: cooling fan relays

10-02-13, 10:43 AM
hello Everyone,
the eldo overheated twice, I don't believe its a HG problem. The cooling fans did not come on when they should have. I did not notice that the first day. I added water not Dex and watched coolant carefully. Second time (next day) it overheated again, probably because of the water instead of Dex also the rad cap was old. this morning I put in dex and a new cap we will see. Here is my statement, the fans work on AC so they are good, they do not which of the three relays control the hot coolant fan on . the owners manual indicates 1 AND 3 are powered by the same fuse (alldata says the same).Can you unplug the sensor in the head and jump the end or check the relay? Which one is it left-center- right? One would believe the center is #2, if I change it do I have to wait until its at running temp to see if that was the problem?
Thanks for the help. gotta go to work now
10/02 9:45am

10-02-13, 11:48 AM
Water vs Dex has no affect. Water will cool as good or better than coolant.

This is for 2000+ so I'm not sure if it is the same, but I suspect it is.

Courtesy of Submariner409

10-02-13, 12:28 PM
thank you for your reply. Is there a way to check the relay or the sensor? Do you think the center relay controls the (overheat) function? Can I jump the connector pins on the temp sensor in the head to check the system?
I put in the Dex because it has a higher boiling point, I didn't want to until I fixed the problem, but I was trying to give the N* its best chance, hopefully the rad cap fixed it!
thanks again for your response. Ed

10-02-13, 03:35 PM
I'm not sure how to check the sensor or relay. I'm sure there is a procedure in the FSM.

10-02-13, 04:43 PM
Fans run in SLOW any time some A/C compressor function is called for OR when coolant hits 224 degrees. Fans go to FAST at 236 degrees coolant. The S-P relay controls SLOW-FAST speeds. In SLOW the two fans are set to series operation: The circuit voltage drop runs them at 6.5 to 8.5 volts, depending on system voltage. FAST has each fan powered by total system voltage. Follow the voltage paths in the circuit diagram.

To check a relay, pull it out (TIGHT !) and look at the circuit diagram printed on the side. If you apply 10 - 12 volts across the solenoid pins it should click. A continuity check across the power pins should show open when the relay is OFF, continuity when SHUT (ON). The pin circuits are also shown on the diagram posted earlier.

The S-P relay is a 5-pin, so you'll see differing continuity across the 3 ON/OFF pins.

The 4-pin relays can plug in in any orientation - the circuit pins are diagonally connected. The 5-pin will only plug in one way.

A handful of double-ended alligator clip test leads and a half-decent VOM from Radio Shack will do for test gear, along with a 9-volt alkaline battery.

The ECT sensor is a variable resistor - it will change value as it heats up due to coolant temp change. Test it by using a sauce pan of water, the ECT hooked to test leads (2 pins), suspended in the water - resistance change as the water heats on the stove. You can test a thermostat in the same saucepan, using a candy thermometer to see where it starts (188 degrees) and is fully open (206 degrees).