Fan question.

[Birdman330]

So I've noticed with this intense heatwave we're having that only one of the two radiator fans seems to run at idle with the A/C on. I decided to fiddle with the relay under the hood and then got the fan working, well it seemed it was working but now its back to the only one fan running and that is the left side fan. Is that normal or should both radiator fans be running? Because if so then I have to take a trip to the dealership and find out whats going on.

[TomPierce]

From the interwebz:

The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series parallel (S/P) configuration that allows the engine control module (ECM) to operate both fans together at low or high speeds, depending on cooling requirements. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block. The ground path is provided at G104.

During low speed operation, the ECM supplies the ground path for the low speed fan 1 relay through the fan 1 relay or low speed control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the FAN 1 fuse through the cooling fan motor supply voltage circuit to the right cooling fan. The ground path for the right cooling fan is through the cooling fan 2 relay and the left cooling fan. The result is a series circuit with both fans running at low speed.

During high speed operation the ECM supplies the ground path for the fan 1 relay through the fan 1 relay low speed control circuit. The ECM supplies a ground path for the high speed fan 3 relay and the fan 2 relay through the fan 2 relay or high speed control circuit. This energizes the fan 2 relay coil, closes the relay contacts, and provides a ground path for the right cooling fan. At the same time, the fan 3 relay coil is energized closing the relay contacts, and provides battery positive voltage from the FAN 2 fuse on the cooling fan motor supply voltage circuit, to the left cooling fan. During high speed fan operation, both engine cooling fans have their own ground path. The result is a parallel circuit with both fans running at high speed.

[Birdman330]

Basically the left side fan cools for the A/C if the engine gets too hot then the second fan will kick in.

[TomPierce]

Basically the left side fan cools for the A/C if the engine gets too hot then the second fan will kick in.

What you are saying reflects how you would expect a multi-fan system to operate. But I was curious that I never heard a second fan kick on, so I researched it with ALLDATA and found what I posted above.

Instead of a primary and secondary fan, the G8 runs both fans at a primary (low) or secondary (high) speed.

[laserred]

Not sure if this happened to you, but on my 2000 Grand Cherokee, when the car was turned on cold, the fan would run. As the fan motor got hot, the resistance increased to the point that the fan quit spinning. Was quite maddening troubleshooting it, but eventually found a way for the dealer to warranty it even though it was at about 85k miles. If you start the car with the AC on and both fans work, and then as the car gets hot the second fan quits, this is what I would think is happening. HTH.

[wreckwriter]

Basically the left side fan cools for the A/C if the engine gets too hot then the second fan will kick in.

Yup.

[Birdman330]

I have never come across this I'm used to both fans operating with the A/C on. Though from what others have been telling me this is normal operation for GM cars. That the left side is the main fan which is used during A/C operation which operates at high speed. Then what the tech at the Dealership told me is that if engine temperature exceeds 230 degrees then the second fan will kick on to assist in cooling down the engine back to normal operation temperatures then shut down. I'm not a huge fan of this type of set up I usually prefer an engine to run as cool as possible and with outside temperatures exceeding triple digits in both standard with heat index it makes the car work very hard and the engine to get hot real fast. But if that's the set up GM has it I won't change it. I'll put my trust in the set up, I think next year I'll throw in a high output Alternator and Deep Cycle Battery to assist with the A/C and fan. I have noticed with the A/C running the idle gets rough.