MY COOLING FAN ONLY RUNS WITH THE A/C ON

  • Tiny
  • Csm1992
  • 1987 BUICK CENTURY
  • 83,000 MILES

I recently acquired a 1987 Century with the 2.5L engine. The car runs great however the cooling fan only runs with the A/C on. I checked a basic wiring diagram and find that the wire from the ECM to the fan is grn/yellow. There is a plug near the fan hanging in space that has two wires: grn and grn/yellow. The problem is I can't find a home for it. The plug that goes on the fan has a blk and blk/red wire and there are no other plugs. I even checked at the parts store to see if it had the wrong fan and no it apparently has the correct fan. Traced the black and red wire up the harness a bit looking for another plug but no luck. Any suggestions?

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Tuesday, September 25th, 2012 AT 9:12 PM

14 Replies

  • Tiny
  • Saturntech9
  • EXPERT
  • 30,228 POSTS

Does your temp gauge work?Also do you have a multimeter to do some testing?

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Tuesday, September 25th, 2012 AT 9:18 PM
  • Tiny
  • KHLow2008
  • EXPERT
  • 41,984 POSTS

Check the coolant fan switch located on upper left side of engine, at end of exhaust manifold. It has a Dark Green/White wire.

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Tuesday, September 25th, 2012 AT 9:24 PM
  • Tiny
  • Csm1992
  • MEMBER

I am an above average shadetree mechanic and have tools etc. The plug in question has grn and grn/yellow wires. The coolant temp sensor has one wire attached.

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Tuesday, September 25th, 2012 AT 9:33 PM
  • Tiny
  • Saturntech9
  • EXPERT
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Post a pic of the connector showing it and where its located. The single wire is the gauge the two wires is the coolant temp sensor connector

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Tuesday, September 25th, 2012 AT 9:44 PM
  • Tiny
  • Saturntech9
  • EXPERT
  • 30,228 POSTS

It says the temp sensor is on left side of engine bellow coolant outlet.

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Tuesday, September 25th, 2012 AT 9:47 PM
  • Tiny
  • Cadieman
  • MEMBER

Find the fan relay try swapping the relay with another 1.I would replace the coolant sensor that is what controls the fan oper. It grounds the fan relay to turn the fans on when the a/c is off.

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Tuesday, September 25th, 2012 AT 11:24 PM
  • Tiny
  • Saturntech9
  • EXPERT
  • 30,228 POSTS

If the fan comes on with the ac I would say the fan relay is working wouldn't you cadieman?

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Tuesday, September 25th, 2012 AT 11:49 PM
  • Tiny
  • Cadieman
  • MEMBER

Yes but the coolant temp. Sensor tells the cpu when to turn the fans on when the temp. Is to high. The fans are turned on auto. As soon as u turn the a/c on.

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Wednesday, September 26th, 2012 AT 1:37 AM
  • Tiny
  • Saturntech9
  • EXPERT
  • 30,228 POSTS

Correct but the same relay is used to turn the fan on at the correct temp or when the ac is turned on. So when you said to check the relay that's why I said what I said.

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Wednesday, September 26th, 2012 AT 1:48 AM
  • Tiny
  • Cadieman
  • MEMBER

I was thinking the a/c grounds the relay directly from the a/c head when turned on. When u let the sensor ground the relay thats from the temp. Sensor. So u have 2 circuts controlling the fan funshion by grounding the relay.1 is the cts and the other is the a/c head. Seeya tomarrow im falling asleep. Ltr

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Wednesday, September 26th, 2012 AT 2:54 AM

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