PaulRainbow
Well-Known Member
Now that is showing your age!
lol, no not that accumulator. I was thinking air-con accumulator for some reason.
Fridge Thermostat
- Thread starter Norman_E
- Start date
lol, no not that accumulator. I was thinking air-con accumulator for some reason.
Norman_E
Well-Known Member
I presume you call it an accumulator, its a big stainless steel box.
coopec
N/A
William
Maybe replacement of the thermostat is simpler than you believe?
It is a long time ago but when I contacted a fridge mechanic to get him to replace a faulty thermostat he was decidedly reluctant. He asked me why I didn't do it myself. When I told him I didn't know how he asked me to get a particular generic thermostat and he would show me.
When he arrived he undid the cover off the adjustment dial, pulled the faulty thermostat out of a capillary type tube, threaded the new one in, attached the contacts and he was gone inside ten minutes.
Of course your fridge may be an entirely different design but I bet they make it easy to replace the thermostat.
Clive
Maybe replacement of the thermostat is simpler than you believe?
It is a long time ago but when I contacted a fridge mechanic to get him to replace a faulty thermostat he was decidedly reluctant. He asked me why I didn't do it myself. When I told him I didn't know how he asked me to get a particular generic thermostat and he would show me.
When he arrived he undid the cover off the adjustment dial, pulled the faulty thermostat out of a capillary type tube, threaded the new one in, attached the contacts and he was gone inside ten minutes.
Of course your fridge may be an entirely different design but I bet they make it easy to replace the thermostat.
Clive
pvb
Well-Known Member
That sounds like an accumulator, and it wouldn't be unusual for the compressor to switch off for hours. Is this changed behaviour of the fridge? Is the boat new to you?
macd
Well-Known Member
I'm absolutely no authority on marine fridges, Norman. But from the way it works, I doubt an accumulator/holding plate can use a thermostat in the way you imagine. Equally, they cannot readily maintain a consistent temperature (unless, perhaps, clad with an unfeasable amount of insulation).
Suggest you read this page: http://www.penguinfrigo.co.uk/shop/product/585/
And particularly, given the issue you mentioned in your opening post, this sentence: "Fridges fitted with holding plates are subject to greater temperature variation (usually around 10°C)"
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Norman_E
Well-Known Member
I have had the boat 10 years. The original compressor failed and was replaced, almost immediately followed by failure of the CLD automatic inverter that drove it. Since then it has taken far longer to cycle on and off. The new compressor takes longer to cool it down from first starting, then cycles off for longer, allowing the fridge to warm more than it did. There is an evaporator valve below the stainless accumulator box and that was also changed, and in doing it I'm pretty sure that the engineer moved the end of the thermostat. Changing the latter would be a nightmare job as the point where it enters the fridge is absolutely inaccessible from the outside.
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Gumpy
Well-Known Member
When the thermostat on our boat fridge packed up, wouldn't switch off, we fitted similar to this,
http://www.ebay.co.uk/itm/131101201417
Left the old stat in situ but set on coldest it can be and controlled the supply to the fridge using the external stat. Temp sensor was fed in through the condensate drain hole..
It worked so well at keeping the temp stable and reduce consumption (from origional consumption not when it was broke) that a friend modified his fridge to be the same.
http://www.ebay.co.uk/itm/131101201417
Left the old stat in situ but set on coldest it can be and controlled the supply to the fridge using the external stat. Temp sensor was fed in through the condensate drain hole..
It worked so well at keeping the temp stable and reduce consumption (from origional consumption not when it was broke) that a friend modified his fridge to be the same.
owen-cox
Well-Known Member
This is a common fault with old mechanical type thermostats. As they age they seem to get a wider differential(start and stop band) this would explain it. I recommend don't mess about with it just change it for a digital one. I got one on eBay for £3.49 it seems good and amazing value. Fit the probe on the plate as others have said then set it to about 0 degrees plate temperature which should maintain 5 degrees fridge temperature. You can adjust it up and down as you feel necessary afterwards. This will also give you a read out of the temperature so you can see it working.
I see you have eutectic holding plate in the fridge so this definitely needs to have the thermostat sensor fixed to the plate. The way they work is that they freeze the liquid in the plate to about 0 degrees. It takes a lot of running to go from liquid defrosted to fully frozen. Then once fully frozen any more running of the compressor is pointless. Check that it is not set below about -2 degrees or it will run and run without making any difference to the temperature. The fridge should stop and then use the holding ability or the eutectic plate to stay cold usually up to 12 hours ( if the insulation of the cabinet is good). Then the compressor will start again and run for a long time until frozen again. These are very good systems but the main drawback is that there is very little temperature control in the fridge itself. They are great for freezers but not so good for anything that needs a specific temperature unless that is between 5 and 2 degrees. I still think you will never get this system to work correctly without changing to a digital thermostat. I have changed hundreds of Nautor Swans over to digital as the older ones used mechanical ones that never worked well.
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Norman_E
Well-Known Member
Unfortunately the thermostat has to switch mains voltage so I can't use any of the 12 volt digital ones. There are similar 220 volt ones on sale so I will look into that idea.
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Norman_E
Well-Known Member
Thank you. I was told by a fridge engineer that the accumulator should be cooled to minus 14 degrees! I might need to experiment with settings. As far as I can tell there is no way of actually attaching the probe to the accumulator and ensuring it remains in contact.
owen-cox
Well-Known Member
This looks like an ideal thermostat for the duty.
john_q
Well-Known Member
Just been looking at Plate temperatures as my thermostat broke yesterday
I have a 12V DC Isotherm 4701 ASU Magnum water cooled fridge This unit uses a eutectic type stainless steel holding plate with an average holding temperature of minus 9ºC.
Plate Temperatures
The Isotherm ASU unit senses battery voltage, if it is high >13.2V then it will charge up the holding plate, when the battery voltage drops to <12.7 it goes into Economy Mode
High Battery Voltage charging, over 13.2V
Starts at –10°C (14°F)
Stops at –14°C (7°F).
Economy Mode <12.7V
Starts at -1°C (30°F)
Stops at -6° (21°F).
I have a 12V DC Isotherm 4701 ASU Magnum water cooled fridge This unit uses a eutectic type stainless steel holding plate with an average holding temperature of minus 9ºC.
Plate Temperatures
The Isotherm ASU unit senses battery voltage, if it is high >13.2V then it will charge up the holding plate, when the battery voltage drops to <12.7 it goes into Economy Mode
High Battery Voltage charging, over 13.2V
Starts at –10°C (14°F)
Stops at –14°C (7°F).
Economy Mode <12.7V
Starts at -1°C (30°F)
Stops at -6° (21°F).
PaulRainbow
Well-Known Member
Key the plate a little and Araldite will stick it.
No doubt that'll be the wrong material, in the wrong place, doing the wrong job at the wrong time. But, i've repaired many an evaporator plate where someone has defrosted it with a knife using Araldite.
pvb
Well-Known Member
Nowhere near cold enough! Accumulator holding plates usually run at -8 to -12 degrees.
owen-cox
Well-Known Member
The economy mode is the one to look at. It will keep the fridge at a sensible fridge temperature. Their plate is sized to a volume of cabinet with an assumed insulation so that is why it has lower temperatures than I stated. Swans have an oversize plate on average 10% of the cabinet volume and if you ran down to lower than -5 you would freeze everything. It also depends what liquid they have in the eutectic plate. I used to make my own up with water and glycol. Freezer I would make it freeze solid at -25. And fridges -5. Then add the liquid to the plate. I have built quite a few eutectic plates over the years and they worked fine at this temperatures.
owen-cox
Well-Known Member
I hadn't fully read the thread at the point I said that and thought it was a standard evaporator. So you are correct. They shouldn't need to run that cold if they are correctly sized. They may be wasting energy cooling after the liquid in the plate is frozen.
owen-cox
Well-Known Member
I'm sure araldite would be fine as you suggest. I used to buy roll bond plates for around £7 each from a factory in Italy so I didn't ever bother fixing them. I tried a few and some worked others didn't so to make sure I could guarantee them I would replace them.
pvb
Well-Known Member
Interesting, but you did say "I see you have eutectic holding plate in the fridge...".
owen-cox
Well-Known Member
i should have edited the post and changed the values as I added the second paragraph in an edit.
All I can say is that I had a chap working for me who built all the camper and Nicholson fridges that all had eutectic plates and he used the temperatures that I do and Iceberg Norcool who built all Nautor Swan fridges amongst many others such as the one I serviced for many years on Velsheda use -5 for fridge and -25 for freezer plate temps.