The high pressure line is also called the liquid line. It contains HOT liquid. Touch the high-side line when the system's running and you will understand why. Now think about the effect of HOT liquid being shot into the suction line at 250 psi just a few inches from the running compressor. Your reed valves will turn to shrapnel. That's why I referenced the expansion valve. The refrigerant cools as it expands past the expansion valve and evaporates inside the evaporator.

Ideally you would want to pull a vacuum on one system and hook up high-side to high-side, low-side to low-side, and allow the evaporation process to move the refrigerant, along with maybe a little heat (systems not running). But like I said, I can't think of any device or hose configuration in existence that would allow you to do that...

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280