MACS Service Reports - 2015 - FEB4

A/C PERFORMANCE ISSUE
you know the story.
The solenoid was described in factory service information
and supposedly was covered for diagnosis by the DRB III scan
tool, but probably not.
More often there are "phantom" systems that are covered in
shop manuals that never get into production. We remember a
two-stage front-end belt accessory drive for Mustang many
years ago. It was intended to be a fuel economy enhancer, by reducing the power draw of the accessories. Ford fully developed
it, and there it was, described in full detail in the shop manual.
But it was expensive and therefore dropped from production
before the first models rolled off the assembly line. ■

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The part exists, sort of. The 2001 Dodge Caravan minivan
with Automatic Temperature Control had poor rear A/C cooling performance and the technician decides (correctly) the issue
is with the rear expansion valve. But it's not like one with which
he's familiar. It has a solenoid on it (Figure 5). He tries to get a
replacement, but the one the dealer has is not the same. It has no
solenoid. But the dealer insists it's the correct replacement and so
he decides to try it. He just folds back and tapes over the wiring
from the harness and installs the new expansion valve. The rear
system works fine and the minivan is out the door.
We occasionally see these "different" parts and if you're wondering, "What gives?" we'll talk about this one as an example. The
solenoid comes with a two-wire pigtail, with one wire that was
hot-wired into battery current at the rear blower motor relay on
a fused output circuit, and the second wire was connected to the
ATC control head, to a terminal that would provide the ground.
The ATC control head was supposed to be programmed so that
with the rear A/C turned off, the solenoid would shut, blocking
refrigerant flow to the rear evaporator. This would improve refrigerant circulation through the front system for better cooling
performance.
Sounds like a good idea, but later testing indicated that oil
might be trapped in the rear system, affecting lubrication of the
compressor and shortening its life. In any case, a lot of those
solenoid-equipped expansion valves were installed, but the
decision was made to cancel the project, and the control head
was never reprogrammed to operate the solenoid. But Chrysler
apparently had a supply contract for those solenoid-equipped
valves, and so it used them in production. But without the reprogramming, they didn't work. Is it possible that some early
ones were programmed? Not that we heard, but it doesn't really
matter. Other upgrades to the system produced acceptable performance and if you ever see that valve on a 2001 model, at least

Figure 5: Rear expansion valve solenoid was intended to shut off refrigerant flow to rear HVAC on 2001 Dodge Caravan, but computer was never
programmed to operate it. So replacement TXV has no solenoid.

IT'S NORMAL. IT REALLY, REALLY IS (MUCH OF THE TIME ANYWAY)
The 2005 Toyota Tacoma 4.0 V6 was a recent used vehicle
purchase, and the relatively new owner had a simple complaint:
when he turned the system to floor-only heat, he noticed that
some of the airflow went to the defrost outlets. Other mode selections produced the normal, precise response, but it seemed to
him (and the shop to whom he brought the car) that the mode
selector was malfunctioning. The technician pulled the mode
actuator, manually operated the doors and they seemed to be
operating smoothly and he could see nothing wrong. He was
leaning toward installing a new plenum assembly, on the assumption that there was warpage or misalignment. Fortunately,
he was able to check with other technicians with Toyota-specific
experience. The answer he got: there's always some bleed to defrost in floor mode. This small amount of continuous defrost is
there so the driver doesn't have to switch to defrost repeatedly to
clean windshield fogging.

February 2015

Interestingly, every Toyota product we've driven in cold
weather also has the bleed to defrost in floor heat mode. In fact,
lots of vehicles do. We suspect that a new owner of a used car
is looking for things that might be wrong, more so than with a
brand-new vehicle.
Here's another example of a used vehicle purchase. A 2007
Honda Odyssey owner complains that there's very little heated
airflow from the floor registers in the floor heat mode, and there
is some heated airflow bleed from the dashboard side registers.
The technician finds there are shut-offs for these side registers
and when he closes them completely, the heating from the floor
registers is much better. However, the logical question: is something wrong that forces the driver to close those registers, eliminating the small amount of heat at midpoint that flows from
them? The technician suspects a misaligned mode actuator or
some defect with the HVAC case. But once again, a check with

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Table of Contents for the Digital Edition of MACS Service Reports - 2015