Tuesday am -

OK - found the little bugger. Right behind the alternator.

[ locating various parts on my Benzes is a continuing challenge
to this diy'er. ]

Of course this morning it's only 70 degrees, and started to rain on me as soon as I connected up the gauges. AC may not even be kicking on; in any event, low side about 30 psi, hi side very low, about 10. I would think either the compressor is not even on (likely if the ac isn't even kicked on by climate control!) or I have a compressor malfunction. Though the diagnostics section of the Mastercool manual suggests hi side pressures of about 121 psi in this event.:confused