Okay, I thought that you would loosen the belt, engage the clutch and then spin the pulley by hand. I don't know much about AC systems. Is the clutch suspended in the center of the pulley when not activated, and then magnetically attached to the pulley when engaged?

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'81 300SD

Yes, the face of the clutch is pulled towards the pulley making contact and driving the compressor.

As for recharge, the R12 cans don't seal very well once punctured so I'd tend to use full cans only then have it topped off at the shop. R132 cans have a screw on top making them less leak prone.

I was planning on emptying all three of my cans of R12 into the system, but according to vstech, the system needs to get started with weighed liquid R12 first.

I also just saw that my Egelhof expansion valve has R 134a printed on it. I'm hoping that this means the valve is compatible with R134a, but not solely for use with it.

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'81 300SD

Not an AC expert, but it you are keeping the system R-12, this doesn't sound right to me. Two different gasses with different pressure curves, I doubt a TX valve is made that is designed for both. However, the MB factory guide for replacing R-12 with R-134 does not require replacing the TX valve, so go figure.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC