[QUOTE=murphysf;1500563]Hello

I am trying to understand the operation of the AUX fan that is mounted on the front of the radiator. I have searched previous posts and also on google, lots of information but some details are still missing.

To make things simple, let me ask two questions:

If the AC is off what conditions need to happen for the AUX fan to come on?

The coolant temp has to reach 105C..this is fan high speed.

If AC is on what conditions need to happen for the AUX fan to come on?

The a/c high side pressure switch detects a high thermal load and triggers the fan relay. This is low fan..