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Old 04-29-2015, 08:52 PM
jay_bob jay_bob is offline
Control Freak
 
Join Date: Oct 2011
Location: Columbia, SC
Posts: 2,925
On the 87 124s the auxiliary fan is controlled by the two sensors directly. (88 and up they changed the control of the high speed to the PBU)

Low speed power path: fuse D -> relay K10 -> resistor -> fan motor
High speed power path: fuse D -> relay K9 -> fan motor

Low speed control path: fuse 7 -> relay K10 coil -> S32 (refrigerant pressure sw at dryer, directly behind the left headlight) -> ground

High speed control path: fuse 7 -> relay K9 coil -> S25/5 X1 pin 2 (this is the 3 pin sensor switch on the water neck on top of the head just to the left of the fuel filter - pin 2 of the 2 pin connection, ground is pin 1 of the 2 pin connection) -> ground

If you short the leads at the pressure switch, K10 should pick up and you should get low speed.

If you short the leads on the 2 pin connector at the temperature switch K9 should pick up and you should get high speed.
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2014 ML350 Bluetec (wife's DD)
2008 ML320 CDI (Kids college DD)
1998 E300DT (my DD)
1987 300TD (eternal project, I'm in too deep to quit now)
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gone but living on
1983 240D (body to greazzer, engine to t walgamuth)
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