AC Always runs!

Help! 2015 Fitz Coronado 12.7 series 60. 1.These came with a coolant shut off valve to the heater core. That is off. Seems I have no control of AC. It’s either always on or I gotta press the AC button to shut it off.
2. Random throughout the day, or not at all, suddenly the engine temp gauge will swing wildly from very low up to 200+. High Coolant temp message appears, check engine and engine shut down come on for a few seconds, engine fan comes on and runs for 30 seconds or so. Then all goes back to normal.... WTH! . This may happen 20 times per day or not at all. Parked or running down the road.

 

No, no defrost on.
I know these may or may not seem like two separate issues and maybe they are.

 

AC relay? I’ve not heard of this device. What is it and where is it located?

 

Thanks 423! So would this relay also control the in cabin temperature? Right now I have the temperature control all the way over to the hot side But if I push the AC button the AC will work continually until I turned it off. It does not cycle to control the temperature and the only way I can do that is to manually Push the AC button off and on.