MACS Monthly Newsletter - 2022 - SEP2

If either of your meter readings is not as described,
THAT is the side of the circuit with the problem!
If the meter readings are good, then the problem
with the LOAD is not electrical. It 's a mechanical
fault you need to look for. A compressor clutch with
an excessive air gap, for example, or a solenoid valve
that is stuck in an open or closed position.
If your meter readings on the positive side of the
LOAD are the exact same as what you measured at
the battery or a perfect 0.00 volts, then the circuit
has no current flow. Either there's an open circuit OR
you forgot to turn it on. Same applies on the ground
side. Here are some more specific examples of common
meter readings and what the meter is trying to
tell you. (NOTE: For the following examples, the first
reading taken at the battery is the same at 12.6v).
See Figures 2 through 6.
Now listen carefully here. 12.3v on the positive
side of the LOAD and 0.30v on the ground side of
the LOAD is for illustrative purposes only. The key
to remember is that the positive side measurement
should be close to, but not exactly, the measurement
you took at the battery. And the ground side should
be close to, but not exactly, 0.00v.
I've been asked many times what the allowable
limits are for acceptable voltage drops. I prefer to
share that IF you have a THIEF in your midst, the
meter reading will be noticeably larger than the limits
I just shared. I've never had a resistance issue
that resulted in just a few tenths difference in meter
readings.
The perfect reading is a dead giveaway. No current
is flowing so this is nothing more than an Open
Circuit Voltage (OCV) reading. But since it is seen
on both sides of the LOAD, we know that the LOAD
is intact and is allowing the OCV to pass through to
the other side. Problem? Open circuit on the ground
side OR the circuit is not turned on. See Figures 7, 8.
Anytime you see a reading on the positive side of
Figure 2: Positive side 0.0v: No current flowing - open
circuit between the battery positive post and positive
side of load prior to meter placement.
the LOAD that is way out of the norm, that is a red
flag that this is the side of the circuit with a problem.
Somewhere on that side is a THIEF, a source
of resistance that isn't supposed to be there and it
is stealing voltage potential away from the load. In
fact, in this example, the LOAD is only getting a little
less than 6v. Remember what impact that has on
current flow? That 's right - it 's decreased and not
enough for the LOAD to do its job.
Figure 3 and 4: Positive side 12.6v. Ground side 0.00v: No current flowing - open circuit in the LOAD and/or between
the two test points (connector).
September 2022
2
MACS Service Reports
Pete Meier
Pete Meier

MACS Monthly Newsletter - 2022

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