{"product_id":"oem-lennox-pressure-switch-57m66","title":"OEM Lennox Pressure Switch — 57M66","description":"\u003cp\u003eThe genuine OEM Lennox \u003cstrong\u003e57M66\u003c\/strong\u003e pressure switch is a furnace safety device that verifies proper combustion venting before ignition. Wired to your furnace control board, it senses the negative pressure created by the draft inducer motor and closes its contacts to prove that flue gases are being drawn out of the heat exchanger. Only then will the sequence advance to open the gas valve and light the burners.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCommon failure symptoms\u003c\/strong\u003e include the furnace failing to ignite, cycling on and off without producing heat, or a diagnostic code indicating an open pressure switch. A worn diaphragm, a cracked or clogged sensing hose, condensate blockage, or a restricted vent can all keep the \u003cstrong\u003e57M66\u003c\/strong\u003e from closing, causing the furnace to lock out as a protective measure.\u003c\/p\u003e\u003cp\u003eOEM matters here because pressure switches are calibrated to a precise trip point in inches of water column that is specific to each Lennox furnace model. Installing a mismatched aftermarket switch can lead to unsafe firing or persistent nuisance faults. The \u003cstrong\u003e57M66\u003c\/strong\u003e is built to exact Lennox factory specifications for correct calibration, a proper physical fit, and dependable long-term safety.\u003c\/p\u003e","brand":"Lennox","offers":[{"title":"Default Title","offer_id":63081102082419,"sku":"LNX-57M66","price":24.95,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0984\/1190\/5395\/files\/nhvac-pressure-switch-single-LNX-57M66.jpg?v=1783763056","url":"https:\/\/nationalhvacparts.com\/products\/oem-lennox-pressure-switch-57m66","provider":"National HVAC Parts","version":"1.0","type":"link"}