Usually a vaccum line falls under the hood, look for a line that's not connected, and reconnect. Usually these lines go through the firewall so that would be the place to look
FUSE!
check crank sensor
Where the air blows out control are vacuum operated.A more common problem is when the air is stuck on defrost only.The cause is essentially the same, so check out the "Related Question" below for where to go next
After repairing the cause of the code, you can clear it with a scan tool.
Faulty plug wires or bad coil or coil wire.
most likely your heater controls run via vacuum lines. cracked or broken lines could cause this.
It could be the spark plug wires that's what was wrong with mine.
One blown bulb or fuse could cause this problem.
Something can be taxing the work of the alternator, or the alternator can be weak and needs replaced.
Starter dragging? Bad starter Fuel injectors leaking causing a flooding situation?
The most common cause would be low refrigerant.
Check bulbs Check fuse for parking/tailights Could be a bad switch