Posted by Wally Plumley Wally Plumley
on 6/26/2007, 4:50 pm, in reply to "87 S4 Neither Cooling Fan's Are Running - Help!!!"
74.224.149.85
1) Does the A/C work? If so, do the fans run when you turn the A/C on?
2) Was the engine actually overheating? It is not unusual for the temp gauge to lie to you.
3) The fans turn off when you open the hood - check whether they are running without opening the hood.
4) The fans are turned on by:
- Coolant temp sensor, located on the lower forward face of the left radiator tank. Shorting the harness plug for this sensor with the ignition switch on and the hood closed should turn both fans on.
- A/C freon pressure sensor, located on the receiver/dryer. Same test.
- Torque converter temp switch (autos only) located on the torque converter housing. Same test.
- Intake manifold temp sensor, located on the top of the intake plenum. This is the only sensor that should turn the fans on with the ignition switch off. Test by shorting the two connectors.
5) Relay XVIII controls the flaps. Both the flaps and the fans are controlled by the Cooling Fan and Flap Unit, loacated in the passenger door sill area. The fans are operated by the Coolant Fan Amplifier, located on the front valance panel.
6) There are two fuses for the fans - #28 & #29. Check for power on the red wire and the red/white wire at the amplifier.
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