12volt LEC refrigerator.

[Karen Lea Rainey]

My fridge wont work at all below around 3c, it began working again as soon as the weather warmed up.

I've got used to it now and stopped worrying, but the ice box doesnt work in winter.

It's an old fashioned ' Engel ' fridge by the way.

[Nightwatch]

7 minutes ago, Karen Lea Rainey said:

My fridge wont work at all below around 3c, it began working again as soon as the weather warmed up.

I've got used to it now and stopped worrying, but the ice box doesnt work in winter.

It's an old fashioned ' Engel ' fridge by the way.

It seems this is what has happened with ours.

[cheesegas]

Most fridges have the same compressor, a Danfoss BD35 or BD50. If it's really old it'll have a single speed BD2 or 3...but depending on the design it'll run a lot or not much; some have a fan cooled heat exchanger, some use the side. I have a fan cooled Engel with a BD25 which is getting on for 30 years old and still works perfectly. The compressor rarely fails, the control box goes wrong first and it can't be bypassed.

 

The thermostat on most fridges is on the evaporator plate that forms the freezer box, it doesn't measure the temperature of the air in the fridge, only the freezer compartment. If that never heats up enough to trigger the thermostat, the fridge stays off.

[MtB]

7 minutes ago, cheesegas said:

The thermostat on most fridges is on the evaporator plate that forms the freezer box, it doesn't measure the temperature of the air in the fridge, only the freezer compartment. If that never heats up enough to trigger the thermostat, the fridge stays off.

 

That's interesting. I thought it was the other way around. 

 

On mine, the thermostat capillary tube disappears into about an 8mm diameter plastic tube buried in the foam insulation. When I pulled to old stat out, it went in to a depth of about 18". The new one went back in the same amount. 

 

The oddest thing is, there is no bulb on the end of the capillary, so I suspect the whole length of the capillary is doing the sensing.

 

 

[cuthound]

6 hours ago, Loddon said:

Fridges and freezers have a specific temperature range that they will work in.

Many fridges/freezers won't work properly under 10deg so don't work in garages etc. I had to get one that specifically works down to 0deg as I wanted to place it in the garage.

 

Indeed, fridges work by compressing gas into a liquid and then allowing the liquid to evaporate, which causes the cooling effect. If the ambient temperature is too low the gas won't evaporate and the fridge won't work. Different refrigerants evaporate at different temperatures.

 

See if it works as the temperature in the boat rises.

Edited January 22, 2023 by cuthound
Spillung

[Francis Herne]

Definitely worth shorting out the thermostat and see if that helps. I had different symptoms when mine failed (intermittent operation with a lot of short cycles) but it's quite possible for it to fail open.

 

On 22/01/2023 at 11:46, MtB said:

Stat failure is particularly probable on a converted 230V to 12v fridge as they rarely fit a relay to carry the far higher current a 12v compressor draws. They just leave the 230Vac one in place as it will work for a while, but it is switching a far higher than design current, leading to early failure.

All the 12V fridge conversions I've seen so far have been based on the Danfoss BD35 compressor (or licensed copies thereof). That has a brushless motor driven by an electronic controller; the thermostat is only used as a digital input and carries next to no current. Are you thinking of any particular type/brand with the motor switched directly? Low-voltage DC rather than high-voltage AC is quite different for switching in any case.

Edited February 5, 2023 by Francis Herne

[Tracy D'arth]

14 hours ago, Francis Herne said:

Definitely worth shorting out the thermostat and see if that helps. I had different symptoms when mine failed (intermittent operation with a lot of short cycles) but it's quite possible for it to fail open.

 

All the 12V fridge conversions I've seen so far have been based on the Danfoss BD35 compressor (or licensed copies thereof). That has a brushless motor driven by an electronic controller; the thermostat is only used as a digital input and carries next to no current. Are you thinking of any particular type/brand with the motor switched directly? Low-voltage DC rather than high-voltage AC is quite different for switching in any case.

Probably they fail because there is only a very small current and the contacts oxidise a bit. Well worth exercising them on and off for a few minutes.

[Nightwatch]

As mentioned before. Fridge now working as per normal. It seems it was the very low temperature within the boat that convinced the fridge to have a few days ‘off’.