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|
| Conventional
manifold gauge sets used to service and test auto A/C systems include a low
pressure 'compound' gauge. It's called a compound gauge because it provides
a pressure reading as well as a vacuum reading. When you take a close look
at the gauge, it's easy to see that the 'level' of vacuum is really not that
accurate... no matter how much you spend on the gauge set. |
| Can
you rely on your low side manifold gauge? |
 |
This
is a close up look at the vacuum scale of a conventional low side manifold
gauge. We've added the 'red lines' to show just how difficult it really is
to tell what level of vacuum you're reaching.
The
scale on the gauge has a green line for every 2" of vacuum. When you compare
that to the thickness of the needle, it's easy to see that the needle itself
is at least the same thickness as 1" of vacuum. In short, you can't rely
on the compound gauge for accurate vacuum tests. It's better detailed
in the micron vacuum chart below. |
|
|
|
| A
close up look at 'micron' vacuum readings |
| Reviewing
the chart below, we can quickly see that using the manifold gauge for
an accurate vacuum reading is simply not reliable. Consider that 29.14" of
vacuum (as shown on your manifold gauge) would only be 20,000 microns. 29.89"
of vacuum would be 750 microns. With a conventional manifold gauge only,
you simply can not see the difference. After all, the gauge needle itself
is as thick as 1" of vacuum!
Using
the micron vacuum gauge for our tests allowed us to clearly see how each
vacuum pump performed before and after the vacuum pump service. |
%
Vacuum (Percent) |
Microns
|
Inches
Mercury Gauge |
0 |
760,000 |
0 |
97.4 |
20,000 |
29.14" |
98.7 |
10,000 |
29.53" |
99 |
7,600 |
29.62" |
99.9 |
1,000 |
29.88" |
99.9 |
750 |
29.89" |
99.99 |
100 |
29.916" |
99.999 |
10 |
29.9196" |
100 |
0 |
29.92" |
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