Odd problem with a/c thermostat

Thanks folks. I've learn a lot. I'm replacing the sensor. BTW, the sensor is mounted just adjacent to an ac return register. When I remove that register I can access the wiring fortunately so it won't be difficult to switch out. I noticed however that with the AC running there is a lot of cool air blowing on my hand as if there is a hole in the duct work. This doesn't occur in any of the other intake ports. This one however is the closest one to the ac unit. Curious.