Q: My AC has been coming and going. on 2009 Saturn Outlook

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I bought AC Pro to install, but the gauge wouldn't get out of the red. The Youtube instructions said that it needs refridgerant if it does this. The air is actually working at the moment though. Can I install refridgerant myself and if so, where do I? I had a heck of a time locating the low pressure line deep in the belly of this beast!
(1) Answer
Yes, you can. Locate the valve on the low pressure line and remove the plastic cap. Turn on car and set ac function and fan blower to maximum setting. Attach refridgerant to the valve and observe gauge. Hold can in upright position and shake well as you squeeze trigger to allow to flow into line. Periodically, release trigger and observe the new pressure reading on the gauge till it is in the required operating zone. The zone is set by turning the gauge to the ambient air temp (outdoor temp.) to the center of the red lines. Any reading in this range that holds stable is good for operation.