Well Timmy's 93 model is a car that came from the factory with 134, so I'm not sure about the sight glass being useless. On a converted car, it is indeed useless. Even on an R12 car it is an indication but not a conclusive indicator.

Timmy, you need to get us pressures and temeperatures. Connect manifold gauges, stert car with a/c full on, set engine speed to 1500 or a little more, give it five minutes to stabilize and right down pressures, ambient temp and vent temp. That will tell the story.

Also while doing this it is best done with a high volume fan placed in front of the condensor.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

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