MACS Monthly Newsletter - 2022 - JAN8

the layer that it attached to. With no refrigerant in it, there
was no resistance encountered when trying to blow air
or flush through. But with the system charged up and the
compressor not running, the hose would have about 104
psi of static pressure inside (at 90°F). With the inner liner
coming loose, there was also some damage that was allowing
refrigerant to permeate through it and get to the
area between the inner liner and the adjacent layer it was
formerly attached to. When the compressor was turned
on, it immediately started reducing the low side pressure.
The higher pressure on the outer part of the inner liner
caused the inner liner to collapse and caused a restriction.
Based on the pressure readings of 135 to 140 on the high
side and 60 to 65 on the low side, it wasn't a total restriction,
but rather was a partial restriction (Figure 10). But the
60 to 65 on the low side gauge wasn't what the actual low
side pressure was at the compressor. That's because the
low side service port was located between the evaporator
and where the collapsed area of the hose was located. It
involves a bit of speculation, but if it had been possible to
take a low side pressure reading there at the compressor
it would have likely been in the low single digits or maybe
even in slight vacuum. See Figure 11.
Many compressor companies report a large number
of NTF (No Trouble Found) compressors when conducting
warranty analysis on returned units. These are units
which have been installed by shops and then determined
to be defective because the systems won't function properly,
and they are returned for warranty. In this case and
in many others, a lot of that could be avoided and a lot of
time and expense saved by utilizing more careful diagnostic
procedures and temperature testing.
We've covered a lot of ground here and the three most
import takeaways from this MACS Service Report are:
1. The further service ports are located away from the
compressor, the more likely it is that what is being displayed
on a gauge may not be the actual pressures at the
compressor.
2. Temperature testing needs to be utilized to locate restrictions,
but if there is a total restriction there will be no
temperature drop because there is no refrigerant flow.
3. Contact type temperature testing devices must be
used when doing temperature testing on A/C systems. v
Figure 11: If a pressure reading could have been taken between the location of the restriction in the suction line and
the compressor (extra port added near the compressor), it would have likely been in the low single digits or maybe
a slight vacuum.
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.
January 2022
8
Editors:
Production Designer:
Elvis Hoffpauir, 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
Richard Hawkins

http://www.macsmobileairclimate.org

MACS Monthly Newsletter - 2022

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