Overheating: How do I check a radiator fan and sending unit?

I have a SN95 that is beginning to overheat. About 3 weeks ago, I converted to a 160 degree thermo when I had a custom chip installed. The car runs stronger and harder but just a couple of days ago, it erratically began to heat up.

It use to be on the 'N' and would rarely move. Now, after a driving an hour, it will go over to the 'A'. Today, when I was parking, I turned off the A/C, let it idle and the meter went over to the 'L'.

I got out to check on the fan while the car was still idling. The fan was off.

Should the fan have been on?

Oh yeah, I have a new radiator, radiator cap, water pump and frespkv

How do I check whether there is a problem with the fan or the sending unit?
Could it be something else?

Thanks for that info. I've had some recall work done (the hood and the parking brake, which got worse after they fixed it) but not the fan. I'll check on that.