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Old 08-01-2014, 07:01 AM   #1
tmumolo
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AC Acceleration Question

Does anyone know if the AC on the MK3 has a shut off mechanism on hard acceleration? I live in an area where there are some two lane highways; when it's necessary to pass a slower vehicle or truck I almost always hit the AC button to turn off the air before I pass; idea being to get the most power to the drive wheels by turning off the AC compressor. Maybe it's confirmation bias but it does seem to make a difference. Is it my imagination?
I was just wondering if the cars computer has a built in way of doing this automatically.
Any thoughts?.


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Old 08-01-2014, 07:39 AM   #2
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The car does have the ability to disengage the AC, and alternator I believe, when the pedal is at WOT. I'm not sure if it's using an electromagnetic clutch or something else, my google-fu is weak this morning.
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Old 08-01-2014, 11:02 AM   #3
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Quote:
Originally Posted by tmumolo View Post
Does anyone know if the AC on the MK3 has a shut off mechanism on hard acceleration? I live in an area where there are some two lane highways; when it's necessary to pass a slower vehicle or truck I almost always hit the AC button to turn off the air before I pass; idea being to get the most power to the drive wheels by turning off the AC compressor. Maybe it's confirmation bias but it does seem to make a difference. Is it my imagination?
I was just wondering if the cars computer has a built in way of doing this automatically.
Any thoughts?.
I believe all vehicles have a WOT AC compressor clutch disengage.
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Old 08-01-2014, 02:44 PM   #4
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Quote:
Originally Posted by TooOld View Post
I believe all vehicles have a WOT AC compressor clutch disengage.
I appreciate the comments but I'm really interested in whether anyone actually "knows" rather than "believes" there is a WOT AC clutch disengagement on the MK3
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Old 08-01-2014, 03:28 PM   #5
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A/C Request

The HVAC control module uses a dedicated wire to send the A/C request message to the BCM. The BCM sends the A/C request through the High Speed Controller Area Network (HS-CAN) to the PCM .

When an A/C request is received by the PCM, the PCM engages the A/C clutch relay when:
• the refrigerant pressure isn't excessively high or low.
• the engine coolant temperature isn't excessively high.
• the ambient air temperature is above 6 C (43 F).
a WOT condition is not present.
• the evaporator discharge air temperature is above 7 C (45 F).

I assume these bullet points are "and" conditions meaning all must be true for the AC clutch relay to be energized, thus allowing current to the AC clutch coil.
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Old 08-01-2014, 10:18 PM   #6
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Quote:
Originally Posted by tmumolo View Post
I appreciate the comments but I'm really interested in whether anyone actually "knows" rather than "believes" there is a WOT AC clutch disengagement on the MK3
Yes, I have noticed it personally.
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Old 08-03-2014, 10:56 AM   #7
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Well, I don't have a definitive answer either, but next time, keep the A/C on and give it a good flooring. You will notice the air get hotter.
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Old 08-03-2014, 11:18 AM   #8
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Quote:
Originally Posted by tmumolo View Post
I appreciate the comments but I'm really interested in whether anyone actually "knows" rather than "believes" there is a WOT AC clutch disengagement on the MK3
Yes, we know there is a WOT cutout.
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Old 08-04-2014, 11:58 PM   #9
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Quote:
Originally Posted by tmumolo View Post
I appreciate the comments but I'm really interested in whether anyone actually "knows" rather than "believes" there is a WOT AC clutch disengagement on the MK3
As TooOld mentioned, a WOT A/C cutoff is pretty much universal in any modern car.
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Old 08-05-2014, 12:00 AM   #10
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As TooOld mentioned, a WOT A/C cutoff is pretty much universal in any modern car.
Look out, "pretty much" isn't good enough for this guy who won't just Google it! LOL!
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