The high and low are affected by ambient.

I almost exclusively work on AC when it's "Africa hot out" and on my e53 with not variable compressor, I typically see about 45/250 at 90f=32c ambient. I wouldn't go much higher, there are diminishing returns it will actually cool less well when too much charge.

250/45=5.556
275/50=5.5

The difference between high and low is directly related to how much heat can be transferred.

(It's why it works better when low on freon but will freeze up the evaporator).

175/35=5
230/30=7.667

5.5 works fantastic without freezing the evaporator, 6.5 will freeze there evaporator for sure.

5.0 likely a little weak

The numbers both go up when ambient is higher; it's likely that the ratio almost cancels out the ambient temperature and you could charge using the ratio no matter the temp.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)