gas valve

Paul S_3

On a 90 plus furnace with a differential pressure switch, what is the purpose when the gas valve has a fitting hooked up to the positive side of the pressure switch teed in with the burner compartment?im working on a Bryant 90 plus mod# 398aav036080aaka ive found a bad gas valve and i was just wondering ...ive seen them on other types of equipment Thanks paul s

Steve Minnich

It's there to provide a reference of the slightly negative pressure in the burner box to keep the furnace firing rate correct.

Paul S_3

Thanks for reply but Why does it run with it off ? Thanks Paul s

Paul S_3

Gas valve

Steve Minnich

It will run without off. It just won't run at the firing rate it's designed to run at. I don't think the earliest of Plus 90's used that but I have a 398 manual right after they made the change.