Make: York
Model or Series: TG9S
Type: 90% Furnace, Horizontal
Problem Description: Code 3 Pressure Switch Lockouts
Observed Symptoms: Furnace runs for a while then locks out.
Solution: Installed tee and air vent in rubber drain hose inside the furnace cabinet.
Additional Information: Furnace drain had a trap in the 3/4" pvc immediately after leaving the furnace cabinet.