I'm not sure what it is but I think I have a problem with my fridge. For the last 2 years it's been trouble free and whisper quiet, turning on for 8-9 mins every 70-75mins, but in the last week or so its coming on for about the same 8-9mins, but on average after 38 or so minutes and now it sounds like a Mack truck at idle! Nothing is changed in the way I use the fridge or stack it, so I'm wondering what's going on. It's a Danfoss compressor with a vertical cold plate(?) inside the icebox.
I would appreciate any opinions or help to diagnose what the problem is and what I would need to do next. Thanks.

If it is an air cooled unit with a fan pulling air through the condenser, my first thought is that a blade is hitting something,
More like a tinkling sound that a Mack truck though.

gary

Thanks Gary. Yes it is an air-cooled unit but it has a plastic fan blade. I just had a look, but it doesn't look or sound like it's hitting anything - although the condenser coil seems to be vibrating more than it used to, so perhaps it's the fan unit?, but I don't really know what to look for.

Bit of a concern that it's starting more often is it still getting as cold as it was ? I had one that started out like that then ran more and more often till it ran the battery down, turned out to be a gas leak

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woko said..
Bit of a concern that it's starting more often is it still getting as cold as it was ? I had one that started out like that then ran more and more often till it ran the battery down, turned out to be a gas leak

I bought a 18 litre fridge/freezer online three months ago for $289.
It freezes to minus twenty (ice cubes if you want).
It is portable but I keep it on the boat.
I have a built in fridge but suspect my new one uses far less electricity.
I am happy with my new system.

Some hermetically sealed compressor units have small springs which centralize and absorb vibration between the compressor and outer housing. If one of these springs breaks or comes adrift, the internal compressor can knock on the external housing.
You can sometimes diagnose it by slightly tilting the comp/condenser unit at different angles whilst its running, the noise will get louder or may go away. Often if one of these springs is broken, there is a large knock at start up .
Also check that the evaporator plate is free of ice. If it ices up you may not be getting heat exchange from the fridge box , causing excessive running and may even return liquid refrigerant back to the compressor. That's not good and the compressor wont like it.


You can also get an idea of the systems operation by feeling how hot the discharge line at the compressor is. It should be warm to hot to touch.
Feel the line that exits the condenser containing liquid refrigerant, it should be slightly above ambient temperature.
Feel the suction line returning to the compressor. It should be cold but with no Ice or excessive sweating.

Get a look at the evaporator plate and see if it is covered with frost or half covered or just a tiny bit. Half or a tiny bit may detect low gas
If its a huge block of ice,, defrost it and check for poor sealing on the lid or door.

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woko said..
Bit of a concern that it's starting more often is it still getting as cold as it was ? I had one that started out like that then ran more and more often till it ran the battery down, turned out to be a gas leak

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Jolene said..
Some hermetically sealed compressor units have small springs which centralize and absorb vibration between the compressor and outer housing. If one of these springs breaks or comes adrift, the internal compressor can knock on the external housing.
You can sometimes diagnose it by slightly tilting the comp/condenser unit at different angles whilst its running, the noise will get louder or may go away. Often if one of these springs is broken, there is a large knock at start up .
Also check that the evaporator plate is free of ice. If it ices up you may not be getting heat exchange from the fridge box , causing excessive running and may even return liquid refrigerant back to the compressor. That's not good and the compressor wont like it.


You can also get an idea of the systems operation by feeling how hot the discharge line at the compressor is. It should be warm to hot to touch.
Feel the line that exits the condenser containing liquid refrigerant, it should be slightly above ambient temperature.
Feel the suction line returning to the compressor. It should be cold but with no Ice or excessive sweating.

Get a look at the evaporator plate and see if it is covered with frost or half covered or just a tiny bit. Half or a tiny bit may detect low gas
If its a huge block of ice,, defrost it and check for poor sealing on the lid or door.

Thanks Woko and Jolene - this seems to correlate what's going on.

Woko - its starting up more often, but the temp is still ok.

Jolene - the compressor is still solidly mounted, and there is no knock on startup, but when I jiggle the coil (mounted separately beside the compressor) the noise is reduced, but still not as quiet as it used to be.
Both lines are as they should be, 1 cold, and 1 slightly warm - but yes, there is about 1-2mm of ice on about the bottom half of the plate. The lid seals well and I have an insulating mat over the lid as well.
It also seems to make a sighing noise when it turns off - is this the gas settling back into the system? Im starting to think it's a low gas problem. How do I fix that?

Defrost that plate, get all the ice off it and test run it again.
Look for evidence of leaking gas, Oil is carried throughout the system by the gas, If gas has leaked somewhere, the oil will show some staining and even attract dirt.
Check whether the fridge box has a chemical smell,,, leaking gas/oil has a unique smell or odour. often you become accustomed to it and don't realise what it is,
Paint some soapy water on all the joints of the system and look for tiny bubbles.,,, small leaks make small bubbles slowly, this can take time.
That hiss you can hear can relate a system that may be low on gas but it could also be something like a malfunctioning TX valve or capillary orifice that is starving the gas from the evaporator.
If defrosting doesn't fix it and you cant find a leak, you may need a fridge guy with some gauges to diagnose what is going on.
Either way you may need a Fridgey to add gas or replace components in the system.

Thank you so much for the information.
I'll start troubleshooting from your list this afternoon - it only takes a couple of hrs to defrost.

Original posted symptoms.
1/ ,turning on for 8-9 mins every 70-75mins, but in the last week or so its coming on for about the same 8-9mins, but on average after 38 or sominutes
2/ sounds like a Mack truckat idle
3/ It also seems to make a sighing noise when it turns off - is this the gas settling back into the system
4/ starting to think it's a low gas problem

1/ No refrigeration system will run for 8-9 mins every 70-75mins. So I suggest it has been running longer than that, more like 8-9mins,every 38 or so minutes. It was running so well and quietly that you didn't notice.

2/ Ga-,chunk, ga-chunk, ga-chunk? That is my idea of a Mack idling. Any chance of recording and posting the noise?
Noises and rattles usually come from something that has moved or rattled loose.
Except when a sleeping cat is caught in the system when it starts up. Do you ave or did you have a cat?
Jolene suggested that the compressor internals might have come of the supporting spring mounts.
This does happen but is extremely rare.
It takes a lot for this to happen, such as the compressor being violently shaken or transported upside down.
Have had a capsize or rollover recently?

My guess is that the new noise has convinced you that it is cycling more often than before and I think that if you can find the rattle. defrost the unit and start from scratch you will be fine. At least I hope so.
Condenser coil and casing are often bolted to base and bolts come loose. Sometimes tack welded and weld breacks.
Condenser fan bracket can come loose.
Electrical box can come loose and rattle against the compressor or something else.
A spoon. fork (or cat ) could have fallen in behind the unit.

3/ The compressor has a high pressure discharge side (warm or hot) and a low pressure suction side (cool or cold). If the compressor stops without equalizing it will start against the high pressure in the discharge side. Not a problem with powerful units but in smaller unit especially 12 volts it will mean a high amp draw on start up.The sighing that you are hearing is the equalization of the system to make for an easy (low amp) start up and is perfectly normal.

4/ A low gas problem means a leak. This is your worse case.
If there is a leak it will not be partial as it will eventually leak all of the gas. . The unit will run almost continuously.
The compressor will get very hot as there is no cooling gas returning to cool it internally and you will have no frost on your plate..
Some systems have all brazed tubing and some have tubes that are connected with brass flair nuts.
Usually with a refrigerant leak there is also so oil leaking (not always) If you have flair nuts , check for oil.
If the tubes are brazed that will leak where they have rubbed against something . Again check for oil.

All the best

Gary

Thanks Gary! I just read your post and you made me laugh at least twice! haha - no cats, and no capsizes since I last sailed a cat. It was a good way to start the day - with a coffee and a laugh Thankyou.
. Jolene - I used your checklist after a thorough defrosting, and went through the whole lot - no smell,no oil, no dirt, no leaks, no bubbles, i used a mirror to check behind where I couldn't see. On initial startup the cold line frosted over briefly but it soon evaporated and was barely sweating. Then I noticed the noise again. Most of the joints are brazed but these 2 are flared nuts. After working out just where the noise was coming from I came up with a super duper high-tech solution:


(The blob of silicone was already there, so vibration has been an issue before I'd guess)

So, with the sanding block in place, it cuts in and runs as quiet or quieter than before!
Thank you Gary for all the extra details - between you and Jolene I now I know my system a whole lot better - always a plus. In regard to run times there's some screenshots from last night while I was monitoring with a stopwatch on my mbl. Pretty consistent running of around 9min30s, but the intervals between were getting longer and longer - settling at around about 58 minutes by the time I managed to get to sleep. Original figs quoted were from last winter, so I hope it'll get back close to that again.
Thanks to you both - i learnt alot.