MACS Monthly Newsletter - 2021 - OCT8

Effects Of Ageing
The average age of vehicles on the road exceeded 11 years
some time ago, and among the reasons is that the bodies
have maintained their appearance and major components'
working life is very high. It used to be that cars of that age
were " rust buckets " or otherwise had obvious signs of decrepitude
and " always " had something wrong. Now we see
cars and trucks that are well over 20 years old that look surprisingly
good.
But when there's a not-obvious air conditioning failure, you
may have to look deep. A general issue is that you'll keep findHVAC
finally began to show its age and came into the shop
with the high-pressure cutout valve having blown open. The
technician saw that the fan clutch was inoperative and replaced
it and the front expansion valve.
He also replaced the high-pressure cutout valve and recharged
the system, but the pressures still kept going up, to
300 psi (and still rising) on the high side (and 50 psi on the
low side). Finally, the fan clutch engaged and the high side
pressure dropped to 200 psi, but no consistent cooling. The
condenser and radiator were surrounded by shrouding, but
no obvious signs of debris and there seemed to be good airflow
through the front heat exchangers, as viewed from the
top of the shroud. The technician pulled the expansion valve
to check for debris-here again, no debris.
A 27-year-old van that has the original HVAC and rear
Figure 11: Front-end shrouding for heat exchangers on
Dodge E-350 van limits ability to view condition of radiator
and condenser to just the tops.
ing things that are wrong, you'll correct them, and the system
may even work for a while, then stop. You start thinking, " Did I
miss something or is the problem something new? " The customer
may even wonder the same thing.
The vehicle in this case is a 1994 Dodge B-350 van with
more than 200,000 miles on the odometer. Vans and trucks
are often kept in service nearly forever, or so it seems. As you
might recall, 1994 was around the midpoint of the changeover
from R-12 to R-134a and vans, trucks and wagons were
manufactured with the R-12 system. Just three years ago, this
vehicle had received a " mid-level " retrofit to R-134a-fittings,
oil and replacement of the two receiver-dryers (front and rear
HVAC systems) and the front expansion valve. Recently, the
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.
October 2021
8
system, plus a retrofit could have almost anything wrong, including
the refrigeration system. But the symptoms still point
to the possibility of airflow issues. And with a full front-end
shrouding system in place (Figure 11), the technician could
see just so much, actually not so much. A close inspection of
the radiator was in order. But with the HVAC system, access
to the radiator starts with access to the condenser mounting
bolts, which requires removing the grille. Next, because the
transmission oil cooler
is built into the radiator,
the cooler lines have to
be disconnected and
plugged at both ends.
The radiator comes
out from the bottom
and then the problem
becomes apparent: a
thick layer of grassy debris
coats a substantial
section of the radiator
core at the bottom (Figure12).
This shouldn't
be a real surprise as
road debris is drawn up
to the radiator, not far
enough to be seen from the top, but enough to reduce overall
airflow to raise A/C pressures and blow open an old, weak
high-pressure cutout valve.
With the new radiator in place, the overall airflow increased,
Figure 12: Lowering radiator
out of front end of van shows
buildup of debris that wouldn't
be visible from top of heat exchanger.
and
the fan clutch engaged much earlier. A/C cooling on the
old van was now good enough to satisfy the customer. v
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
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MACS Monthly Newsletter - 2021

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