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Old 11-21-2012, 06:21 PM   #16
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Re: 1999 cooling fan will not operate

Coolant fans won't come on with a/c UNLESS there is 175 psi a/c pressure generated (On GM W-cars as is yours) So does your a/c work? Is It capable of 175 psi head oressure?
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Old 11-21-2012, 08:55 PM   #17
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Re: 1999 cooling fan will not operate

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Originally Posted by brcidd View Post
Coolant fans won't come on with a/c UNLESS there is 175 psi a/c pressure generated (On GM W-cars as is yours) So does your a/c work? Is It capable of 175 psi head oressure?



compressor dosent engage....
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Old 11-21-2012, 08:57 PM   #18
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Re: 1999 cooling fan will not operate

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You can command the fans on with a pro scanner to see if the pcm can operate them, also if you unplug the coolant temp sensor they should come on.
When I pull the sensor connector both fans WORK....when i reconnect, they stop....
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Old 11-21-2012, 09:15 PM   #19
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Re: 1999 cooling fan will not operate

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Originally Posted by j cAT View Post
85-86 is the coil control. 86 is the ground.

87 should go to the fan , 30 is the 12 volt feed. short out 87 to 30 does fan work ? is there 12 volts across the fan power input. do not use body ground use the return wires/ground wire.

the fat wires go to the fan motor , the small wires are the contol coil relay wires.

your finds appear wrong .

If you are facing the fuse block.
The fat green wire is left front. the thin dark green one is to the right front

do you have a diagram??
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Old 11-22-2012, 09:17 AM   #20
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Re: 1999 cooling fan will not operate

If the fans work sensor disconnected the circuits are all good, the pcm does this as a default to prevent overheating when it cannot read engine temp. So now get a scanner on it and watch the temps, as they approach 222, the fans should come on, reconnect sensor of course.
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Old 11-23-2012, 01:34 AM   #21
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Re: 1999 cooling fan will not operate

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Originally Posted by maxwedge View Post
If the fans work sensor disconnected the circuits are all good, the pcm does this as a default to prevent overheating when it cannot read engine temp. So now get a scanner on it and watch the temps, as they approach 222, the fans should come on, reconnect sensor of course.
Will try that next......
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