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Fan on Fan off

AZbowhunter's Avatar

Join Date: Aug 2002
Posts: 148

04-24-05, 03:26 AM   #1  
Fan on Fan off

1988 Nisson Max. 6cyl.
This car has two cooling fans and two temp. sencor Sw.
The prob. is that it is over heating.
One of the fans was on but the other one was not (I think that the second one should come on when the temp. exceeds ?).
I ck. the book and it said to ck. fan motor. I disconnected the wire plug and jumped the the fan with the battery. Fan worked fine. Next it said to ck. the sencor. I removed it and put it in boiling water checking the wires with Ohm. meter for resistence. Nothing happened. Put it back in and jumpered the conn. that has the power to the the sw.
Started the car to try and get it to heat up so the fans would come on. Car heated up to norm., but fans did not come on. Keep car running to try and heat it up more; did not heat up more.
Turned on the air cond. and both fans came on (one fan still jumpered). Shut off car and reconn. the sencor sw.; then started car turned on air cond. and both fans came on.


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chevydrivin's Avatar

Join Date: Apr 2005
Posts: 242

04-24-05, 04:26 AM   #2  
I would get a jumper wire from battery straight to fan and see if it works. If it does not then its the motor. If t does then you have to troubleshoot from there. If motor runs when jumped and you can't find why it won't run just jump the good fan hot wire over and let both run on the same wire.

jeff67's Avatar

Join Date: Dec 2001
Posts: 616

04-24-05, 04:29 AM   #3  
Posted By: AZbowhunter Next it said to ck. the sencor. I removed it and put it in boiling water checking the wires with Ohm. meter for resistence. Nothing happened.
Does this mean the sensor is good? If so, you may have a bad relay or switch, the one you were jumpering.

ASEPartsman's Avatar
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04-24-05, 04:36 PM   #4  
One of the fans is supposed to come on only when the air conditioner is in use to help supply additional air the the condenser.

carguyinva's Avatar

Join Date: Nov 2003
Posts: 1,147

04-25-05, 12:39 AM   #5  
for the record...

...you can't get a coolant fan switch hot enough in boiling water. since water boils at 212 and cooling systems run typically at 225 or hotter before fans will come on, you can't get them hot enough on the stove. as a rule, 1 fan is sufficient to keep the engine from over heating except in the hottest of conditions. the second fan may be a condenser only fan...depends on the manufacturer's desire. a wiring diagram will prove the fan control strategy for sure...there are many control strategies and without consulting some information, just assuming both fans should run may lead you down the wrong path.

let's back up...how do you know it's overheating? does it actually boil over or is it just the guage indicating?? perhaps just the guage sending unit is in question. does it have the original radiator in it? if so, it's out lived it's average life span...checking the temp in different areas of the rad with a temp gun helps to decide...

there are many questions to ask and answer about over heating...

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