MACS Monthly Newsletter - 2022 - SEP4

Figure 11 and 12: Positive side 12.30. Ground side 4.72v.
For Figures 13 and 14, consider this: Are we measuring
on the ground side of the LOAD OR are we
measuring on the positive side of our THIEF?
The reading of any voltage significantly more than
a few tenths means there is another source of resistance
on the ground side of our LOAD. And just like
before, it is stealing away from the voltage potential
the LOAD needs to function.
That, my friends, is Voltage Drop Testing 101 and
I hope it helps you become more confident in your
electrical troubleshooting. But, like any other new
skill, you have to practice to become competent.
So take a battery, some wiring and a few bulbs and
start measuring!
Using Current as a Troubleshooting Tool
Don't you love when a customer pulls into your
shop and says, " My A/C isn't working! " And if you're
like many of the techs I meet, you confirm their concern
by setting the A/C on full blast and peeking at
the compressor to see if the clutch is engaged and
the compressor is running. When it 's not, the next
step is to determine why.
At this point, assumptions are now made and pursued.
One of
the most common is the assumption
that the refrigerant charge must be low. Others will
attempt to bypass the relay to see if the compressor
engages. Add in the fact that many compressors
are mounted low in the engine compartment and not
easily accessible, I think you'll agree that there must
be a more efficient way to determine the cause, or at
least get us pointed in the right direction.
And I think I have one for you. Use current to diagnose
the problem (Figure 15).
In systems using a conventional fixed displacement
compressor driven by a mechanical compressor
clutch assembly, the clutch is engaged by the
ECM. To be a bit more specific, the ECM first verifies
that the conditions required for A/C operation are in
place before completing the circuit to the compresFigure
13 and 14: Are we measuring on the ground side of the LOAD OR are we measuring on the positive side of
our THIEF?
September 2022
4
MACS Service Reports
Pete Meier
Pete Meier

MACS Monthly Newsletter - 2022

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