So subj,
The scenario is: you load up chilled products, its +25c outside, so no matter what the temperature was in the trailer, by the time its loaded it is +16c inside. Your running temp is supposed to be +4c
Will the fridge freeze the front pallets if i set it on +4 straight away? Or should the temp be gradually decreased manually say every 2h by 3c?
Is this a trick question?
The fridge lowers the ambient temp of the trailer allowing it to keep frozen stuff frozen or will over time freeze any non frozen stuff inside it.
You collect a load and set it to the temp required by the customer and leave the temp and crack on keeping an eye on the temps whenever you get the chance to make sure it is correct.
Well, i wonder if it is more complicated.
I heard rumors someone got a claim as in my scenario the fridge went on full blast and frozen the front pallets. Obviously if you want to drop from +20 to +4 the fastest way is to get -20c air in
Priest:
So subj,The scenario is: you load up chilled products, its +25c outside, so no matter what the temperature was in the trailer, by the time its loaded it is +16c inside. Your running temp is supposed to be +4c
Will the fridge freeze the front pallets if i set it on +4 straight away? Or should the temp be gradually decreased manually say every 2h by 3c?
You don’t make any sense at all?
Why would anything freeze if you set it at 4c?
Set it at -20 it will freeze
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There’s usually a nice sticker inside the trailer showing how the air flows.
Assuming you haven’t dropped the divider(s) down then the whole of the trailer will equalise to the same temperature. If it’s +25 outside before loading and the customer wants it transported at +4 then run the empty fridge at +4 to pre-chill it before you back onto the bay and start loading. If the temperature rises during loading either run the fridge at +4 to maintain temperature or the onus is on the loaders if they want the fridge turned off while loading.
Well it is possible to freeze pallets by setting the temp too low for the product. But if you set it at 4° for example it will blow cold until the air temp is 4° so no it wont freeze anything.
Right so are you saying the blown in air temp is never going to be below the set temp?
Priest:
So subj,The scenario is: you load up chilled products, its +25c outside, so no matter what the temperature was in the trailer, by the time its loaded it is +16c inside. Your running temp is supposed to be +4c
Will the fridge freeze the front pallets if i set it on +4 straight away? Or should the temp be gradually decreased manually say every 2h by 3c?
Hi Priest,
It might be helpful if you were to tell us whether the “chilled products” are already at the correct temperature at the time of loading. 
If the load and your fridge are both at the correct temperature first, the fact that you opened the fridge for loading and then closed it straight away afterwards will not be a big deal.
When I was on fridges (many years ago) some of the exporters didn’t always have the load at the correct temperature at the time of loading, so there was one occasion when I arrived at a place to deliver, but the load was rejected.
The reason for rejection was that the load (frozen Dutch chips) was not at the correct temperature when the goods-in guy used a temperature probe at the destination in the UK.
There was an enquiry, but both my boss and I were in the clear because I took the goods-in guy to the thermograph and put the chart in his hand there and then with the fridge still running. The thermograph chart showed that I’d (correctly) got the fridge to the correct temperature before loading, and that the fridge hadn’t been turned off for the whole journey.
Priest:
Right so are you saying the blown in air temp is never going to be below the set temp?
The fridge unit will blow as cold as required to get the air temp down to the set point. It acts in the same way as your aircon on your car. It lowers the air temperature. The air blows above the pallets mostly unless they are very high pallets.
Priest:
Well, i wonder if it is more complicated.I heard rumors someone got a claim as in my scenario the fridge went on full blast and frozen the front pallets. Obviously if you want to drop from +20 to +4 the fastest way is to get -20c air in
Really the trailer should be pre-chilled before loading. Of course they generally never are
Maybe it will get cooler quicker if the desired temp is 4c & you set it to -20, I guess the air coming in will be cooler?
Yes probably a danger some stuff near the air intake will be frozen so no point, just set it at desired temperature.
Once the doors are closed it should get to temp pretty quickly though.
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Priest:
Right so are you saying the blown in air temp is never going to be below the set temp?
A very good point… I don’t know the answer to this.
dieseldave:
Priest:
Right so are you saying the blown in air temp is never going to be below the set temp?A very good point… I don’t know the answer to this.
I would hazard a guess (not being a fridge engineer like uktrump lol ) here but yes the air being blown will be lower than the set point, based on the set point it needs to lower the temp as quickly as possible for the size of the trailer or the amount of the load. The less pallets there are the harder the temp is to bring down and maintain. The more full the trailer then bringing the temp down or maintaining it is easier. How low the refrigerant can cool the air though is a hard one to say for sure. But I doubt the air temp coming out is as low as the max set point of - 30°.
the drivers role is to set the required temp and then ensure the temp vever varies allowing for the + or - tolerances on the trailer and also depending if its constant set,or intermittant.
itl go above and below slightly to ensure the average is what its set at.
any rejections then the dude comes out to the motor and downloads the data
to see who pays for the claim.
so long as it roughly stays around the set temp then anything else is outside your remit.
You cannot freeze any produce with a fridge set to +4oc. If the outside temp is above +4 or any other temp above freezing. The airflow is still 4.oC and will have a set temp range of + or - 2 max. If the produce going into the trailer frozen then it would start a defrost. Position in the trailer makes no difference as to whether or not it can freeze. It definitely 100% cannot. If you have a trailer that can freeze produce set at 4.0C then it is a magic trailer. Icing up of the evaporator coils does not happen either at these temps. Only way this is possible is if the temp sensor probes fail and your trailer goes into a freeze mode by mistake or you have set a negative temp on the unit instead of a plus temp. Chilled ambient max temp is always + 5.oC and +3.oC giving a two degree differential. The differential to freeze has to be a 10.oC differential from the evap coils. Therefore impossible. Take this from an expert. Happy to help.
dieseldog999:
the drivers role is to set the required temp and then ensure the temp vever varies allowing for the + or - tolerances on the trailer and also depending if its constant set,or intermittant.
itl go above and below slightly to ensure the average is what its set at.
any rejections then the dude comes out to the motor and downloads the data
to see who pays for the claim.
so long as it roughly stays around the set temp then anything else is outside your remit.
Correct. the differential is two degrees. The temp has to be checked on the goods on the loading bay which should be +3 to +5.0C although rarely achieved depending on loading doors open and outside temps etc. Trailer should be already at temp at the time of loading, once again difficult when the doors are open and loading is taking place, temp data of fridge is recorded throughout its journey. Any deviation found within the unit is not the drivers fault if he has checked what the trailers gauge is reading.
simcor:
dieseldave:
Priest:
Right so are you saying the blown in air temp is never going to be below the set temp?A very good point… I don’t know the answer to this.
I would hazard a guess (not being a fridge engineer like uktrump lol ) here but yes the air being blown will be lower than the set point, based on the set point it needs to lower the temp as quickly as possible for the size of the trailer or the amount of the load. The less pallets there are the harder the temp is to bring down and maintain. The more full the trailer then bringing the temp down or maintaining it is easier. How low the refrigerant can cool the air though is a hard one to say for sure. But I doubt the air temp coming out is as low as the max set point of - 30°.
Correct and incorrect here, when dealing with frozen produce, if you want to freeze with a temp of minus 20 then evaps will need to be set by an engineer to blow at -30 to achieve this. If you want to freeze at minus 30 then we set the evaps to blow at minus 45. This is warehouse storage but the principle is the same for a trailer. When you set to freeze at minus 18 on your panel, these settings have already been set in by an engineer to blow at a cooler temp. You are only setting the temp that you want the goods to freeze at, the complicated calcs have already been done for you by people like myself. Ambient is similar but with a much higher margin to compensate. Refrigeration is very complex and as engineers we shield you from all of the complicated parts of it and mainly why we are in high demand. Also what may surprise you, it is harder to maintain a frozen temp when a trailer is full, a lot of heat is still present in frozen goods. Blast freezing becomes even more complex with been able to freeze produce such as burgers etc within a minuet or so.
You wont freeze the…
Front pallets, you’ll freeze the tops of all the pallets loaded, the ones towards the front getting the worst of the cold air. If you ever load soft fruits and load them too hot, you’ll ‘burn’ them at the set temp that’s too low for the product as it’s loaded.
Fridges are designed to maintain the temperature of the product loaded onto it. No way in hell you’ll get cargo loaded ‘hot’ down to temp in a few hours in the UK. It is possible to bring cargo temperatures down over longer periods of time by ‘stepping down’ temp setting ie; drop 2 degrees C every 3 to 4 hours and so on.
I’m lucky, all the chill I load is done at our own factory so loading point temperatures are not my responsibility.
I still carry a lazer temp probe though.
The way I see it, if I’m loading product for a third party, I will know before I get there what temp my firm want me to load it at. No last minute arguments at 21:00 on the loading dock with their line manager. ‘If it’s not +4 degrees, my boss say’s I can’t load it’. Any thing out side of the discussion is ‘no worries, I’ll call my boss’.
Short answer, yes, a fridge can freeze chilled stuff. Just as well as it can ripen bananas at +15.
yourhavingalarf:
Short answer, yes, a fridge can freeze chilled stuff. Just as well as it can ripen bananas at +15.
This is exactly why you shouldn’t pay any attention to just anyone… Stick something in your fridge at home at 4 degrees and see how long it takes you to freeze it. 
Complete and utter rubbish.
It’s possible on some fridge units to see the temperature of the air going in and going out of the trailer, depends on the brand of unit.
Have a look in the settings on the front
I have looked at this before when a trailer is struggling to get down to -20 to see what temp the air is coming in.
Some of our old trailers can barely make it to -15 which is the point at which we are allowed to leave with it…
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UKtramp:
yourhavingalarf:
Short answer, yes, a fridge can freeze chilled stuff. Just as well as it can ripen bananas at +15.This is exactly why you shouldn’t pay any attention to just anyone… Stick something in your fridge at home at 4 degrees and see how long it takes you to freeze it.
You’re a fridge engineer…
You say?
You know ■■■■ well I’m using the word fridge to describe a reefer trailer (you do know what that is don’t you?).
Set the fridge trailer to minus 27 degrees C and put a strawbwerry in it and see what happens to it.
Witness the two chilled loads we had frozen by mistake last year in ‘fridges’.
Complete and utter rubbish you collosal dumb ■■■■.