MACS Monthly Newsletter - 2017 - AUG6

airsept.com

(as does one competitor). When you unplug the solenoid connector, you connect from one of a set of harness adapters to the
EVC-1, and then plug the solenoid (via another harness adapter) to the tester. Because the circuit (even with just the pin connections) is now electrically straight through (from the HVAC
computer module to the tester to the solenoid), a trouble code
will not be logged when the compressor is run for testing. One
earlier tester requires connecting a "fooler module" to the computer harness to avoid a trouble code (it fools the HVAC control
module into believing the system is connected normally).
The EVC-1 display screen varies according to the model chosen. In the illustration (Figure 12), there's just one temperature
scale (32°-74°F) that clips onto the low-side line or goes into the
A/C register. But there are ESV-1 models with two plug-ins for
temperature scales (the second for 100°-200°F), for high and low
side refrigerant lines, and those have wire leads that clip to both.
If the temperature(s) don't respond to changes in duty cycle, the
problem is with the solenoid valve or compressor. If they do respond appropriately, the solenoid and compressor are good and
there's an issue with the HVAC control system or a refrigeration/mechanical issue.
Of course, a technician also can hook up his pressure gauge
set and watch the readings as the testing changes the duty cycle
command, for which there's another scale on the display. But the
design of this tool is to save the technician the need to hook up
pressure gauges.
As we've noted, there are now at least three of these testers on
the market, and we've now covered all three. You should have
one on your tool board. ■

Figure 12: AirSept EVC-1 is newest duty cycle tester for solenoid valve
compressors. It's initially available with a single temperature reading and
clip-on lead, but by Fall will be available with two temperature leads and
harness adapter kits instead of the "universal" connectors for the vehicle
harness and solenoid.

MAYBE, BUT MAYBE NOT
happens, the problem "seemed" to go away. But it
came back in short order and so the next step was
to check that No. 203, inconveniently buried under
the upper left side of the dashboard. Again, no luck.
It was clean and tight, as you could expect from the
well-positioned, clean and dry location.
Time for a tapping/twisting/grabbing test. We
know technicians who believe that the best diagnostics are tapping modules, turning switches on
and off, grabbing and moving harnesses and looking for a response. The technician noted that turning the HVAC mode control to floor/defrost would
put the system into recirc, and with the HVAC off,
the recirc light (and occasionally the A/C light)
would go on for an instant. That seemed to point
to the control head, and tapping the control head
at the fan control switch would get the fan to start,
and keep running as long as the tapping and pressure were maintained. Take away the tapping, and
the blower eventually would stop. That seemed to
point to the control head, and indeed a new control
head was the durable fix. ■

The 2007 Ford Edge with the 3.5-liter V6 and a
"simple" manual air conditioning system had what
seemed to be a rare problem but with a strong indicator for a troubleshooting clue: when the driver hit
the brakes hard, the air conditioning would come
on. Obviously an electrical problem, and maybe a
bad connection. Was there a weak engine mounting problem, so the engine shifting caused a short
of some kind? Or maybe there was a weak ground
that was shared by the Anti-Lock Braking/Traction
Control system and the HVAC. Any trouble codes
to provide the start of a road map? Sorry, but no.
The engine mounts seemed to be in good condition, and so the technician checked the wiring
diagram, which showed that the HVAC and the
anti-lock brakes shared the same ground: No. 203
(Figures 13A & 13B). Aha, there must be a bad
ground.
Not so fast. The underhood did show a lot of corrosion at the battery cable connections and there's
an unwritten rule that says to fix the obvious problems first. Inasmuch as you can't ignore badly corroded terminals, simple logic says clean and tighten those first. So the technician did, and as often

August 2017

MACS Service Reports

http://www.airsept.com

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