Arrived at location on 6/23/22 - found unit displays SFT WHEN THE TEMPERATURE WOULD GET NEAR SET POINT. FOUND THE AIR SWITCH IS OPENING. FOUND AIR SWITCH IS BAD ,CHECKED FILTER APEARS TO BE OK. ID REPLACE A MISSING SCREW ON THE DOOR CATCH AND TIGHTENED THE DOOR HINGES. I WILL OBTAIN PARTS AND RETURN. Returned to location on 7/12/22 - Replaced the air switch and tube I checked operation .ok ready to use.