I have a payne furnace which is not woking,the code flashes 24,and it says something about a 24 vac line open,how do I repair this

Sounds like a pressure switch problem. Take the top door off the furnace. Look for the vent motor. There will be a small rubber tub coming off going to a round switch. Take that tube off and gently blow and suck into it. This should free the switch. Also chck to make sure the vent motor is spinning and not making a loud noise