My Mother-in-law has a luxaire furnace. The flashing LED indicates
that the pressure switch is stuck open (2 flashes) - this is probably
because the fan with the pressure tube does not start. If I bypass the
control and run the motor straight from power, the switch now reports
stuck closed (which makes sense). If i pull the tube off and put it on
quickly the furnace will start no problem.

When I first looked at it, the switch wouldn't switch at all - I had
to clear out the tube going into the fan housing. Logic is telling me
that the issue is the control unit which isn't starting the fan, which
makes the sensor report stuck open - correct?

PS I did take the pressure switch off and test it - it works fine.
Before I go out and but the control unit I was just looking for a
second opinion.

Thanks!