My blower motor isn't shutting off after my heat shuts off, causing it to blow cold air into my house. I suspect that the fan limit switch is bad, but the furnace has at least four limit switches. Are these all tied to the blower motor? I'm not sure which ones I should check for the fan limit switch. I'm confident it isn't the thermostat as I swapped it out with another one and had the same issue. It continues to run even after I put the thermostat in the off position.
Your control board's likely shot
On a newer furnace like yours, the fan limit/thermostat function is performed by the control board and its onboard fan relay. This means that a continuously running blower is generally the fault of the fan relay getting welded shut, or occasionally something else failing inside the control board's logic. Either way, replacing the control board should cure the issue.