It depends on what kind of car you have. Late 124s have two fans; they should come on together. If one doesn't work, it or its wiring is bad. The 210s have two fans also but one is slaved to the other with a belt; if one doesn't work the belt may be broken, dislodged, or missing. Other models, I don't know.

BTW the switch in the receiver is a pressure switch, not a temperature switch, for turning on the fan(s) in low speed.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970