MACS Monthly Newsletter - 2022 - SEP1

Service Reports
MOBILE AIR CLIMATE SYSTEMS ASSOCIATION ©
By Pete Meier, MACS Technical Correspondent
Three Steps to Diagnostic Success
In our last issue, we covered some fundamentals
and techniques you can use when tackling an electrical
problem. Now, let 's dive into some details.
something.
But before I do, I want you to promise yourself
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
and build a circuit using one of the bulbs as your
LOAD and another as your THIEF (Figure 1). 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 " A-HA " moment and your electrical testing ability
will skyrocket.
Preparing the Circuit for Testing
First, prepare the circuit for testing. It must be
" on " for this test to work. Current must be flowing or
there will be no voltage drop. If the component you
want to test only works when the engine is running,
start the engine. If testing a brake light, be sure
to step on the pedal. Testing the A/C compressor
clutch? Turn the A/C on full blast!
Now begin your testing by measuring the voltage
potential in your SOURCE and noting the reading.
Try to place your meter probes on the battery posts
if at all possible so we can verify the integrity of the
connection between the battery and its cables.
Next, leave your negative meter lead at the same
spot you just used, and place your positive meter
lead at the positive side of the LOAD as close to
the LOAD as you can get. We want to test the entire
path. Note the reading. It should be close to, but
not exactly the same as, the first measurement you
took. Why? Because there are a few small mouths to
feed between the battery and load; the wiring, the
splices, the connectors and so on. They will all take
a little, but none should take a lot!
Finally, move your positive meter lead to the
Figure 1: Follow along with us and 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.
ground side of the LOAD, again as close to it as you
can get. This time, your meter should read very little,
but not exactly 0.00v. Again, this is because there
are still some small mouths to feed on the way back
to the battery.
ALSO INSIDE THIS ISSUE:
Why Did the Compressor Lock Up? By Richard Hawkins, MACS Technical Correspondent .................................... 6
MACS Service Reports is the official technical publication of the
Mobile Air Climate Systems Association, P.O. Box 88, Lansdale, PA
19446. The material published in MACS Service Reports expresses
the views of the contributors and not necessarily that of MACS. Every
attempt has been made to ensure
September 2022
1
the accuracy of the content of MACS Service Reports. MACS, however,
will not be responsible for the accuracy of the information published
nor will MACS be liable in any way for injury, labor, parts or
other expenses resulting from the use of information appearing in
MACS Service Reports.
MACS Service Reports
September 2022
Steve Schaeber

MACS Monthly Newsletter - 2022

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