My 84 300SD acts the same way. It's a dog starting off with the A/C on. Throw in a road incline and it's almost unbearable. It's times like that where I temporarily turn off my A/C until I get up to speed. I also turn it off when I pass slower folks on the two lane country roads around here.

I guess you would say the A/C Off button is a "boost" button.

.....Dan

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99 e300
98 e300
90 Suburban 1500 4x4
92 ZR-1
04 Tahoe 4x4
05 Scag 52" zero turn
97 e300 - totaled on black ice
84 300SD - gave to a friend
85 300TDT Euro - SOLD to my little bro