Pull the wire off the sensor and ground it to the engine (usually on the thermostat housing on a 617). Fan must run. If not, check:
Replace fan fuse (25A) and verify current at the fuse. These often corrode, assume it's bad. Check connections at the low speed resistor. Repair if corroded. Pull sensor wire at thermostat housing and ground with ignition on, fan must run. If not, verify relay operation, replace if defective. You can jump the connection at the relay socket to test fan. If you get current flow (spark, hot wire) but no fan, it's bad. Check the connection at the fan as well, they sometimes get dirty or corroded as well. You can apply voltage from a spare battery directly to the fan wires at this connection to test it as well. Peter -----Original Message----- >From: andrew strasfogel <astrasfo...@gmail.com> >Sent: May 5, 2010 12:21 PM >To: Mercedes Discussion List <mercedes@okiebenz.com> >Subject: [MBZ] Testing procedure for a nonfunctioning W123 aux. cooling fan > >My 1983 300TD ran hot last weekend because the auxiliary cooling fan wasn't >coming on. Could someone please tell me (step by step) how to bypass the >temp sensor switch in order to test whether the fan itself is defunct, or if >I have a different problem? If I need a new aux. fan is there a difference >in the brands? TIA, > >Andrew >'83 and '85 W123 300Tds >_______________________________________ >http://www.okiebenz.com >For new and used parts go to www.okiebenz.com >To search list archives http://www.okiebenz.com/archive/ > >To Unsubscribe or change delivery options go to: >http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com _______________________________________ http://www.okiebenz.com For new and used parts go to www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
