Originally Posted by gsxr

Tom, if the high-speed fan switch (the three-prong, 105/120C switch) is old or original, yes I'd replace it. Part number is 006-545-61-24, about $25 or so, this is the recommended switch for all 1986-87 OM603 turbos.

If you have a "green" refrigerant pressure switch that is working OK, it should be replaced with the new "red" switch the next time the AC system is evacuated for service. Otherwise, it's probably not worth the hassle to discharge & recharge the system just to change the switch - unless it's bad, of course. The newer red switch will trigger about 60psi lower, making the fan run more often, improving AC performance a little bit at idle speeds. The switch is cheap but AC service isn't...

From memory, the green switch turns the fan on at 20 bar and off at 16 bar. The red switch turns the fan on at 16 bar and off at 12 bar. HUGE difference there. And not to sidetrack this thread, but if your car still has R-12, pay whatever it takes to KEEP it R-12. The R-134a conversion is the kiss of death to any original R-12 system, and I know more than one person who converted back (at great expense) due to the inferior cooling with the R-134a.