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Old 05-29-2012, 04:25 PM   #1
Smurftastic
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Default A/C Compressor randomly engaging when turned on - freon overfilled?

I finally replaced a broken A/C. tensioner bolt and plugged in a new A/C compressor (45K miles). The freon is full.

The problem I am now having -- while turned on, the A/C compressor randomly engages. Engagement is not consistent, but while the compressor is engaged, the A/C is quite cold. I do not believe the compressor has any issues, because it's not emanating any noises associated with a broken clutch or worn out bearings. The system is also not freezing.

My only diagnosis thus far is that the freon could be TOO full, which according to basic NASIOC research can lead to this problem. So, time to grab a PSI gauge and measure.

NASIOC braintrust - any other ideas before I tackle this?
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Old 05-29-2012, 05:19 PM   #2
Jessekrs123
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It's completely normal for the compressor to engage and disengage while being operated. It should cycle regularly if it is functioning properly.

As long as it is not flickering or engaging and disengaging rapidly, which would indicate too much pressure in the system. If not then you probably don't have a problem.
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Old 05-29-2012, 05:23 PM   #3
anthonywrx
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is it engaging while your front defogger / defroster is on? Remember that your A/C condenser WILL kick on while that mode is selected to draw moisture OUT of the cabin.


just a simple heads up just in case
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Old 05-30-2012, 07:15 AM   #4
Smurftastic
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I anticipate the system will engage and disengage while being operating, and believe (rightly or wrongly) that this fluctuations based at least partially on engine load. However, my frustration is the compressor isn't engaging long enough to keep temps cool in the vehicle. I'll be driving along and it's working fine, then disengages.. and it'll get hot in the car. A few minutes later the compressor engages again and it gets cool. At the end of the day, the compressor seems to have a mind of its own
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Old 05-30-2012, 08:22 AM   #5
lolol
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Did you evacuate the system after you opened it? Air is non-condensable and it will cause the pressure to overshoot if left in.

If you didn't pull a vacuum, then you should recover the charge, evacuate and recharge.

How much refrigerant does the system call for and how much did you put in?
Charging by weight gives the best result if you have the patience to do it right.
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Old 05-30-2012, 08:49 AM   #6
NitroTrike
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A good starting point is to use the "real" gauges that tell you both low and high side and check the static pressures (engine not running). Let everything cool down for a few hours (meaning don't drive 500 miles and check it - the underhood temps will throw off the readings). The static pressure on both gauges should be close to the ambient air temperature.

As someone else stated, it's completely normal for it to cycle - it's when it doesn't cycle and continuously runs that indicates a problem.

Now when it's running... These numbers are by no means "carved in stone" but it's a good starting point, so if you notice a 10% +/- don't get all gung ho and pump more into it.


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Old 06-21-2012, 08:55 PM   #7
Smurftastic
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Turned out the shop that put in freon overfilled it. Once the engine got hot enough to build pressure in the AC lines the compressor would shut down to avoid damage.

My low side pressure at operating temperature was more than 300 PSI at 100ish degrees.

Wow.

Fixed now
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