MACS Monthly Newsletter - 2017 - SEP1

Total Vehicle Climate and Thermal ManagementTM

September 2017

By Dave Hobbs - MACS Field Correspondent

CONTROLLING THE HEAT - HEATER VALVES IN THE 21ST CENTURY
ure out how it worked and why it was there. Close
off the flow of hot coolant to the heater core and
the entire evaporator / heater case will get cooler
in the summer allowing the A/C to cool more effectively. Somewhere in the 1990's we began to see
heater valves disappear on many vehicles. If I were
to guess why, I'd guess cost. Every OEM car maker
struggles to reduce costs anyway it can. If the cabin
temperature goes up a couple of degrees due to the
A/C evaporator competing in a hotter environment
with hot engine coolant flowing freely through the
heater core, so what? The benefit to performance
ratio has always been the big decider in automotive engineering. Like so many other technologies
we've seen over our careers, some ideas are recycled with new twists. Heater valves are one of those
technologies. If I were to guess again why heater
valves are making a comeback, my guess would
be to contribute to tighter fuel economy and emissions. The cooling system is being managed with
much tighter controls compared to just a few years
ago. Electric solenoid style heater valves can suffer
the same maladies as the old cable or vacuum diagram predecessors. They can freeze up (poor cooling system maintenance) and stick open (less A/C
performance) or closed (poor heater performance)
and of course leak like any other cooling system
component.

Dave Hobbs

Chances are you've been working on HVAC and
cooling systems long enough to remember heater
valves with cables or vacuum hoses leading to the
HVAC head. My journey as a tech growing up in
my father 's auto repair business began in the 1970's
when heater valves were pretty much on every vehicle equipped with A/C. Turn the A/C controls
to Max / Recirc and either a cable or vacuum line
activated the closure of a valve situated in a hose
leading to the heater core. (Figures 1 & 2) It was one
component we didn't have to take a class on to fig-

Figures 1 and 2: These conventional heater valves (vacuum operated on left
Fig. 1 and cable operated on right Fig. 2) are still in use on some vehicles today.
Good money makers (coolant leak sources) for the repair shop, their popularity waned a bit over the last few years. Tighter engine management (which
includes the cooling system) has brought them back in a different form - solenoids.

ALSO INSIDE THIS ISSUE:
BATTERY POWER LOSSES & ELECTRONIC MODULES .............................................................................................. 2
OUTSIDE THE BOX DIAGNOSTIC ALTERNATIVES ...................................................................................................... 6
THERE'S GOING TO BE A QUIZ?!?! ................................................................................................................................ 7

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

September 2017

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.

MACS Service Reports

Table of Contents for the Digital Edition of MACS Monthly Newsletter - 2017