2017 Cadillac XT5 - Cooling and AC issue

The Power Steering Assist warning, the engine Temp gauge buries itself to the lowest possible spot, the a/c stops working completely. A month earlier they “solved” this problem by replacing the thermostat as in addition to the above symptoms the temp guage would alternate between now working and maxing out as if the car was overheating. BOTH of these symptoms triggers the fan to come on … and it runs non stop but turns off promptly when you turn the car off.

You might want to have your mechanic check the alternator’s output. A failing alternator can result in all sorts of strange–and transitory–electronic malfunctions as the voltage varies.