Could you elaborate more on the variable pressure system? I'm pretty familiar with commercial a/c systems and somewhat familiar with auto a/c systems. I know that sanden is now selling scroll compressors for automotive use, but I've never heard of variable pressure before.
We are designing a bigger (15 ton), constant run a/c system at work that uses copeland scroll compressors, a Sporlan electronic discharge bypass valve, and a head pressure control valve. We needed all of this hardware so the system would run reliably at low and high ambient outside conditions.
We wanted lieberts variable displacement compressors which have a valve release in each cylinder to cut them in and out as needed. These were too noisy for our application, however.
I also am aware that MB has traditionally used thermo expansion valves instead of orifice tubes like most domestic manufacturers. This expands the freon at the maximum allowable flow rate without sending liquid back to the compressor. On a domestic a/c system, you need a suction side accumulator to store the liquid freon that passes the evaporator so it doesn't damage the compressor.
That being said, I own two MB's converted to R134 and neither cools worth a poop. Granted one is 20 yrs old and the other 30, but my impression is that MB's climate control systems are not up to domestic standards.
What else, '73 MB 280 SEL (Lt Blue)
Daily driver: '84 190D 2.2 5 spd.