1999 cooling fan will not operate

[brcidd]

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?

[djjm3]

Originally Posted by brcidd

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....

[djjm3]

Originally Posted by maxwedge

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....

[djjm3]

Originally Posted by j cAT

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??

[maxwedge]

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.

[djjm3]

Originally Posted by maxwedge

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......