Originally Posted by SilverTank
It's mounted after the radiator, so I'd say it qualifies as a puller. Don't really know what differentiates the two types, as it pulls from one side and blows on the other. It's not like an turbine which has a definate suck or blow action.
The PCM controls it, so it's tough to tell what the activation cycle is. It always seems to turn on with the A/C, so that indicates a duty cycle tied with that system. Not sure if it also activates under high heat without A/C. Mine has never activated in a "key off" situation; even in the Florida heat. This tends to indicate that it works only with the key in.
I'm still investigating the reason behind this fan, and what causes it to turn on. I've read lots of theories, but no official answer yet.
The PCM controls a relay that controls the fan. Failure mode is low speed fan. It's very rare that the PCM controls any high current devices. Things such as fuel pumps and ignition systems have their own power source, though there are exceptions. There is no duty cycle for the fan, it is either off or on, which I guess you could call a 100% duty cycle.
I should add that the fan is commanded on when the CHT or ECT gets to a certain point. If you disconnect CHT or ECT, which depends on the vehicle, the PCM will default to low speed fan just in case. It is possible to have a second circuit that would turn on the fan with the key off based on another temp sender. I don't know if any applications use that though.