Revision Date – 15/07/2020
page 22
8 CHECKS AND TESTS
8.1 Vehicle wiring system
It is important that the wiring system is capable of carrying the required load to power the fridge freezer.
The accessories wiring system in many vehicles is not adequate for such a task. This is particularly true
in the rear cargo space of many modern four wheel drives. In some vehicles, these circuits are also
connected to the ignition switch and will not supply power if the ignition is turned off.
Measuring the voltage across the battery will not give a true indication of the voltage being supplied to
the fridge. Any voltage readings must be taken at the fridge supply socket with the fridge running. This is
because any voltage drop caused by losses in the system must be accounted for. Without the fridge
running, there will be no load on the circuit and it will not be possible to measure the voltage drop.
Voltage drop is the difference between the voltage readings taken at the fridge supply socket with and
without the fridge running. It is calculated using the formula shown below.
NOTE: In some 12V vehicle wiring systems, the voltage drop between the battery and the rear
factory accessories socket can exceed 2V DC.
It is important that the vehicle is not running while these voltage readings are taken. If the vehicle is
running, the readings will be the supply voltage from the alternator and not the voltage from the battery.
To check the vehicle wiring system, ARB recommend using a voltage drop tester. The voltage drop
tester will simulate the start-up conditions of the Compressor. These voltage drop testers are available
from ARB and have been specifically built to simulate the running of an ARB Fridge Freezer (all models).
The procedure for testing a vehicle wiring system using a voltage drop tester is given below. Suggested
actions based on the results of the voltage drop test are given at the end of this procedure.
VOLTAGE DROP TEST
Purpose:
To test the vehicle wiring system for voltage drop under a simulated fridge freezer load.
Procedure:
See below
Turn off the vehicle’s engine.
Turn off the vehicle’s ignition.
Insert the plug from the voltage drop tester into
the fridge/accessories supply socket.
Voltage reading at
supply socket without
fridge running
Voltage reading at supply
socket with fridge running
Voltage drop between
battery and supply
socket
=
-
