MACS Monthly Newsletter - 2020 - DEC3
nissan-techinfo.com
Figure 5: This diagram from a 2015 Nissan Pathfinder shows the typical two-relay circuit for a PTC heater.
guard has to come out at the end of winter, or summer overheating is likely to result.
Bye-Bye Volt
The Chevy Volt was taken out of production in 2019 as GM
decided to put its focus on other electrified models, such as the
battery electric Bolt and mild hybrids in its Buick line. So, as
GM's interest in the Volt has waned, keeping the vehicles on the
road falls to independent garages.
As we head into winter, that raises the question of the heater.
The Volt has an engine, but like other vehicles in its class, that
engine may not run much of the time, so heat is often produced
primarily by its PTC electric heater. If the motorist has turned on
the heat, the engine should run in cold weather, even if the battery pack was charged prior to starting the car. But even with its
The PTC Heater
December 2020
acdelcotds.com
On many late models, a PTC (positive temperature coefficient)
heater (Figures 3, 4) is built into the HVAC system to provide
cabin heating for very cold weather, not a practical approach for
a car without an OE installation. But if a light-duty vehicle has
a diesel engine or is a gasoline-electric hybrid, it's likely to have
a PTC heater in addition to whatever heat the engine coolant
produces. A PTC heater also produces some heat on a cold engine start, as it gets turned on immediately as soon as the battery
produces enough juice to get the engine running. In addition,
the vehicle electronics perform a battery condition test to ensure
the battery's overall condition is good, will accept a charge and
the charging system is capable of maintaining it.
Unlike a conventional resistance heater, the PTC is a solid-state
device that is current limiting. It operates at a much lower temperature, so it has longer operating life. The PTC is at the heart
of a straightforward fused two-relay circuit (Figure 5) from
the heater-A/C module, and in a hybrid is controlled by the
HVAC amplifier (control module). So, diagnosis generally
comes down to a fuse or relay, or occasionally of course, the
amplifier. Like any computer-control, however, the amplifier
relies on inputs from the engine coolant temperature sensor,
ambient temperature sensor, alternator load/battery state of
charge and HVAC control panel heater setting. So, a scan of
all the sensors, which should be part of any thermal system
diagnosis today, should precede any thoughts of replacing
the heater or amplifier.
Figure 6: Auxiliary electric pump is used on Chevrolet
Volt, to circulate coolant for cabin warmth and to cool
power electronics and the battery pack, as the engine
does not run much of the time.
3
MACS Service Reports
http://www.nissan-techinfo.com
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MACS Monthly Newsletter - 2020
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