there's a number of things that can cause this. one is a restriction downstream from the high pressure switch or a bad switch. The pressure goes up until the switch is opened, which causes the compressor to cut out, which causes the pressure to drop, which causes the pressure switch to make, which causes the compresor to engage again, which increases the pressure until the switch opens, etc, over and over.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.