The low fan is ac system activated , so don't look for a low fan with a bad ac system
The high fan is coolant temp activated at 105C , so you have high fan, but it seems to be cutting in a little late .. that is the blue 2 wire sensor on the thermo housing area.
The realys are behind the fuse box, under a lid that has to be unscrewed .. but you know fan works , so it is not a fuse problem.
I suspect sensor is a little out of spec.

If you a/c system is kaput and you have a lot of heat related driving to do, you can put a simple switch in the cabin that jumpers the high pressure sw at the reciever/drier and that will allow you to control the low fan circuit manually when you need them to get out of a jam. seeing the ac is not using them ,you might as well get something out of them , even if just for emergency back-up.