MACS Monthly Newsletter - 2018 - JAN1

©

Total Vehicle Climate and Thermal ManagementTM

January 2018

By Paul Weissler, MACS Senior Field Correspondent

When the high-side pressures kick up beyond the normal
range, the A/C performance dies and in severe cases, the pressure relief valve pops open and we add in refrigerant loss to the
job ticket. But first, we understand that the pressures have to be
brought down to normal. Most technicians start with airflow.
Nothing wrong with that train of thought, but let's keep an open
mind. Here are three cases, each with a different root cause.

from quality makers and suppliers), although a defective
part can always occur even
with reputable makers. Much
of the time, any issue is plugging with compressor failure
debris, but here we have an
exception. It was clearly a
defective unit, and because
we didn't see the unit, we'll
speculate an internal blockage and/or poorly-attached
fins were the likeliest issues.
However, the PT Cruiser
is a "sensitive" model, with
A/C cooling that "just met"
Figure 1: If watering down a conthe factory performance "bodenser reduces high-side pressures to
gey." And the area in which
normal or near normal and possibly
the car was being operated
also restores A/C performance, that
was the steamy southeast. So
seems to point to low airflow or possibly a condenser issue.
even though a new OE condenser didn't suddenly produce refrigerator-like temperatures, the high-side pressures did
drop to a bit over 200 psi and the cooling improved significantly.

2002 Chrysler PT Cruiser
When high-side pressures jump, the first thing many shops
do, as we've noted, is make sure there's good airflow. It seemed
to be good on that PT Cruiser, and with no signs of a debris
buildup at the front. However, with the service valve on the discharge line or compressor, a blockage in the line or within the
condenser became a reasonable suspicion. In this case, the car
has an orifice tube/accumulator system. The desiccant bag is
not in the high-side refrigerant lines, but in the low-side accumulator, so a ruptured bag resulting in a plugged liquid line was not
on the possibilities list. Just about everything on the HVAC had
been replaced at some point: evaporator, compressor, condenser,
liquid and discharge lines, radiator and electric fan assembly. So,
we'll operate on the hopeful assumption that any debris from
the compressor is not likely to be an issue. But above fast idle the
pressures skyrocket, and eventually the high-pressure cutout
disengages the compressor (around 375-450 psi).
Spraying water on the condenser (Figure 1) got the pressures
to drop closer to a normal range and A/C cooling to resume,
which makes the replacement condenser an object of suspicion.
After all the parts replacements, owners of a 16-year-old PT
Cruiser are probably a bit averse to spending any more money
than absolutely necessary, so we wouldn't be surprised if a discount non-brand was sourced. We find that most complaints
about aftermarket heat exchangers are unjustified (if they're

2008 Chevy Silverado HD
With the 6.6-liter Duramax diesel V8, this pickup produced
another high-side pressure issue, but with a very different vehicle history. Here the A/C also doesn't blow cold air, but the
problem really is pronounced only at idle. Heavy-duty trucks,
perhaps not nearly as much as bigger trucks, do spend a lot of
time idling while they're loaded and unloaded, so idle operation
is important.

ALSO INSIDE THIS ISSUE:
THOSE DECOUPLER PULLEYS ...................................................................................................................................... 4
FOR THE UMPTEENTH TIME: HOW THE CIRCUIT WORKS, BUT NOT SO SIMPLE ................................................... 4
MORE ON SMALL CANS ................................................................................................................................................... 6
BUT WHAT IF THERE'S A LEAK? ..................................................................................................................................... 8
MACS Service Reports is the official technical publication of the Mobile Air Conditioning Society Worldwide, Inc., 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

January 2018

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
Worldwide be liable in any way for injury, labor, parts or other expenses resulting
from the use of information appearing in MACS Service Reports.

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MACS Service Reports

Steve Schaeber

HI-SIDE PRESSURE "OUTTA SIGHT" - THE CAUSES VARY



Table of Contents for the Digital Edition of MACS Monthly Newsletter - 2018

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https://www.nxtbook.com/nxtbooks/macs/servicereports_2018
https://www.nxtbook.com/nxtbooks/macs/servicereports_2017
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