MACS Monthly Newsletter - 2020 - FEB3

airsept.com

ing anymore (if indeed he ever did), he may decide to
save money and go for the "cheap fix."
But should he? There's always less A/C cooling from a
rear system (as we have noted in the past), and if it's 10°F
higher outlet temperature (maybe even a bit more, say,
15°F) in really hot weather, that can be considered "near"
normal. The rear system just doesn't have the capacity of
the front and on an older, high-mileage vehicle, there has
to be a level of acceptance, unless there's a small leak that
might not be that difficult to find and repair.
As we've noted in the past, a common source of rear
A/C leakage is from the long refrigerant lines that go
from under the hood and then under the body to the
rear HVAC unit, typically mounted behind a large trim
panel in a rear quarter panel. Those long lines are, for
most of their route from front to rear, exposed and subject to damage from corrosive road film, and impact from
abrasive solid road debris. You should be able to find the
source of a leak with an infrared electronic leak detector. Obtaining and replacing the lines is a major project,
but with a small leak, a simpler fix can be made with a
line splice, such as a swage type (if you stock that type,
from American Lokring-lokring.com) or the compression fitting type, such as the AirSept type-airsept.com,
supplied in 45° and 90° designs along with straight connectors. See Figure 4.
But what if there's no leak? That's when many shops
just give up on an older model and "sell" the installation
of block-off fittings. A common line is that, "it seems to
be in the rear HVAC case, and we can't get repair parts
for those, so..."
Well, it might be in the rear case, but more than likely it
isn't. You could remove the trim panel and get to the flap
doors and actuators, and that's a lot easier than working

Figure 4: These three compression-type repair fittings are especially good for repairing small leaks in the lines to the rear HVAC
system.
from under some dashboards on the front system. But
before you go that far, let's look at this case from a 2014
Chevy Traverse, an SUV with poor rear cooling and no
guidance from trouble codes.
Ah yes, the dreaded no code diagnosis issue. Actually,
many shops prefer that because it often means the problem is non-electrical/electronic. When a rear HVAC fails
to cool properly, and the enabling controls seem to be
working, too many technicians ignore a simple test they
would "automatically" do for a front system: clamp off
the hoses to the rear heater core. A technician who performed this test on a full-size SUV with rear HVAC found
that the rear outlet temperature dropped to just over 50°F
(front registers were producing 40°F air).
He took the "keep it simple" approach. Instead of trying to rework rear HVAC case flap doors on an older vehicle where the owner had a limited budget, he just installed a manual shutoff valve in the inlet hose to the rear
heater. It's closed during much of the year and opened
for winter. n

A TOUGH DECISION?

February 2020

techinfo.toyota.com

The car is a 2009 Toyota Corolla and we don't have a lot
of detail on it, although it's the subject of a YouTube video you can watch if you choose. Straightforward issue:
no cooling and a pressure test shows equal (ambient temperature related) pressure on both sides of the system.
Obviously, the compressor isn't pumping, and because
it's a piston compressor with a displacement-control solenoid, the diagnosis is either the solenoid or a mechanical issue resulting in no change of displacement. There is
no clutch in this compressor design, although you may
find Corolla compressors of this vintage with a clutch.
The technician quickly determines that although the
belt-driven pulley is spinning, the plate in front of it,
which is attached to the compressor shaft, is not. The
connection is made by a plastic "damper limiter," part
of which (combined with the pulley) is called a "breakaway" hub assembly. If the spokes of the limiter break,
the pulley alone will turn while the outer plate of the

Figure 5: The pulley, made of plastic, has six rubber dampers
to absorb engine torque fluctuations and spokes that form the
pulley structure. If the compressor seizes, the spokes break to
separate the pulley from the compressor shaft plate, but the
belt still can turn the pulley so other belt-driven accessories
will continue to function.

MACS Service Reports

http://www.airsept.com http://www.Lokring-lokring.com http://lokring.com http://www.type-airsept.com http://airsept.com http://techinfo.toyota.com

MACS Monthly Newsletter - 2020

Table of Contents for the Digital Edition of MACS Monthly Newsletter - 2020