I have a carrier 1994 gas furnace. When I turn furnace on the blower starts running for 90 seconds throws code 12 then when inducer motor starts it throws code 31. Inducer motor will shut back down. What could be the problem?

You have a problem with the switch that proves the combustion air blower. It could be the switch or the hose. You will need to test it with a meter to find out which it is. Here is a manual on using a meter: https://dl.dropbox.com/u/8010163/How%20to%20use%20Test%20Equipment%20Service%20Manu al.pdf