All I know is they are great for drying the floor when the trailer has been washed out.
Let me get this right …
Your telling me that you open some little trap door of maybe half a square meter to vent an 80 cubic meter box ■■?
Anybody ever seen one going down the road with one open?
And yes you do need a door that big for a probe.A thermal probe is about 8 inch by 3 inch. and takes about 4 or 5 minutes to give a correct reading or do you have your ware house staff stand there holding the readout unit while they just put the remote thermocouple through the bloody door.
Bking:
Let me get this right …
Your telling me that you open some little trap door of maybe half a square meter to vent an 80 cubic meter box ■■?Anybody ever seen one going down the road with one open?
And yes you do need a door that big for a probe.A thermal probe is about 8 inch by 3 inch. and takes about 4 or 5 minutes to give a correct reading or do you have your ware house staff stand there holding the readout unit while they just put the remote thermocouple through the bloody door.
Well yes. Different continent I know, but we often received written instructions on our paperwork to have the door open when we reached a certain point south, especially with potatoes. I don’t really see what else they were for on our trailers because they all had a mesh over them behind the hatch so that you couldn’t reach in and steal anything etc, certainly nowhere to stick a temp probe through unless it was very small, 3 inches certainly would not have gone through.
Your all wrong, It’s for midget migrants to hop aboard at Calais 
Not all loads that go in fridges need chilling or freezing 
Some need nothing, others need heating, some just need to be at a constant temperature
Bking:
Let me get this right …
Your telling me that you open some little trap door of maybe half a square meter to vent an 80 cubic meter box ■■?Anybody ever seen one going down the road with one open?
Er yes
Bking:
Let me get this right …
Your telling me that you open some little trap door of maybe half a square meter to vent an 80 cubic meter box ■■?Anybody ever seen one going down the road with one open?
And yes you do need a door that big for a probe.A thermal probe is about 8 inch by 3 inch. and takes about 4 or 5 minutes to give a correct reading or do you have your ware house staff stand there holding the readout unit while they just put the remote thermocouple through the bloody door.
Yes, see them driving with them open all the time. And as for your point about probes, well in my 10 years of mostly fridge work I’ve never seen a probe that big and when they do probe it’s the product not the box temp. If the door is for this mythical giant probe why is the door on the front 3.5 metres up?
You stick to fixing things and I’ll stick to pulling fridges round, how’s that sound.
Bking:
And yes you do need a door that big for a probe.A thermal probe is about 8 inch by 3 inch. and takes about 4 or 5 minutes to give a correct reading or do you have your ware house staff stand there holding the readout unit while they just put the remote thermocouple through the bloody door.
I’m with Luke on this. Have never seen a thermal probe of the kind you describe, although maybe the firm I work for has yet to catch up on the latest refrigerated transport innovations . . . ?
We, and our customers, make do with the standard hand held thermometer with a 150mm long probe, which is about as thick as a knitting needle, so you can either put it between the boxes on a pallet, or you can take the temp at the centre of a product, using a specific test packet in instances such as processed meat. Either way the thermometer will normally give an accurate indication of temperature in a minute or so, no need for anyone to stand around waiting for long on the loading bay.
Of the 3,000 or so reefers our firm operates I don’t think I’ve ever seen a hatch on the rear doors of a single trailer. I have started seeing them on moveable single piece bulkheads, connected to the handle. Makes shutting the bulkhead easier as the air can escape immediately instead of having to go past the side seals.
~ Craig
We have them, told they are for fruit that is in the trailer for more than a few days as the fruit emits gas which can make the load perish quicker. I know that when we tip ipl at normanton with spanish loads they ask if we’ve had them open.
Bking:
Ventilation ■■? The fridge ■■■■■ in fresh air through the condensor then blows it through the evap unit to cool it.Then it ■■■■■ it out the front bulkhead vents.How much ventilaton do you want?
Thats why they tell you not to load above the red line so cold air can circulate.
They don’t ■■■■ fresh air, they ■■■■ air from near the floor of the trailer and blow it out the top.
Bking…FAIL 
Trailers equipped with door vent on curbside door or front vent
on roadside of front wall. The vent is used for trailer’s
ventilation. After discharge cargo every time, the vent should be opened for a few minutes to avoid vacuum damage.
See figure 5-4 and 5-5.
Page 15 here with pics 
cimc.com/cimc-usa/CIMC%20Ree … Manual.pdf
Well thats bking told
Mike-C:
Trailers equipped with door vent on curbside door or front vent
on roadside of front wall. The vent is used for trailer’s
ventilation. After discharge cargo every time, the vent should be opened for a few minutes to avoid vacuum damage.
See figure 5-4 and 5-5.Page 15 here with pics
cimc.com/cimc-usa/CIMC%20Ree … Manual.pdf
Yes this sounds right ,also the vacuum point makes sense when opening a fridge.
So they are called a vacuum ventilation door,not a small flap door in the door of a fridge door…Sussed.
nearly there:
Well thats bking told
Looking forward to old Burgers retaliation rant
If the door seals are very efficient, it is possible that condensing moisture will form a partial vacuum in the fridge. This makes opening the doors very difficult, so the little flap is there to release the vacuum.
The fridge recirculates the air that is already in the box. The space at the top and the gap under the pallets is needed for it to work efficiently.
The vacuum thing makes sense, changing temperatures will affect air density, which could ■■■■ the doors in to a degree. Although I have never had a problem opening fridge doors because of that. It also raises the question, why have them on the top front corners 
that can’t be for a vacuum surely
Some of our trailers have vents front and rear, the only time I’ve ever had them open is at the request of a customer and that has been when carrying chilled produce to reduce ‘sweating’
The vacuum thing makes sense in a clever technical kind of way, but to me it isn’t common sense, if that makes sense
There may well be a link on the internet explaining about vacuums and door opening procedures, but my own real life experience makes me think that’s a load of hot air (pardon the pun)
newmercman:
~ but my own real life experience makes me think that’s a load of hot air (pardon the pun)
It’s COLD!! 
Snowgo:
Bking:
Ventilation ■■? The fridge ■■■■■ in fresh air through the condensor then blows it through the evap unit to cool it.Then it ■■■■■ it out the front bulkhead vents.How much ventilaton do you want?
Thats why they tell you not to load above the red line so cold air can circulate.They don’t ■■■■ fresh air, they ■■■■ air from near the floor of the trailer and blow it out the top.
Refrigeration units remove heat (warm always moves to cold). The evaporator absorbs the heat from the box and the condenser rejects heat. The two components work together in that manner along with more components to make up the very complex refrigeration cycle. There is no transfer of fresh air from outside through into the evaporator. There are plenty of links on Google and videos on YouTube re: the refrigeration cycle.
The red line in the box is so the air inside the box can circulate the load. The refrigeration unit removes heat, from the box and the product, although the product should be at its required temperature when loading - the transport refrigeration system is designed to MAINTAIN its temperature. Shrink wrapping the bottom of pallets and stacking product too high restricts air flow so you’ll find the product closest to the bulkhead is cold, probably too cold, and then near the door your product will be above temp.
Regards the trap door - I’m not 100% sure but the vacuum comment is likely. Ever had your home fridge/freezer seem hard to open, or at the supermarket when someone has just closed the door and you go to open it and it’s like WTF? Low temperatures equal low pressures. If you’re running your fridge at -25°c the pressure inside will be low.
The temperature probe comment doesn’t make sense because when you tip your load the doors are open (after the fridge is turned off) - they probe the product, not the air temp - if the unit has just come off defrost it won’t be at -22°c. The fridge and datalogging equipment (if used) has to be calibrated annually so the company would provide that if necessary. Have any of you ever had your load rejected? They will more than likely mark the product with UV ink/dye so that you can’t go down to the nearest lay-by and bring the box/product down to temp and take the same product back… They care about the product temp…
Sorry for the story…
The vacuum argument makes perfect sense to me coming from a liquid & powder tanker background, what doesn’t make sense is the position of these little ■■■■■ flaps. What about the older fish trailers equipped with drains to let the water out, you could tell when you were about to overtake one by the smell of fish. A simpler idea would be to fit a simple ball valve in the floor of the trailer which would probably aid draining and drying after swilling out.
Obviously if there wasn’t any ventilation, you would not be able to set fire to a brown paper bag. Smells fishy to me!
If you underestimate the power of dust, temperatures, static, pressure, or vacuum, be warned! It WILL bite you on the bum.
