Sometimes when I idle, the A/C fails to run (you hear it click, there is an "air" sound from the dashboard, but it blows warm a for a few seconds and then the compressor gives up and shuts off.

I suspect it's the radiator fan as I was using the Versa to jumpstart my Saturn the other day and, even though idling for a long while, the radiator fan never clicked on and I could smell anti-freeze.

The fan does kick on-sometimes (I drove to work this morning and checked when I parked - it was running. But I don't think it was running all that fast.)

Are these fans variable speed?

If so, what determines when and at what speed they run?

Are they prone to failure (the fans, the relays, temp sensors, or the connectors, etc.)?

I tried unplugging the fan last night to run power from battery to test it, and couldn't get the plug out to save my life. Anyone have any experience with that?

Thanks!

The fans from what I know are not variable speed. They can; however, fail due to a faulty fan motor. It's mostly common between those made from 2012-2015 (N17 pre-facelifts). I had the pleasure of boiling my thermostat as a result of the fan motor's failure.