MACS Monthly Newsletter - 2017 - OCT4

MACS Staff

US Patent Office

Figure 5: MY2012-2017 Fiat 500 vehicles only use 1.7 ounces for total system oil capacity, and according to our records, it's the smallest amount of oil
used in any passenger car A/C system. Comparing this number to the model's
average 16-ounce refrigerant charge puts the ratio at just 10.6% for its Denso
SCSB06C Scroll.

Figure 4: Rear view of a Sanden scroll showing the position and location of
an oil separator in the rear head.

small gain in fuel economy improvement for one individual vehicle, but multiply that by the millions
produced each year, year after year, and things can
really start to add up.

Once the oil has been separated, the refrigerant
continues on its way out of the compressor, through
the discharge line and to the condenser. But the oil
drips down along the inside walls of the compressor to a sump or collection area where it can continue to lubricate the internal workings.
Several benefits are thus achieved. Since the compressor retains a greater amount of oil, there is less
of a chance that lubrication will suffer as refrigerant
charge gets lower over time due to leaks. And with
less oil in circulation, the compressor doesn't have
to work as hard to circulate the refrigerant through
the system. There's a double energy saving benefit
to this, because when oil coats the inside of the condenser and evaporator (particularly the evaporator,
where refrigerant is boiling), it acts like a thermal
blanket, reducing the amount of heat transfer that
can take place (which is perhaps one of the greatest
efficiencies gained by the device overall).
From another point of view, because there's not
as much oil circulating, the manufacturer doesn't
need to put as much oil into the system to begin
with (which saves money and helps to lightweight
the vehicle). In fact, some of these oil separating
compressors use alarmingly small amounts of oil,
leaving many technicians to wonder if the service
information they're reading is a typo or not. See
Figure 5.
Overall the environmental gains are perhaps
greatest when measured among the entire fleet of
vehicles that have switched over to energy saving
technologies such as these. Sure, it might be a very

October 2017

EPA's ROLE
The US EPA helps to further these energy-saving
technologies by offering CO 2 credits for improving the efficiency of air conditioning systems. Besides credits for things like reduced reheat (using
an eVDC compressor), default to recirculation (with
sensor feedback to control cabin air quality) and
blower motor controls that limit wasted electrical
energy (by using pulse width modulated controls
instead of resistor packs that generate wasted heat),
OEMs can earn fuel economy credits by using an oil
separator in their A/C compressors. For MY 20122016, the credit value (in grams per mile) for separating oil was 0.6 g/mi. For MY2017 and beyond,
that credit amount is reduced to 0.5 g/mi for passenger cars and raised to 0.7 g/mi for light duty
trucks.
But it's not an automatic credit that's given just because the oil separator is physically present. There
are several hoops the OEM has to jump through if
they want them, which begins with sending EPA
an engineering analysis that demonstrates the increased improvement of the system as compared to
a baseline design. For example, if Volvo wants to get
credits for the compressor in their XC90, they have
to show how much more efficient it is as compared
to a prior model years' system of similar design.
According to EPA documents, an oil separator

MACS Service Reports

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