MACS Monthly Newsletter - 2020 - DEC1

Total Vehicle Climate and Thermal ManagementTM
By Paul Weissler, MACS Senior Technical Correspondent

December 2020

Winter Heating Issues
With winter on the horizon, you're likely starting to think
about dealing with customers complaining about poor heat.
Inasmuch as the average car on the road is over 12 years old,
many technicians have " a plugged heater " at the forefront of
their thinking, and if you look at the statistics, there's merit in
that line of thought. It's moved ahead of the " thermostat stuck
open " on the list of what-do-I-look-for-first.
The thermostat dropping down on the troubleshooting list
isn't just a matter of improved part quality, although today's
stats seem to be more reliable. Truth be told, stats often suffered
from deterioration of the coolant and their failure to close completely has been a longstanding issue. And although today's
cooling systems start out reasonably pristine, including nearlaboratory-level pure water in the anti-freeze mix, the extended
service intervals (100,000 miles and up) and the coolant mixing
with far-from-pure tap water for top-ups can change that picture.
However, the vehicle diagnostics on late models are programmed with a projected engine warm-up schedule, so if the
stat doesn't perform as expected, the computer will log a trouble
code, and even may turn on the check engine light. So, unless
the on-board diagnostics lead you to the stat, looking elsewhere
has logic behind it.
Every technician should understand that the higher efficiency
of late-model engines makes it difficult for them to produce
the kind of heat many motorists have come to expect. This is
particularly true with multi-speed and pulse-width modulated
electric fans. Fan operation that's fine for A/C operation in hot
weather may be too aggressive for cold weather. The fans normally should (and do) incorporate a strategy based on ambient
and coolant temperatures. However, the sensors may not have
the operating range for the fans to slow down or even turn off to
conserve cooling system heat in very cold weather, even though

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they're not logging any trouble codes. The
sensors
may
have had the
operating range
for cold weather
in their original
manufacturing
specifications,
but
normal
deterioration Figure 1: Winterfronts are normally
may have tak- seen as add-ons to the grilles of trucks,
en them out particularly diesels, which typically proof spec. There duce inadequate heat for cabin warmth.
is more than However, unlike the simple approach of a
one sensor in a piece of cardboard in front of the radiator
fan algorithm, or condenser, they are vertically slotted
and some sen- so there is some airflow to maintain some
sors may have cooling air through the front end heat
more impact, exchangers, particularly important with
so as a vehicle high cooling loads on warm winter days
accumulates and/or carrying/towing high loads.
mileage, the net
result is often unpredictable.
That's led to increased consideration of grille covers. These
were the historical choice to improve cabin heating on cars with
thermostats that tended to stick open (or just open early). In fact,
they often were just pieces of cardboard trimmed to fit and located at the front of the front-end cooling module.
The commercially-available grille covers are often really grille
guards-screens that are intended to protect the front-end heat
exchangers from damage caused by abrasive road film, includ-

ALSO INSIDE THIS ISSUE:
NO THERMOSTAT TO REPLACE - THE ACTIVE COOLING SYSTEM . .......................................................................... 4
WHAT DO YOU EXPECT? IT'S A DIESEL!........................................................................................................................ 6
THE FANS ARE RUNNING, AND RUNNING, AND RUNNING TOO FAST........................................................................ 7
ELECTRIC WATER PUMPS................................................................................................................................................ 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

December 2020

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 Monthly Newsletter - 2020

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