Why does ambient temperature stop a fridge or freezer?

[ericmark]

I can see how too high stops it working but not too low. Well in a way as soon as one reaches the point where it needs heating to maintain correct temperature well yes but if a freezer is set to -18°C and the ambient temperature is -15°C then one would think the freezer would have rather an easy time and there would be no problem.

However my freezer states minimum ambient temperature 15°C not really a problem but question is why should one freezer work at -15°C and another can't go below 15°C?

Is it something to do with the inverter control? I can see if the motor runs 24/7 and never switches off that it may not be able to run slow enough but my motor clearly does switch off.

In the past once a fridge/freezer motor started to run it would continue for an hour or more before it switched off the temperature of the unit was controlled by the mark/space ratio of motor running and static.

However the new inverter controlled unit will often kick in for just 45 seconds and I wonder why.

The unit seems to work well but would just like to get my head around this new technology and why an ambient temperature of 4°C to 15°C is a problem. OK below 4°C I understand it would need heaters to maintain the correct temperature but above 4°C what is the problem and why is it not a problem with some units?

 

[Burnerman]

As I see things, the ambient temperature of the air surrounding the condenser coils needs to be in the region of 10deg cooler than the refrigerant in the coils so that heat from the food can be lost into the air.
If that air is also very cold, then this heat loss can't take place well.
Thermostats within the appliance also tell the compressor that things are cold enough anyway.
To remedy this, I guess one way would be to switch the compressor on at timed intervals, bypassing the thermostat. This would cool the food more, whether it needed it or not.
However, this could give issues with the lubricants found in the refrigerant gas becoming to viscous for the compressor to start.
Guesswork! Based on no facts whatsoever
John

 

[JohnD]

Is it a fridge-freezer?

 

[ericmark]

I have in last two months replaced both fridge/freezer and freezer and until doing this I of course realised as the ambient temperature rises it will reach a point where it can't remove enough heat and will fail and I have always been careful on where I put the unit that there is enough free air to cool the condenser.

However as we went around the retail outlets we were advised again and again that if we wanted to use the freezer in a garage we had to select special models as many were unable to function correctly below 14°C.

I can see how a fridge or freezer can't control the food temperature as ambient approaches the control temperature as it only cools it will not heat the food. Well not strictly true for frost fee but the heater I suspect is not able to be used to control temperature.

With frost free I suppose the ambient temperature must be above freezing to allow the water from defrost to run out and not freeze but lower limit I would have expected to be just above freezing around the 4 to 8°C I say 8°C as the fridge can be set at 7°C so if ambient is 8°C then likely motor will only run for very short time.

But the limit set is 14°C and when making home brew I found my garage sits at around 10°C during winter months it is integral and the two gas water heaters for domestic hot water and central heating are in the garage so not that cold.

As to why some freezers can be used at as low as -14°C and others are rated as for use at 14°C or above still really no idea.