How long would it take to chill a trailer from +13 to -20 and warm from -20 to +13 ?
Depends empty or loaded fresh,chilled,or frozen. Door openings New or used unit all trailers have different units so no hard or fast facts
I suggest 25 minutes on a good fridge, same setting all the way through, 10-15 degrees outside, with a fair wind blowing.
Temperature is still in the teens and falling after 20 mins, but one set to -28 seemed to already be there by the time I came back from a 30 minute break though, so I call that “done at 30 mins”.
I’m just splitting the difference of course!
An empty trailer, same setting all the way through, backed onto a lagged bay in freezer section, and a bit windy outside all seem to affect the cooling time.
With the doors closed, a good set of door seals (not found at supermarkets I’ve seen so far) works wonders too.
I might pick up a switched-off empty trailer, set it to -28, then set off to a cold store 25 miles away, and by the time I get there it’s fully down to the -28, and giving me the old “Cliff Richard” when I open the (rubbered) barn doors. 
The return air temperature may be -20 or whatever, but that does not mean that the fridge is holding the load at that temperature.
obvious question, WHY ■■?
Just curious
…someone forgot to change the temp on the trailer 
yep trying to defrost that load of beer lol
What the hells the point of running down an empty fridge to -21.Soon as you open the doors the cold air drops out and the evaporators freezes up due to moisture being dragged in with the warm outside air.Then it flips over to defrost and any cold you had in the box just leaks away.Good way to waste diesel though!
The mist you see at the rear of a reefer when you open the doors is caused by the cold air in the fridge bringing the outside ambient air down to its dew point and the water vapour in the outside air becomes visible as it turns back into water droplets.Warm air has more energy in it so can hold more vapour.
Who’s diesel is it anyway?
Better than getting a site ban for melting the ice cream!
I’ve always done it pre-cooled, and never had any problems.
The outside air is dampest when it’s also coolest, so there’s only a good exchange of atmosphere towards the rear of the trailer. If you’ve not set both zones working against each other, and kept the bulkheads up and out of the way on the cooling empty trailer, by the time you’ve opened the doors and backed onto the lagged coldstore bay, the temperature will still remain below freezing no sweat (you could say!) 
ASDADRIVER:
How long would it take to chill a trailer from +13 to -20 and warm from -20 to +13 ?
You’re an ambient driver! Leave the technical stuff to the chill drivers… Lol
Saw a driver trying to explain why he had brought in a trailer at -21 with 26 pallets of tomatoes on it…
mkb600:
Saw a driver trying to explain why he had brought in a trailer at -21 with 26 pallets of tomatoes on it…
I once set a fridge the wrong way around, the tomatoes were like snooker balls. Another driver went to collect frozen cakes, saw 22 on the fridge and cracked on. Shame the previous driver had run back cooking the trailer at +22 to melt ice.
Bking:
What the hells the point of running down an empty fridge to -21.Soon as you open the doors the cold air drops out and the evaporators freezes up due to moisture being dragged in with the warm outside air.Then it flips over to defrost and any cold you had in the box just leaks away.Good way to waste diesel though!The mist you see at the rear of a reefer when you open the doors is caused by the cold air in the fridge bringing the outside ambient air down to its dew point and the water vapour in the outside air becomes visible as it turns back into water droplets.Warm air has more energy in it so can hold more vapour.
You’d be amazed at how many clients wont load a fridge until It’s cold enough…
I used to switch the fridge on long before I got to the customer to load…
I once took a load of frozen to South Wales. When I had dropped it I was sent back to Evesham for fruit and told to run the fridge at +28 all the way. I heard after that they loaded the trailer with peaches and a lot of them were ruined because the floor was still frozen.
We run ours at -25 and are very rarely empty which means that on especially the older fridges we get a buildup of permafrost that would keep an Eskimo happy! Consequently on the rare occasions I’m gonna do a few hours empty I ramp the temperature up to max to cook the ice off.
I make sure to reset it before dropping it though, and most importantly make sure I’m stood to one side if I open the doors! 
the maoster:
I make sure to reset it before dropping it though, and most importantly make sure I’m stood to one side if I open the doors!
I know what you mean…
Bking:
What the hells the point of running down an empty fridge to -21.Soon as you open the doors the cold air drops out and the evaporators freezes up due to moisture being dragged in with the warm outside air.Then it flips over to defrost and any cold you had in the box just leaks away.Good way to waste diesel though!
I guess that’s why most decent reefer firms instruct their drivers to turn off the fridge before opening the rear doors and then leaving the fridge off if you’re tipping or loading on an ambient loading dock . . .
~ Craig
you should run it down to -18 /-25 before loading frozen to cool the cargo space . As above best practice says that you should switch off the fridge before opening the doors to avoid drawing warm air into the fridge . switch it off , open the doors back it on to the bay and then switch it back on again . If the loaders tell you to switch it off while they load or unload it - the balls then in their court.
beefy4605:
‘…best practice …’
I’ve found ‘…best practice…’ means diddly-squat to anyone when its every man, supervisor & company clerk simply wanting their shift to end.
In reality, no-one really cares (unless the company cabbage catches you red-handed 
) - so the default rules of ‘don’t rock the boat’ and ‘don’t get caught’ apply, as usual 