Trane VAL3519 Gas Valve 321894 706 The bulb must be mounted The bulb must be mounted on a horizontal run of the suction line at the 10 o'clock or 2 o'clock position and must be fully wrapped in the supplied insulation to avoid influence from ambient air temperatures This adjustable limit switch is a direct fit solution for technicians servicing Trane air handlers and rooftop units this OEM component provides the specific flow characteristics required to meet factory specifications and maintain safe operating parameters for the heat exchanger effectively eliminating issues like delayed ignition or intermittent burner hangups