{"product_id":"oem-lennox-limit-switch-20j99","title":"OEM Lennox Limit Switch — 20J99","description":"\u003cp\u003eThe genuine OEM Lennox \u003cstrong\u003e20J99\u003c\/strong\u003e limit switch is a critical safety control that monitors temperature inside your furnace heat exchanger and plenum. When temperatures climb beyond the safe operating threshold, this high-limit switch interrupts the burner circuit to prevent overheating, while also signaling the blower to run and clear excess heat. It is a frontline defense protecting both your Lennox furnace and your home.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCommon failure symptoms:\u003c\/strong\u003e A faulty \u003cstrong\u003e20J99\u003c\/strong\u003e can cause the furnace to short cycle — igniting and shutting off repeatedly — or fail to fire at all. You may also experience the blower running constantly, no heat on call, or a system that locks out on a limit fault. A switch that trips prematurely or sticks open leaves your furnace unable to complete a heating cycle.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhy OEM matters:\u003c\/strong\u003e Because this is a safety-rated component, the exact trip temperature and electrical rating must match your Lennox furnace design. The factory-original \u003cstrong\u003e20J99\u003c\/strong\u003e is calibrated to Lennox specifications, ensuring correct protection setpoints and reliable operation. Using a non-OEM substitute risks improper overheat protection and possible nuisance faults. Insist on genuine Lennox for safety and a precise fit.\u003c\/p\u003e","brand":"Lennox","offers":[{"title":"Default Title","offer_id":63081113125235,"sku":"LNX-20J99","price":19.95,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0984\/1190\/5395\/files\/nhvac-limit-switch-snap-disc-LNX-20J99.jpg?v=1783762479","url":"https:\/\/nationalhvacparts.com\/products\/oem-lennox-limit-switch-20j99","provider":"National HVAC Parts","version":"1.0","type":"link"}