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With the engine running, connect the gauge to the low-pressure port on the A/C system. The high side has a larger adapter, so you can’t accidentally attach the gauge to the wrong port. With the gauge attached, you can now turn the valve to add more refrigerant to the system. In the photo inset, you can see the pressure for this A/C system is exactly where it should be”in the middle of the white range. Remember to use heavy-duty leather gloves and eye protection when working around A/C components. It’s possible that a fitting or a valve may break or otherwise leak refrigerant on your hands.
A belt that runs off the main crankshaft operates the A/C compressor. On cars with a manual adjustment, make sure you don’t tighten this belt too tightly, or you may place undue pressure on the bearings inside the compressor. If you suspect you might be having problems with the compressor, check the belt first. Turn on the system, and verify that the electromagnetic clutch is engaging. If it is not, you may need to replace it. Check the power connection to make sure it is live before replacing the clutch.