Hi I have a Ducane CMPEV075U3 and my blower only runs for a few minutes then quits. I have a code that flashes in the diagnostics " pressure switch closed with inducer off" . When I jump the red and green from the thermostat it continues to work. Im not sure how the blower is affected by the pressure switch? Any ideas what my problem may be?

It sounds like a combustion air fan problem. It runs when you jump it out because you are pulling in the fan relay which is used in cooling mode and running fan on high instead of low or medium. See if the combustion air fan is seized up. I bet that's the problem. They don't last long due to the heat and combustion products like acids. You will most likely have to replace the combustion air fan and motor, and it's probably rusted badly, as usual.

It sounds like a combustion air fan problem. It runs when you jump it out because you are pulling in the fan relay which is used in cooling mode and running fan on high instead of low or medium. See if the combustion air fan is seized up. I bet that's the problem. They don't last long due to the heat and combustion products like acids. You will most likely have to replace the combustion air fan and motor, and it's probably rusted badly, as usual.

But it doesn't work in all modes, it is on ac all summer so the combustion fan wouldn't have even been running

Then you need to see what safety is in the fan relay circuit that shuts it off. Then you will need to go through it and see what is wrong by checking the motor and capacitor with a meter. There has to be some kind of safety turning it off. If it was my furnace I would rewire it if the control board was bad and put in an analog system because it's more reliable and simple, plus it's safe. The important thing is to find out which safety is turning it off because it doesn't make sense that any safety is tripping when it's in cooling mode unless something is wired wrong or the circuit board is bad. The safeties in the furnace are for the heating system because the only two electrical components working in cooling mode are the fan relay and the fan, nothing else controls the fan except sometimes a time delay is installed to keep the fan on a little while longer after the compressor turns off.

I leave my fan run 24/7/365, it's a vairable speed DC motor so replacing the control board isn't something I want to do. It has been trouble free for 5 years so if the fix isn't to costly I'm happy with the system. I also dsicovered it has a trouble code " pressure switch open with inducer off". I haven't tried the furnace as its still warm out but Im also wondering if it could be my programmable thermostat control as that is the connection I jump to get it to run. I will check to make sure that once it turns the fan on that it isn't turning it off as well.

If you jump it from "R" to "G" and it runs fine then the problem is in the thermostat. Sometimes they will act up when the backup batteries die. I have seen thermostats do all sorts of weird things when the batteries go dead. Try replacing them and see if that fixes it.