My cooling fan only runs with the A/C on

1987 BUICK CENTURY
83,000 MILES
Avatar
CSM1992
  • MEMBER
  • 6 POSTS
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?
Sep 25, 2012 at 9:12 PM
Advertisement
Avatar
SATURNTECH9
  • CERTIFIED EXPERT
  • 30,869 POSTS
Does your temp gauge work?also do you have a multimeter to do some testing?
Sep 25, 2012 at 9:18 PM
Avatar
KHLOW2008
  • CERTIFIED EXPERT
  • 41,814 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.
Sep 25, 2012 at 9:24 PM
Advertisement
Avatar
CSM1992
  • MEMBER
  • 6 POSTS
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.
Sep 25, 2012 at 9:33 PM
Avatar
SATURNTECH9
  • CERTIFIED EXPERT
  • 30,869 POSTS
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
Sep 25, 2012 at 9:44 PM
Avatar
SATURNTECH9
  • CERTIFIED EXPERT
  • 30,869 POSTS
It says the temp sensor is on left side of engine bellow coolant outlet.
Sep 25, 2012 at 9:47 PM
Avatar
CADIEMAN
  • CERTIFIED EXPERT
  • 3,544 POSTS
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.
Sep 25, 2012 at 11:24 PM
Avatar
SATURNTECH9
  • CERTIFIED EXPERT
  • 30,869 POSTS
If the fan comes on with the ac I would say the fan relay is working wouldn't you cadieman?
Sep 25, 2012 at 11:49 PM
Avatar
CADIEMAN
  • CERTIFIED EXPERT
  • 3,544 POSTS
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.
Sep 26, 2012 at 1:37 AM
Avatar
SATURNTECH9
  • CERTIFIED EXPERT
  • 30,869 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.
Sep 26, 2012 at 1:48 AM
Avatar
CADIEMAN
  • CERTIFIED EXPERT
  • 3,544 POSTS
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
Sep 26, 2012 at 2:54 AM
Avatar
SATURNTECH9
  • CERTIFIED EXPERT
  • 30,869 POSTS
The wire diagram shows one ac trigger and again it uses the same relay.
Sep 26, 2012 at 3:00 PM
Avatar
CADIEMAN
  • CERTIFIED EXPERT
  • 3,544 POSTS
1 relay controls both this is true saturntech9. only different is one comes directly from the a/c head directly to the relay.the other uses the cts to cycle the fans.hope this guy comes back.we need to know if it has a coolant temp.readout in the dash.for the price of cts just replace it.
Sep 26, 2012 at 9:35 PM
Avatar
SATURNTECH9
  • CERTIFIED EXPERT
  • 30,869 POSTS
Actual in the diagram it shows one trigger point for the fan relay when.i looked up the fan diagram looks like the trigger point comes from the computer if it turns on from ac being on or the computer turning it on from the coolant temp input.
Sep 26, 2012 at 10:02 PM
Avatar
CADIEMAN
  • CERTIFIED EXPERT
  • 3,544 POSTS
we you turn on the air it sends power to the ac clutch directly from the a/c head.the trigger is must be from the cts.buddy im done on this 1 and im going on to greener pastures.talk to u ltr.
Sep 27, 2012 at 3:16 AM