Fans are wired in parallel, so both run at the same time, unless one of them has a problem. Sounds like that's what you have nucor. It's either the wire/connector to the inop fan or the fan motor itself. If you've already tried spinning or tapping the fan to free it up and it still won't work, it's likely a bad motor. Each fan has a plug-type connector. Check it for continuity.

__________________
1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't