If the fan comes on with the A/C, then high speed is working.
Here's a question that requires some assistance to answer: At what temp is "M" on the dial? It's not very accurately calibrated, plus I wouldn't trust it unless I had already replaced the sensor (Ford has had TSBs on both reading very low, and very high, due to bad crimps and assembly ... I would Just Replace It, the one for the gauge anyway.)
I would also stick a meter on the low speed side and see if the low speed is getting voltage. Then back track to the IRCM and see if IT is getting signal from the ECU to turn the low speed on.