On Wednesday I noticed my car's temp gauge reading at bottom while driving down the highway. The air conditioner was also non-functional. Each of these components were working fine the day before. The car continued operation, and I was able to drive it to a mechanic later that day.
My mechanic was unable to diagnose the problem, but also mentioned the thermostat couldn't close, causing too much coolant to flow and the engine to run much cooler than it should.
As I drove away from the mechanic the temp gauge showed the engine heating up short of where it normally is, and then malfunctioned during the drive. There was also a check engine light, but that went away on its own too.
So I guess... what could cause the temperature gauge, AC, and thermostat to fail almost at the same time?
Edit: Car is a 2006 Pontiac G6 GTP