are activated and then of course switch off when the desired coolant temperature is reached
Picture courtesy of Ebay

 

[Two on Tour]

I have ours set at 2.5c to keep our condenser temperature in it's sweet spot.

 

[steveh57]

Thanks, Just a matter then of finding my set up's sweet spot

 

[Two on Tour]

Our temperature sensor is wedged in the cooling fins of our condenser almost touching the condenser pipework and as a guide for you I have the fans come on at 40.5c and cool down to 38c to switch them off, but of course it's likely this will be different for your fridge/freezer.

 

[steveh57]

As you say it's different for every setup, my temperature sensor at present is to the left of the fans behind the top vent

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[Lenny HB]

I always set mine for a 2° hysteresis and for the fans to come on when the ambient is 25° actual temperture setting depends on where you mount the thermistor.

 

[Richard n Ann]

The dead zone is known as the differential or hysteresis on some controllers

Our sensor is in the fins on the left had side (coolest side) it was set to 41c but sometimes it was coming on at night so I've changed the setting to 48c.

Things to note:
If you take the top louvres out the fan runs much less and not at all at night.
Also if the sensor is pushed into a tube (or anything that insulates it) the differential will naturally be bigger.
Don't run the fans too much, the absorption system uses heat to drive the cycle.

 

[Two on Tour]

Our sensor is in the fins on the left had side (coolest side) it was set to 41c but sometimes it was coming on at night so I've changed the setting to 48c.

I used my infared thermometer to find where the temperature transition point was along the length of our condenser, and ours was towards 2/3rd's along the condenser, and I placed the sensor a little to the hot side of that.

 

[Richard n Ann]

I used my infared thermometer to find where the temperature transition point was along the length of our condenser, and ours was towards 2/3rd's along the condenser, and I placed the sensor a little to the hot side of that.

Is that where the vapour ends and liquid starts?

 

[Two on Tour]

Is that where the vapour ends and liquid starts?

Yup, that's my understanding.

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[Richard n Ann]

I suppose as long as the liquid line is full but I keep applying my experience of compressor systems so who knows where the sweet spot is

On a compressor fridge the liquid line is slightly warm normally unless it's loaded up with warm beer etc, then it may get quite warm

How warm is your liquid line as you have it set up?

 

[Two on Tour]

I have tried various positions for our sensor and I find that with the sensor in close proximity to the condenser pipework just prior to the condensing point, gives me the the most constant and reliable operation of our fridge/freezer.
With the sensor in the top vent airflow, I found the fridge/freezer temperatures fluctuated too much due to things like ambient air temperature changes, additional heat from the sun playing on the bodywork area of the fridge/freezer and wind direction. The sweet point of the condensing point and temperature of the condensing point are pretty well a constant, so that to me would be the most obvious point to take a temperature reading.

 

[Richard n Ann]

Mine's just switched off at 34c

 

[Two on Tour]

I suppose as long as the liquid line is full but I keep applying my experience of compressor systems so who knows where the sweet spot is

On a compressor fridge the liquid line is slightly warm normally unless it's loaded up with warm beer etc, then it may get quite warm

How warm is your liquid line as you have it set up?

As I said, I used my infared thermometer to find where the temperature transition point i.e. where the temperature dropped away and then I adjusted temperature of the fans cutting in and cutting out until I got the best results of the fridge/freezer lowest temperatures and being stable. This for out setup is 40.5c

 

[Lenny HB]

I have tried various positions for our sensor and I find that with the sensor in close proximity to the condenser pipework just prior to the condensing point, gives me the the most constant and reliable operation of our fridge/freezer.
With the sensor in the top vent airflow, I found the fridge/freezer temperatures fluctuated too much due to things like ambient air temperature changes, additional heat from the sun playing on the bodywork area of the fridge/freezer and wind direction. The sweet point of the condensing point and temperature of the condensing point are pretty well a constant, so that to me would be the most obvious point to take a temperature reading.

On the last 2 vans I've mounted my centrally above the fans but I have mounted it on an aluminium strip so that it doesn't respond to short fluctuations.

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[Two on Tour]

Last week I removed our bread and egg store, which was for the most part, was our redundant microwave as we are virtually off grid all the time.
I knew that there was a 30mm gap between the fridge/freezer sides and the housing around it as it has been a useful space to run cables to keep them hidden.
I also found that there was a 75mm gap above the fridge/freezer.
I made up layers of foil sided bubble wrap and placed these down the gap on either side of the fridge/freezer and placed 75mm of blue styrofoam on the top and this has given my at least a 2-3 degree drop in the fridge/freezer temperature.

 

[Lenny HB]

Last week I removed our bread and egg store, which was for the most part, was our redundant microwave as we are virtually off grid all the time.
I knew that there was a 30mm gap between the fridge/freezer sides and the housing around it as it has been a useful space to run cables to keep them hidden.
I also found that there was a 75mm gap above the fridge/freezer.
I made up layers of foil sided bubble wrap and placed these down the gap on either side of the fridge/freezer and placed 75mm of blue styrofoam on the top and this has given my at least a 2-3 degree drop in the fridge/freezer temperature.

Can't do that on mine it's a running fit & oven on top of the freezer.

 

[steveh57]

Mine was a slightly tedious install as I have a coated gas pipe running straight across the top grille vent, I had hoped to attach the fans to the grille but no room at all, so they've gone just behind the gas pipe. The sensor is attached to the left of these on the gas pipe at present and it's reading around ambient but I take on board the previous comments. We'll see how it goes, at least I now have some clues for fine tuning. Thanks everyone.

 

[Stewart J]

After much trial and error mine is set to cut in at 39 deg C and out at 34.6, once it cuts out temp continues to drop to 1.5 - 2 degrees. it’s a very hot day presently (26.5) and have full sun on fridge vents, freezer has never been very good since new despite dealer trying to sort it -4/5 on a really good day without the fans it’s a joke.

 

[Richard n Ann]

This is the bit we're interested in:

Labelled up with the terms above

So looking at it the heat that drives the system is below the heat exchanger and by the time the vapour refrigerant gets to the heat exchanger the heat has done it's job (separating the refrigerant from the liquid). My thinking then is that the liquid pipe which exits the heat exchanger on the left can be at ambient temperature or maybe just above.

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[Lenny HB]

After much trial and error mine is set to cut in at 39 deg C and out at 34.6

The actual set temperature is a bit meaningless and a case of experimenting as it depends on the installation and the position of the sensor. I always try to aim for the fans switching on when the ambient temperature gets to 25 deg.

 

[gus-lopez]

Mine , at present ,cuts in at 38ºc with an 8º differential. As the ambient temp is 34ºc at present they rarely go off. it usually runs at least 20 hour/day at present.
Until recently it was set with a cut in of 33º but i thought i would try a higher temp.
If I remember correctly the absorption fridge ammonia temp when a cooled liquid is usually pressurised so that it is 35ºc ? So in reality when in a high ambient place like where I live the fans really need to run permanently.