I have a Goodman furnace. Model # is GMP075-3. It was manufactured in 1993. Problem started with when the thermostat temp was reached... the flame would go out and the furnace would continue to blow cool air and not shut off. The only way to get it to shut off was to manually turn it off with the switch on the furnace. Now the same problem is happening but also it will not heat at all. It has tried to fire up and then quits rights away... then it just continues to blow cool air and won't turn off. Today it won't even try to fire up. Just blows cool air constantly. Themostat is set to heat... fan is on auto... temp set to 71. It is 60 in my house right now. The soonest I can get a repairman here is tomorrow afternoon. Hoping maybe someone has a simpler and less costly solution. The repairman suggested turning off the circuit breaker for 60 secs to reset the system. This worked once to get heat to blow... but then heat shut off and fan continued to blow cool air again. Since then I have tried resetting the circuit breaker and I can only get cool air... no heat. Ughhhhh...