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Old 07-16-2010, 07:43 PM
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Electrical Fans testing? Still not coming on

hi guys,

i still haven't had any luck getting my dual fan setup to work in my 1984 jag xj6 conversion powered by a 1996 impala LT1.

is there a way to test and see if the harness is bad? the relays are OK, and the fans themselves work when voltage is applied. The temp of the car shot up to 260, and the fans didn't come on (either fan).

I'm not sure what else to do... someone suggested putting a switch inline, could you give me a little more info about this?

Since i have OBDII i can't seem to mess with the settings of the fans coming on either, at least through the ALDL connector and CATS. Argh!

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Old 07-16-2010, 08:27 PM
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Quote:
Originally Posted by tylerwerrin
hi guys,

i still haven't had any luck getting my dual fan setup to work in my 1984 jag xj6 conversion powered by a 1996 impala LT1.

is there a way to test and see if the harness is bad? the relays are OK, and the fans themselves work when voltage is applied. The temp of the car shot up to 260, and the fans didn't come on (either fan).

I'm not sure what else to do... someone suggested putting a switch inline, could you give me a little more info about this?

Since i have OBDII i can't seem to mess with the settings of the fans coming on either, at least through the ALDL connector and CATS. Argh!
You say the "relays are OK".

Does that mean that the thermostat or temp switch is able to switch the relay "on", and that power then leaves the relay heading to the fan- yet the fan will not work?

If that IS the case, look for a bad ground circuit. Or an open in the power to the fan.
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Old 07-17-2010, 10:38 AM
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How do you know the relays are good? there are two functions to a relay. Switching voltage on and off to the fan, is one the other is responding to a signal, arriving from the control or temp sensor causing the relay contacts to close and turn the fans on and off .. You have looked for a fuse right.. and checked that..

I am assuming that this is not under computer control however even at that, basically the temp control and fans off and on are the result of a path to ground being supplied to one side of the relay coil.

So here is what you will need to figure out. When the car is at temp the relay should be closed . Question to answer, is there 12 volts at the relay?

You can manually force a relay to work or at least verify where to look for the problem ..

If you have a 3 wire relay pull one wire and see if you find 12 V repeat until you find voltage. If you see a wire and a jumper to another terminal on the relay that will be the 12v lead, see if you have voltage there. If you do good, none then there is the problem, trace back from there.

Now if the voltage is there then the question now becomes what is missing, one of the wires feeds the fans 12V after the relay is closed. The other is from the temp sensor and causes the coil to energize and that closes the relay contacts..

Have a meter, select ohms disconnect the fan plug at the fans , now just probe the fan plug and the relay to identify the wire that goes from the fan to the relay.. 0 ohms is the reading you want to see. Got it, now plug that wire back on the relay and reconnect the fans. We now know that the last wire not identified is the wire that is from the sensor . There are two ways to go from this point.

Here is what we have, we know that the voltage is at the relay, we know which wire is the wire that sends that voltage to the fan. We also know which wire is the signal or wire from the sensor.

You can, leave the wire from the sensor disconnected from the relay. Take another wire and just connect one end to a ground and touch the terminal that you removed the temp sensor wire from, if the relay is good it will turn on the fan, because you just completed the circuit to the relay coil and caused the contacts to close .

Another way would be to warm up the car and take a ohm reading from that sensor wire still disconnected from the relay to ground that would read 0 ohms only when the car is close or at temp, if it reads open after the car is warmed up the sensor is bad... This is all based on the fact that the harness is in good shape, no broken wires .
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