Cold fridges, however compressor runs almost constantly

BigJoe

BigJoe

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We have 2 12 volt Vitrifrigo fridges each with Danfoss BD35F compressors.

The fridges are cold enough, however, the problem is they run almost constantly. The boat is 10 years old, and the fridges have run pretty much nonstop from new.

I have 2 lines of thought…………………
1. they possibly need gassing.
2. a thermostat problem.

Any thoughts or advice would be great.
 
or there is an airleak into the fridge. That is a common issue with home fridges in that an airleak around the seal means the compressor is always fighting against a temp rise.
 
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I have a front opening and a top opening well type.

The top opener is the worst, even with then thermostat turned right down, it only switches off for one or 2 minutes, then comes back on.

The front opener, is similar, but waits of for 10 to 15 minutes before kicking on.
 
Joe: you raise the possibility of the fridges being improperly gassed, although it sounds a little unlikely that two would have the same problem. This page has useful info for diagnosing that, by the estimable Vyv Cox:
https://coxengineering.sharepoint.com/Pages/Refrigeration.aspx

If the pump runs constantly and yet doesn't make the fridge(s) excessively cold, it seems doubtful the thermostat is at fault - and two thermostats even less so. It may be a matter of inadequate insulation or poor air circulation around the cooling elements. As a (very flexible) rule of thumb, the compressor shouldn't be running much more than half the time. Yours must be guzzling power.

A cheap and simple mod to help air circulation is to fit a computer fan (say 75mm) to blow over the cooler. They draw very little power, and with many control units can easily be wired to come on only when the compressor is running. It can make a significant and worthwhile difference, but your problem looks too pronounced for it to be a complete fix.

You describe the problem as "from new": how long is that? And from your signature, can we conclude that the boat is new to a hot climate? If it was in cooler conditions before, did it behave any differently?

Incidentally, an infra-red thermometer is a handy way to monitor this (and many other) on-board items:
https://www.amazon.co.uk/Benetech-N...83345;)&sr=8-2&keywords=infra-red+thermometer
Handy for jam-making, too ;)
(The same thing is probably available a little cheaper elsewhere on Amazon.)

P.S. Apart from measuring internal fridge temperatures, this will allow you to assess the effectiveness of the insulation. A difference of more than a couple of degrees between the fridge's external temperature and the ambient temperature of nearby surfaces inside the boat suggests inadequate insulation. The current figure for our well-insulated fridge (on a not particularly hot day, just 27ºC inside the boat) is less then 0.5ºC.
 
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If you think the fridge might be short of gas you might be able to judge this with an infrared thermometer with laser pointer.

The evaporator inside the fridge normally consists of a tube zigzagging across the evaporator panel. One end will come from the capillary tube the other goes to the compressor inlet. If the evaporator is set vertically the liquid refrigerant will normally enter at the bottom and rise to the top and out to the compressor.

If you find the cold pipe to the compressor measure its temperature with the compressor running, then using the pointer find out which end of the evaporator is about the same temperature. Then follow the grid until you observe a distinct drop in temperature, this is the point where the refrigerant has completed its boiling and has absorbed most of the heat it is going to, so its temp will then rise as it passes through the rest of the evaporator grid and then along the suction pipe to the compressor.

I would expect the point of temperature drop to be within 1 or 2 passes of the outlet from the evaporator. If you find this point further back then the thing could be notably short of gas.

This being the case you need to find out where it has gone. Fridges are rarely porous even on a molecular level. Signs of leakage are oily patches, and if it has a removable flare cap, or worse still a line tap valve, these are a common leak point. If you don't seal the leak and just recharge you are merely putting off the failure to another day, and BTW adding gas to a leaking system is illegal, although there is not much in the way of enforcement, but it is hardly environmentally friendly either.
 
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Similar happened to me recently. The end of the thermocouple had become detached from the cooling plate. Once reattached fridge started cycling as usual. Sorry but not sure if the terminology is right :rolleyes:
Donald
 
MacD,

Thanks to the link to Cox engineering, it’s very helpful.

We have had the boat in Spain for 10 years, but we have only recently moved aboard full time, before that we used her most weakens, so we never really switched off the fridges, in that time.

Both fridges are both relatively cold, even when turned down to the lowest setting, but when I increase the thermostat control, they run continually.

I have thought about additional cooling but that’s possibly a winter job.

Super,
thanks for your input, it’s very helpful
 
BigJoe said:
Both fridges are both relatively cold, even when turned down to the lowest setting, but when I increase the thermostat control, they run continually.
thanks for your input, it’s very helpful
Click to expand...

You're very welcome, Joe.

If there isn't a specific problem, it could simply be that your system isn't powerful enough to bring the fridge down to the lowest temperature your thermostat can be set for. (Due to smallish compressor, inadequate evaporator plate, inefficient cooling or inadequate insulation.) The pump keeps trying, but it's impossible.

That said, the thermocouple should be sensing evaporator plate temperature, as opposed to the general temperature inside the fridge, so you'd expect it to cycle on and off to some degree. Worth checking for what Aja experienced.

But of course it could be something else...
.
 
Hello I am glad you found my article helpful on my Dads website. I work with marine and leisure fridges all the time now based in north wales and the south coast. I workeed out in mallorca for 10 years mostly in marine refrigeration and air conditioning. I have a couple of questions to help determine the faults you explain. It does sound like there isnt a problem with the refrigerant because if it had leaked down to a level where it affected running it would have kept leaking and would not have lasted 10 years without all the refrigerant leaking out. I would suggest that as said above you will either have problems with a lack of insulation or a lack of cooling to the condenser on the compressor end of the fridge. Have you got good clear ventilation paths that circulate fresh air from the cabins to the condenser? the insulation in a cabinet is recommended to be at least 100mm. is that what you have? presumably the vertical door cabinet is a factory made one? if so it will have less than the minimum insulation but you should still have 50% running at worst really once the cabinet is cold. Are you getting any ice build up on the evaporator? if so this can be insulating the plate and stopping it from cooling the cabinet. the plate usually runs at -11C if insulated with ice it will only be 0C. It is a common fault that people turn the thermostat lower and lower until it ices up and doesn't cool properly. If you continue to have issues with continual running and possibly freezing things in the fridge it is probably a faulty thermostat ( they often lose the gas charge in the capillary tube of the thermostat and so lose the ability to switch off.) make sure the capillary tube is firmly connected to the evaporator plate too as this can also cause issues of not switching off. let me know the answer to these questions and I can see what else I can do to help.
 
owen-cox said:
Hello I am glad you found my article helpful on my Dads website. I work with marine and leisure fridges all the time now based in north wales and the south coast. I workeed out in mallorca for 10 years mostly in marine refrigeration and air conditioning. I have a couple of questions to help determine the faults you explain. It does sound like there isnt a problem with the refrigerant because if it had leaked down to a level where it affected running it would have kept leaking and would not have lasted 10 years without all the refrigerant leaking out. I would suggest that as said above you will either have problems with a lack of insulation or a lack of cooling to the condenser on the compressor end of the fridge. Have you got good clear ventilation paths that circulate fresh air from the cabins to the condenser? the insulation in a cabinet is recommended to be at least 100mm. is that what you have? presumably the vertical door cabinet is a factory made one? if so it will have less than the minimum insulation but you should still have 50% running at worst really once the cabinet is cold. Are you getting any ice build up on the evaporator? if so this can be insulating the plate and stopping it from cooling the cabinet. the plate usually runs at -11C if insulated with ice it will only be 0C. It is a common fault that people turn the thermostat lower and lower until it ices up and doesn't cool properly. If you continue to have issues with continual running and possibly freezing things in the fridge it is probably a faulty thermostat ( they often lose the gas charge in the capillary tube of the thermostat and so lose the ability to switch off.) make sure the capillary tube is firmly connected to the evaporator plate too as this can also cause issues of not switching off. let me know the answer to these questions and I can see what else I can do to help.
Click to expand...

Hi there, I am having an interesting problem with my Vitrifrigo top loader fridge. The thermostat was replaced 4 months ago and because one can’t access the outside without breaking open the cabinet the sensor probe was fastened to the inside of the unit, where it ices up, and not directly on the evaporator. This initially worked fine but now the thermostat won’t switch the compressor off and the fridge keeps running. I swopped the thermostat around with my upright fridge to rule it out as faulty and no luck, top loader still runs constantly (and the upright switches off and on as expected). So if it’s not the thermostat then any ideas on what the problem could be?
Regas was also done 4 months ago and new door seal.
 
Is the stat sensor near the top of the fridge box ?

But why was a re-gas done ?

Was the (I presume) leak requiring this resolved, if not possibly back to where you were previously. If you simply find a need to re-gas again and do not remove the root cause you will keep needing to re-gas, except now you know you have a leak as there is no other reason to keep needing to re-gas, and to simply re-gas again would actually be illegal, akin to fly tipping IMHO. Decent folk do not fly tip, so same folk should not re-gas leaking fridge systems.
 
Can I ask have you measured the fridge temperature at all? Was the original thermostat fitted to the evap plate, if not a faulty thermostat sounds like gas loss again
 
macd said:
This page has useful info for diagnosing that, by the estimable Vyv Cox: https://coxengineering.sharepoint.com/Pages/Refrigeration.aspx
Click to expand...

I'd like to read that but when I follow the link it prompts me to log in with a Microsoft account, and when I log in with my personal account I get an error along the lines that I am not listed as a user in the Coxengineering SharePoint account. Anyone else have an issue accessing that document, or have a copy they could please forward?

Thanks

Anthony
 
Anthony said:
I'd like to read that but when I follow the link it prompts me to log in with a Microsoft account, and when I log in with my personal account I get an error along the lines that I am not listed as a user in the Coxengineering SharePoint account. Anyone else have an issue accessing that document, or have a copy they could please forward?
Click to expand...

Yep, same problem.
 
I think I may be a numpty. When I rebuilt our box fridge I followed info about position and insulation etc. But I just took the end of the long, flexible, thermostat thing and layed it across one edge of the floor of the fridge. Is supposed to touch the fridge element (evaporator?)?
Because it does cycle quite quickly on and off.

Right, where's the D hat ?
 
mattonthesea said:
I think I may be a numpty. When I rebuilt our box fridge I followed info about position and insulation etc. But I just took the end of the long, flexible, thermostat thing and layed it across one edge of the floor of the fridge. Is supposed to touch the fridge element (evaporator?)?
Because it does cycle quite quickly on and off.

Right, where's the D hat ?
Click to expand...
It’s up to you. I have had the thermostat set to 5 degrees and at the warmest part of the fridge well away from the plate and at -10 degrees right on the plate when I wanted nearby things to freeze.
 
Roberto said:
It's available on Vyv/Owen web site
Recharging marine refrigeration systems
Click to expand...
The guidelines referred to do say they do not comply with current Laws, and in my view do encourage illegal and unsatisfactory practices.

The Law concerning venting of refrigerants has been around for many many years (pre 2000), and in my view these instructions should be re-written to reflect both the current laws and good refrigeration practice.

It remains illegal for any firm to sell and any non registered firm or person to purchase refrigerants. There is a loophole that allows Halfords to sell pre-oiled refrigerant for automotive systems, but this loophole does not include its use within stationary systems, which as I understand the definition includes those system installed inside a boat.
 
When I had a similar sort of problem a fridge engineer suggested unplugging it for a day or two to let everything in the fridge mechanism defrost and for the refrigerant to percolate back to the reservoir. (obviously you have to store the food elsewhere in the meantime). It worked and the refrigerator was its old working self again.

We got the same advice when we moved house and when we bought a new unit. Just let it stand overnight before you plug it in

Clearly, if there's a leak it won't work, but if no leak is evident its worth a try. I have to declare I'm not a fridge engineer and I don't have an explanation and it may all be old wives tales...so thats my caveat.
 
That’s the way to often clear an ice blockage at the evaporator plate which restricts the gas flow, this can return quickly or stay ok for years.
 
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