The fan clutch can fail in a few ways. One is that the fan can lock up. If so, it will make some noise like an airplane ready to take off. The other way is to freewheel. This will cause the car to run hot.
IF yours is not heating well, try a hotter thermostat. Be sure the mono-heat valve and the auxillary water pump is working...The mono-valve is cheap and they fail alot with no/little heat complaints.
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM
[This message has been edited by Benzmac (edited 01-15-2000).]