Seville V8-300 4.9L (1991)
Radiator Cooling Fan Motor: Description and Operation
Circuit Operation
The ECM controls both coolant fans by controlling three relays through two outputs. There are two modes of coolant fan operation. One mode is the
series mode where only coolant fan relay B is energized by the ECM and both coolant fans run at low speed. The second mode is parallel mode where all
three of the coolant fan relays are energized by the ECM and both coolant fans run at high speed. Coolant fan operation is only possible when the
ignition switch is in the RUN position.
The coolant fans will run at slow speed when circuit 535 is grounded by the ECM at terminal 2A11. Coolant fan relay B is energized and voltage is
applied to both coolant fans.
The coolant fans run at high speed when circuits 535 and 536 are grounded by the ECM. Grounding circuit 535 energizes coolant fan relay B and
battery voltage is applied to the pusher fan. When circuit 536 is grounded coolant fan relays C and D are energized. Coolant fan relay C provides a
ground for the pusher fan through circuit 804. Battery voltage is applied through coolant fan relay D to the puller fan.
Series Mode
The BCM will request the ECM to turn On the coolant fans at low speed when A/C high side temperature is greater than 140°F and will request the
ECM to turn the coolant fans Off when A/C high side temperature drops below 122°F.
The BCM will also request the ECM to turn the coolant fans On at lo speed when vehicle speed is less than 20 mph, A/C compressor clutch
engagement is possible or the outside air temperature is greater than 113°F.
The ECM will turn On the coolant fans at low speed when coolant temperature is greater than 212°F and turn the coolant fans Off when coolant
temperature falls below 208°F.
Parallel Mode
The BCM will request the ECM to turn the coolant fans On at high speed when A/C high side temperature is above 158°F or an A/C high side
temperature sensor failure is current and A/C clutch engagement is possible. The BCM will request the ECM to turn the coolant fans Off when A/C high
side temperature drops below 138°F.
The ECM will turn the coolant fans On at high speed if coolant temperature is above 226°F or a coolant temperature sensor failure is current. The
ECM will switch the coolant fans Off when coolant temperature drops below 222°F.
