MACS Service Reports - 2016 - SEP7

ANOTHER INTERMITTENT A/C - THIS TIME HYUNDAI

September 2016

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Triple pressure switch
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In-car sensor
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Photo sensor
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Water temperature sensor
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Ambient sensor
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Air Quality Sensor(AQS)
The now-desperate technician connected his oscilloscope to
the "water temperature sensor" and PCM and just watched as
the system ran and then stopped. Just before it stopped (breaking the A/C relay ground), the "water temperature sensor" started spiking. A new sensor was the durable fix. ■

Hmaservice.com (hyundai)

This one doesn't absolutely seem to have to be a bad connection. The car is a 2008 model (Hyundai Tiberon) and after running for some time, it stops. But then, after a while it starts by
itself. So maybe there's a temperature or pressure issue. While
it's running, the technician checks the pressures and they're normal. Ditto for when it restarts. Engine coolant temperature also
is normal, from the start, through the system failure, and the byitself restart.
At this point the technician starts throwing parts in. First, he
changes the evaporator temperature sensor. System seems to
work for a couple of days, but then it's back. Next he changes
the expansion valve and the control head - same result; system
works for a couple of days and then is back.
When the system shuts off the next time, the technician suspects a borderline large gap in the compressor clutch, but no,
it's okay. He then looks to confirm that the problem is electrical by checking for a ground from the powertrain computer. No
ground, so he replaces the computer, and once more the system
works for a couple of days.
The answer is that something is causing the powertrain computer to disconnect the A/C clutch circuit.
The wiring diagram (Fig. 8) shows a pretty standard Asian circuit, with an A/C control module with an A/C select (request)
signal wire to the PCM, and the "biggie," the triple pressure
switch, which is wired from the A/C on terminal of the control
module to two terminals on the PCM, one for low and high
pressures, the other for medium pressure readings. The triple
pressure switch provides the signals for the radiator electric fans
and logic for the PCM control of the A/C relay, so it's an important part to check. The fans were operating normally with
the A/C too, but we apparently have a slow-acting intermittent,
although the connections at the switch, the A/C control module
and the PCM pass a wiggle test. In fact, he wiggle tests just about
everything else in the circuitry, the relay, the connections at the
compressor (particularly the ground), the control module and -
wait, almost forgot the evaporator temperature sensor, but that
was next.
At this point, he replaces the relay, just because he can, but of
course the problem remains. Should he change the A/C control
module next? No, because that would not cause the PCM to drop
the ground.
What's left? The wiring diagram for A/C is missing the answer
but the table of contents for the air conditioning system has it: "water
temperature sensor" (coolant temperature sensor, of course).
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Air conditioning System
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General Safety Information and Caution
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Description and Operation
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Repair procedures
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Compressor
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Condenser
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Condenser fan & relay
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Receiver-Drier
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Refrigerant line

Figure 8: This 2008 Hyundai Tiberon HVAC circuit is typical of Asian
design, with the triple pressure switch providing inputs to the powertrain computer, both for three pressure ranges to set fan speeds and
high-pressure cutout. So a switch failure is a common cause of A/C cutout -- but not in this case.

MACS Service Reports

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Table of Contents for the Digital Edition of MACS Service Reports - 2016