Refrigeration works by drawing up warmer air that passes around your product up into the lower side of the evaporator ,this work is carried out the by evaporator fans.This warmer air is pushed passed the evaporator core and out over your product at a slightly lower temperature,this cycle continues slowly lowering the temperature until it reaches the set temperature.

Loading therefore is vital to the operation of your refrigeration unit allowing correct flow of air around your product.The alternative is that you block this airflow keeping cooler air from the evaporator at the evaporator end of the compartment.

So keep space above,to the sides and to the bottom of your product by use of pallets or other means.Many larger trucks have airflow floors allowing air to pass under the product.The down side to incorrect loading is that when you open the back door to load or unload warmer air enters and is then trapped in the rear ,warming up the product to the rear,again not allowing airflow to the front where it needs to flow through the evaporator.

When unloading try to use the side doors as the rear doors are usually larger allowing more warmer air to enter.Turn off the refrigeration unit when opening doors as the fans will blow the cold air out or use door curtains.

Internal walls with fan kits allow temperature variations,freezer in the front and chiller in the back.

The larger diesel stand alone systems such as Thermo king/Carrier /Zanotti to name a few ,all have a main Refrigeration compressor.This compressor is powered by a small say 4 or 3 cylinder diesel engine for example via belt drives or gear drives ..This same compressor is, when connected,driven by a large usually 3 phase electric motor .So 1 compressor driven by 2 separate power sources when required ..These high end Refrigeration units come with multiple sensors to detect if the  electric power drive has failed and will start the diesel engine to keep things cooling in the back .A very handy thing to have ..These high end refrigeration units have many other sensors that monitor many functions ,,but we are discussing Electric stand by in this post .

Important note that when you have your unit above running on electric stand by unattended,say overnight ,that as noted the electric power fails for any reason ,then the diesel engine drive will start ,so don’t have your vehicle sitting anywhere that is exposed to exhaust fumes  .So these units are as i said high end and made of some of the best available engines.parts etc available on the market and of course they come with the price tag to match ,,,but if your hauling expensive product you cant go any other way/Keep in mind these units are big and heavy and only suitable for say 6 to 26 pallet type applications .

Now we come to the smaller off engine drive with an independent Electric stand by unit .These Refrigeration units are driven by the vehicles engine.And the Electric stand by is mostly independent from the  vehicle ..

Normally a separate compressor is used ..You will find that these days a compressor called a danfos type is used these are a highly reliable enclosed rotary compressors and are wired in to 240 volt /10amp that can be run off your normal household plug .These are a commercial brand and high quality .When purchasing these ,they should be completely independent and  not have any affect on your vehicles systems .

There is another type of electric stand by available that incorporates another engine driven type compressor and also has a small electric motor  that drives this compressor ,they do work very well up to a point ,,,as the compressor cycles the gas builds up pressure this causes the compressor to lock making it harder for the smaller electric motor to drive the compressor .The electric motor starts to overheat causing fuses to burn out and circuit breakers to trip out .

Many operators will be found running the engine on there truck whilst the vehicle is sitting stationary to keep things cool rather than plugging in to an electric power source ,understandable if you don’t have electric power .But keep in mind that most of these types are not designed to operate this way for extended periods .,You will flatten your battery and given the lack of air flow over the evaporator .the unit will heat up and cause damage  as they are not designed wholly for this .(Check with the supplier)

Do your homework when purchasing electric stand by with your refrigeration units ,,It pays in the long run and re sale value will be higher

You can have a poorly built and insulated body and overcome this by fitting a high output Refrigeration unit.The same can be said in part for a Refrigeration unit with poor Output and a high quality Insulated body .
But the best way to deal with this is to have both working in harmony ,or as we like to do have the refrigeration slightly overspec ..as in the Refrigeration unit say the next size up from your needs .

Of course Transport refrigeration as opposed to Static/Fixed installation such as your fridge at home are not subject to the varying Temperatures experienced by a vehicle constantly moving in the atmosphere ,so therefore subject to changing conditions.There is also the problem with the vacuum that is created at the immediate rear of all vehicles as there moving forward.This of course creates a high and low pressure areas ,and if your door seals are not up for it ,you will rapidly lose cold air out the rear doors..This is a very common problem ..Stay tuned for more topics such as ,Loading,Electric Stand by ,Cool down times ,Servicing,Refrigeration and body types ,whos is the best and why