Ok so I havent gotten to pulling out the tstat yet (my stressed brain was thinking you meant something inside the furnace (hence the car tstat reference), boy did I feel like an idiot this morning when it finally hit me lol) but I did get everything quiet in the house and found that the A/C does...
The system was put in just 4 years ago with an energy assistance package from our electric company and it was new when they installed it. It's a Payne (love the irony), model number pg9mab036080acsa
I have to manually flip the switch on the furnace that turns it on/off otherwise it will just run forever which is a PITA to run up and down the stairs 4-7 times a day. I have never chatted about this stuff before so I have no idea at all what information you need so you're going to have to ask...