I get a 3 minute beep code says the pressure switch is open and needs to be closed. Isn't it in the front where you put the cover back on? It is a Armstrong air ultra 80 V 45647-001. It comes on for a few seconds then goes back off. I took the
Cover off the other day to see how dirty it was and also to see if I could find the filter to replace it. New furnace to me so was trying to find filter spot. Now it won't come on. It is cold outside and going to get colder tonight. Would really like to fix it without landlord having to call a high priced repair man to fix the minor problem.