Why does my Engel 80 litre fridge takes ages to get cold, with nothing in it, it takes days too get cold

no
fixya site doesn'y do spares
contact engel service agent for spares

Depends on how often and long the unit is left open, rule of thumb, fridge 4 deg C, freezer - 18 deg C.

Contact Engel - Engel Website

If you hear a click every few minutes and a buzz / click then nothing, it would sound as if your compressor is gone, the water problem is the defrost drain pipe is blocked

we see a lot of this have the thermostate replaced they cost around $40 us

check the cooler/freon/

thermostat not working correctly

AUTOMATIC AC/DC CHANGEOVER: All Engel Fridge Freezers can be plugged into both AC and DC at the same time. The Engel is smart enough to use the AC while available and then automatically switch to DC when the AC is no longer working. It will also sense the resumption of AC power and automatically switch back to AC making it ideal for high hurricane areas and places where power disruption is common.
Read more: http://www.roadtrucker.com/engel/engel-12-volt-fridge-freezer-technical.html#ixzz2MvRL2xrC

fully defrost it 48 hrs with the doors open and that can often cure it.

i need a schematic diagram of a fridge