Heil Furnace - exhaust fan comes on but the ignitor does not lite. It is because the pressure switch is not to pressure. I remove the vacuum line to the burner chamber and then the igintor comes on. If I place the vacuum line back on the burner chamber the ignitor goes out and the furnace does not lite. If I leave the vacuum line off the furnace works fine. I have checked all the vacuum lines and they are clear. What could be the problem?

The air flow switch could be the issue.

Is the air flow switch the pressure switch? I forgot to mention that I bought a new pressure switch and installed it and it did not fix the problem. About an hour ago I pulled the vacuum hose off the combustion fan and sucked on the hose and the pressure switch pulled in and the ignitor energized. But once I hooked it all back up I still have the same problem.