MACS Monthly Newsletter - 2022 - AUG8

By adding another source, we now have
to use some of that voltage potential to
push through it too. And that will reduce
the available voltage to the LOAD. What
happens if you only give 6 volts to a 12
volt headlight? With resistance being the
same, lowering the voltage will lower the
current flow - below what the load needs
to work correctly. Make sense??
So, how do we find out if there is a thief
in the mix? Easy - we perform a voltage
drop test. Let me see if I can help you
pull everything that we've talked about
so far into understanding the idea of the
voltage drop test.
Remember what Kirschoff said? All
voltage potential will be used to overcome
all sources of
resistance in the
circuit. And the LOAD should be the major player,
right? So, if I apply, say 12.6v to the LOAD, it should
consume that voltage potential so that when I try
to measure what is available on the other side, my
Figure 10: One of the most obvious sources of unwanted resistance is
battery terminal corrosion. This vehicle is a 2013 Subaru Outback, which
would not crank over, leaving the motorist stranded at a local park.
meter should read nothing. That is voltage drop, and
that is how you'll find out where in the circuit your
problem lies.
In our next issue, I'll pick up where we left off and
dive into some details. But before I do,
I
Figure 11: Have fun practicing your circuit testing measurements!
All you need is a battery, set of test leads, a few light bulbs and a
voltmeter to get started.
want you to promise yourself something.
I want you to take what I'm about to show
you and try it in your shop as soon as possible.
Grab a battery, some wires and a few
bulbs (Figure 11) and build a circuit using
one of the bulbs as your LOAD and another
as your THIEF. Put the THIEF before the
LOAD and put it after the LOAD, measuring
the voltage (potential between the meter
leads, remember!) at different points of
the circuit so you can see what I'm going
to show you now for yourself. I PROMISE
that if you do this, you will have that " AHA "
moment and your electrical testing
ability will skyrocket.
Thanks for reading. v
MACS Service Reports is published monthly by the Mobile Air Climate
Systems Association. It is distributed to members of MACS and
is intended for the educational use of members of the automotive air
conditioning service and repair industry. Suggestions for articles will
be considered for publication, however, MACS reserves the right to
choose and edit all submissions.
Unless otherwise noted, all photos/art by author.
August 2022
8
Editor:
Production Designer:
Steve Schaeber
Laina Forcey
Manager of Service Training: Steve Schaeber
Mobile Air Climate Systems Association
P.O. Box 88, Lansdale, PA 19446
Phone: (215) 631-7020 * Fax: (215) 631-7017
Email: membership@macsmobileairclimate.org
Website: www.macsmobileairclimate.org
MACS Service Reports
Steve Schaeber
Steve Schaeber
http://www.macsmobileairclimate.org
MACS Monthly Newsletter - 2022

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