I started a a/c install 3 days ago furnace is a nordyne kg7tc 2-stage that was installed 3 years ago with no issues.While do the low voltage wiring with new stat i deside to start furnace and check operation.status light is telling me pressure switch error so i take the tube off of inducer and work pressure manually through the tube and it closes i put tube on inducer furnace fires i cycle it again and it fires,today i go back to finish a/c install and i have the same issue.the furace will fire only after i blow in and out of the air tube connected to the inducer and its not the condensate switches either so what could cause this other than a replacement switch.