Shall we assume you're asking about the 96 E300? Near the brake master cylinder sounds like the high side, low side more likely to down by the radiator. What color cap is the one you see?

High side will be in line from drier to condenser, up by radiator..I think is is actually in front of radiator on that chassis...low side is by brake master

It's the other way around Low Side on Top and High Side on bottom by the grill!

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William
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1987 420 SEL - Like a fine wine only better with age

high side is behind the fan grill, under a little plastic cover on drivers side

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1967 250 S
1967 280SE
1968 250S
1971 280 SE
1973 220
1974 280 S
1975 450 SEL
1976 220 D
1979 300SD
1983 300 SD
1985 230 TE euro
1986 280SL
1986 500 SEL euro
1986 190E 2.3
1990 300 SE
2003 C230 K
2004 C230 K
1987 560SEL
1987 300SDL now in canada
2005 C230
1998 C43 AMG Sold to DON
1993 190E 2.6
300TD Former daily driver Totaled
current:
R320 CDI
Ram 2500 Cummins