robroy:
Can you buy any cheap Chinese fridges anywhere?
Mine needs somebody with vast fridge base knowledge to repair it, nobody on here I’m told, …hmmmmm , so a cheap Chinese version may (or Mao 
) be the answer. 
What do you reckon ‘‘Adam’’?
I’ll need to continue UK Tramp ing to save the cash.
The best fridges are made in China.
But what is your problem?
Will your freezer not go below -4c? 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.
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.
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.
I have designed and worked on some of the most complex refrigeration plants on the planet, +4.0C is a very special temperature in refrigeration. The human body is made up of 75% water, an awful lot of food stuffs hold water content and so the 4.oC magic number is very relevant.
Industrial refrigeration is my field and I can tell you anything you want to know about it. I even posted all of my refrigeration qualifications on here at one time including my gold card status and ammonia handling certs. Cold storage plants do indeed freeze from fresh in large blast freezers holding 20 pallets or more, then placed into the cold storage warehouse set at usually -20. The frozen pallets still hold heat and it takes a lot of energy to hold the huge amounts of pallets frozen.
If you place pallets in the cold storage warehouse at a less temperature than the set temperature then you get problems with imbalance and the compressors work harder than they should work and using huge amounts of energy to pull these pallets down to temp. All depends on the numbers here but it takes aprox 18 hrs to freeze a batch of 20 pallets of meat for example to freeze -18 to the core. Once again this all depends on water and salt content of the produce. I developed a way of freezing meat down to -10 which is the temp needed for factory cutters and slicers to effectively slice frozen meat. Any way carry on regardless with all your own theories, I am sure you will be right in your own ways.
The food chain requirement for refrigeration at engineer and storage facility level is very high and scrutinised by auditors regularly, Then the transport side just lets it all down, nothing stopping anyone from driving a reefer which is mindless and the reason why the checks and the paperwork trail at each end have to be so high.
Also your load is temperature controlled, by using a MANUAL defrost cycle which takes around 45 mins to complete will blow warm air through the trailer. and effect the trailer temperature. Along with this warm air will be a high content of water vapour which once the trailer goes back into refrigeration mode will freeze up and form ice. If an automatic defrost then takes place because the sensors are detecting ice forming it will go into a defrost a second time giving a further 45 mins of warming the trailer again thus affecting the temperature graphs from the stored data which would show a temperature spike twice.
There are so many other reasons why you should not initiate a manual defrost just for the sake of it, it would take up way too many lines to write. Not trying to be clever over this like some snide replies. There are much better ways of avoiding ice build up whilst loading in the first place, a manual defrost is really a last resort. Not saying it shouldn’t be performed in some circumstances but certainly not as a routine for loading. The prevention is far better than the cure, hence anyone who drives reefers should in my opinion undertake training on temperature control. This is very evident by some of the questions and replies, Your safest bet is to just check your temp gauges regularly and leave the unit too look after the defrost cycles.
By interfering with the defrost cycles and not knowing what you are doing by initiating one without proper advice you are risking the load. As I say there is a procedure for loading and unloading of temperature controlled goods, I know this better than most because I am a fridge engineer to begin with and understand these cycles and problems. I used to train reefer drivers on the various methods of avoiding manual defrosting, this practice has sadly been dropped from most firms because of cost issues and the dumbing down of the job, at one time a reefer driver was trained and this should be brought back, possibly on the cpc as a module would be a very good step forward. Most transport companies TM also have no idea of refrigeration and the critical control of these goods, it is left up to the drivers like you with no real knowledge of refrigeration and the transportation of these goods and there is a lot of hear say involved, someone tells you to do something so you just do it without reason. Understandable as I say, not patronising anyone for it as it is probably the way it is nowadays. Minimum training to do the job to achieve a minimum cost.
On the point of initiating manual defrosts, there is a time and a place for them no question about that. It is not to be done as some have suggested whilst loading or unloading. Lets assume a few scenarios here where it would not be good practice.
Firstly lets say as per your example of frozen. Most loading bays that deal in both fresh and frozen will try to maintain a bay temp of 4 to 5 degrees. You rock up to the loading bay with your doors open and position yourself on the bay. In the summer months as the weather is now you will have a lot of dry ice flowing out of your trailer and onto the loading bay. Good for the temp issues on the loading bay but when you have 8 or more wagons doing the same thing, loading bays can resemble a scene from a horror movie with vast clouds of dry ice laying layers over the floor. Your frozen produce has started loading onto your lorry and the forklifts are flying in and out of your trailer. You will see the dry ice now swirling in and out of the back of the box. You now pop your box into defrost and the fans stop running. now more than ever you are getting more dry ice into your trailer as there is no positive blowing so this dry ice settles onto the floor and walls of your trailer. the temp warms up from the defrost and causes the dry ice to form water vapour which is now saturating the trailer. When the defrost cycle ends and you’re unit starts to pull down, your coils will be wet which is why the fans should have a delay whilst the liquid refrigerant is pumping around the coils to freeze this moisture before the fans kick in. because of the high moisture content now introduced into your trailer through the defrost cycle, you’re trailer will freeze this moisture making even more ice than you originally would have including the floor area. More chance of icing up the evap coils as well as any air vents much quicker. This is the original senario that someone commented on here as suggested doing. It would be much more beneficial to have defrosted the trailer before loading or if really necessary to leave the manual defrost until your load is fully loaded and the doors are shut and left for aprox an hour for the temp to stabalise. Then a manual defrost will do the least damage as far as your load temps and forming ice around the evap coils and chutes.
After you’re last drop it is good to cook the ice and clear the unit which is also a good practice, rather than a defrost by turning up the heat you will clear the ice and drains etc much better. The condenser coils in this instance can be a problem but depending on weather conditions will not be a real issue. The main thing to remember is NOT to initiate a defrost whilst loading frozen, also to keep the doors open to a minimum, when the doors are open, stop the fridge unit and start it up when the doors are closed. Keeping defrosts to a minimum is the key. Hope this helps and clears up any confusions regards manual defrosts. Leave defrosts to the auto pre programmed cycles and do what you’re doing now and you will have very little problems.
But the main issue in modern refrigation design is that although many ‘reefer’ units are made in China are of higher quality. A lot of the instructions are in chinese so this has resulted in me having to learn Chinese in order to become a master of my craft. As for buying fridges in China, PM me I have some great contacts in Shenzhen and I can get you a good deal. But the fact you have a dodgy fridge may be more down more to driver error which even high quality Chinese fridges cant account for.
Whatever floats your boat.
