Our central air and heating system is not shutting off and it is blowing cool air. Does anyone know what causes this and how to stop it? Should we change the air filter? We have already changed the batteries in the thermostat.

Braeburn thermostate Non Programmable will not shut off A/C Blower in Attic

On most furnaces if one of the safety switch (i.e.inducer blower pressure switch, roll back switch, limit switch or even the circuit board fuse) is tripped (opens if its normally closed). The indoor fan will run continuously.
If you have good back ground in electricity or HVAC check all this switches for continuity since most of them are wired all together in series. DO NOT TRY TO JUMP this switches since they are there to protect your house from being burn down.

Man, somebody has some really slow internet service...

How do people even find these old threads? I rarely if ever get beyond the first page. I understand they are trying to help but maybe these folks should focus on the current threads and help those people.