MACS Service Reports - 2016 - JUN4

And because you will have the hand-held, you can get a new
R-1234yf recycling machine without a built-in identifier, so it will
cost less. Or if time passes before you see enough R-1234yf volume and your R-134a machine is not in quite the great shape of
years ago, you can get J3030 equipment, also with just the USB
port configuration instead of the built-in identifier.
Interestingly that current version of an R-1234yf machine,
with the USB port for a signal from the compliant identifier, is
not noticeably more expensive to make than the "unlocked" machine made to the older standard. The only extra cost would be
for a circuit board and the USB port, which fall into the pocket
change category. And as a practical matter, we would not be

surprised if a salesman pitching the "unlocked" machine tells
you he wants a bit more (or offers less of a discount) for the "advantage" it offers.
Just a final note: these days all you may see the recycling machine makers selling are machines with built-in identifiers (FIG.
7). The reason is that their major market right now for R-1234yf
equipment is from car dealers, who must buy machines with
built-in identifiers and printers, necessary so they can collect
warranty payments from the car makers. However, you can
order your machine without the identifier, just the USB connection--negotiate your best deal. ■

SHOULD YOU SAY GOODBYE TO THAT "RULE OF THUMB" ON CONDENSER TEMPERATURE DROP
TESTING - AND THE REASONS WHY EVERYTHING'S CHANGED

June 2016

MazdaUSA

It's been an honored rule of thumb for decades, although
the range of the rule has changed somewhat over the recent
years. And now we may have more significant limitations.
We're talking about normal temperature drop across the
condenser (inlet from the compressor discharge line, outlet
going to the high-pressure/usually liquid line), which not
too many years ago was 15-25° F. Then as condenser efficiencies went up, we raised the range to 20-40° F., and more
recently to 20-50° F. Anything beyond that was a sign of a
restricted condenser. Now, it's not so likely an indication.
The temperature drop through a condenser depends on
a number of things: 1) the discharge temperature from the
compressor; 2) the refrigerant flow through the condenser;
(3) the efficiency (basically a design factor) of the condenser;
(4) ambient temperature, (5) or if in the shop, also the electric
fan operation and front end airflow. This last item can be a
big variable if there's a strategy that holds off operation of
the highest fan speed while you're checking the temperature
drop.
And the last (but probably most critical item on our list):
can you actually measure temperature drop SOLELY across
the condenser? A case we discuss later in this article: MACS
tech trainer Tim Iezzi, who reported on his results with
temperature drop testing on a 2013 Kia Optima, told us he
realized he was measuring from condenser inlet (compressor discharge line) to the liquid line at the condenser outlet.
On most new condensers that is also including temperature
drop across the sub-cool condenser or sub-cool section of the
condenser with its integrated receiver-dryer section (also
called the "modulator") Which adds another source of temperature drop to the condenser readings. But in most cases
you can't really get to condenser-only outlet tubing. So if
all you can do as a practical matter is get to the liquid line
following the sub-cool condenser section, well at least you
know why you're outside the rule-of-thumb. See FIG. 8.
But let's start at the beginning:
For many years we could count on the fixed displacement
compressor producing refrigerant temperatures in a certain
range. Although the temperatures in a particular system
might vary very slightly from one application to another,
depending on the length of the line from the compressor to

Figure 8: If the system (2008 Mazda6 shown) has a sub-cool condenser, it
usually is semi-combined with the main condenser. If so, it is impractical
to try to get condenser-only temperature drop readings. The readings, say
from condenser inlet to liquid line at the sub-cool outlet, reflect both heat
exchangers.

the condenser, the temperature peak would be comfortably
under 175 degrees F, and that still holds generally true. But
obviously, as the systems have been redesigned for higher
performance and efficiency with smaller refrigerant charges, the drop increased as the condenser flow passages took
a complex, multi-flow path with many really, really tiny
tubes. If the airflow available for condensing were similarly
reduced, we'd have a sort of balance and the temperature
drop might continue in the same range. And there are four
to five heat exchangers in the front-end module all competing for cooling airflow. But the condenser generally gets the
first, nearly-uninterrupted shot at it.
Further, the chance to improve condensing is irresistible
for an engineer -- nothing like a solid, cooler column of liquid
going into that expansion valve or orifice tube. Improved
condensing increases the temperature drop and A/C system
performance.

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