{"product_id":"factory-authorized-parts™-hh18ha502-furnace-high-limit-safety-switch-135-f-175-f-auto-reset","title":"Factory Authorized Parts™ HH18HA502 Furnace High Limit Safety Switch 135°F-175°F Auto Reset","description":"\u003ch1\u003eFactory Authorized Parts™ HH18HA502 Furnace High Limit Safety Switch 135°F-175°F Auto Reset\u003c\/h1\u003e\n\u003ch2\u003eThe Precision Thermal Monitor\u003c\/h2\u003e\n\u003cp\u003eThe \u003cstrong\u003eHH18HA502\u003c\/strong\u003e is a primary \"LS1\" limit switch engineered to serve as the critical safety \"brain\" for high-efficiency Carrier, Bryant, and Payne gas furnaces. This genuine Factory Authorized Part is responsible for monitoring the internal temperature of the heat exchanger assembly. By acting as a constant thermal gatekeeper, it prevents the furnace from reaching hazardous temperatures that could lead to equipment failure or fire. If airflow is restricted—causing a rapid rise in heat—this switch interrupts the control circuit to shut down the burners, only allowing operation to resume once temperatures have returned to safe, engineered levels.\u003c\/p\u003e\n\u003ch2\u003eKey Features\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eGenuine OEM Replacement:\u003c\/strong\u003e Specifically designed as part number \u003cstrong\u003eHH18HA502\u003c\/strong\u003e to maintain the original safety certifications and factory warranty of your HVAC system.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePrecision Temperature Calibration:\u003c\/strong\u003e Engineered to \"Open\" (Cut-out) at \u003cstrong\u003e175°F\u003c\/strong\u003e and \"Close\" (Cut-in) at \u003cstrong\u003e135°F\u003c\/strong\u003e, ensuring the furnace operates within a narrow, safe thermal window.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAutomatic Reset Technology:\u003c\/strong\u003e Features a bi-metal disc that automatically resets the heating cycle once the system cools, eliminating the need for manual intervention during temporary airflow fluctuations.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSystem Integrity Protection:\u003c\/strong\u003e Prevents premature cracking of the heat exchanger by ensuring the furnace never exceeds its maximum design temperature.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eVibration-Resistant Terminals:\u003c\/strong\u003e Equipped with heavy-duty spade connectors designed to withstand the constant vibrations of the blower motor and inducer assembly.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003eProduct Details\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eBrand:\u003c\/strong\u003e Factory Authorized Parts™ (Carrier\/Bryant\/Payne)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eManufacturer:\u003c\/strong\u003e United Technologies \/ Carrier Corp\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePart Number:\u003c\/strong\u003e HH18HA502\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWeight:\u003c\/strong\u003e 0.10 lbs\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eVoltage:\u003c\/strong\u003e 24V (Control Circuit)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAmps\/Watts:\u003c\/strong\u003e 0.5A @ 24VAC (Pilot Duty)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOpen Temperature:\u003c\/strong\u003e 175°F\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eClose Temperature:\u003c\/strong\u003e 135°F\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eReset Type:\u003c\/strong\u003e Automatic Reset\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003e🛠️ HVAC Depot Pro Tip\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003e\"Check the Coil!\"\u003c\/strong\u003e If you are replacing a tripped HH18HA502, don't stop at the air filter. A frequent cause for this switch opening at 175°F is a dirty \u003cstrong\u003eA-Coil (Evaporator Coil)\u003c\/strong\u003e located above the furnace. Even with a clean filter, a clogged coil blocks airflow and causes heat to back up into the heat exchanger. \u003cstrong\u003eTake a picture\u003c\/strong\u003e of the switch orientation before removal to ensure the sensing element is positioned exactly in the center of the airflow path for accurate monitoring.\u003c\/p\u003e\n\u003ch2\u003eCross-Reference\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eLegacy \/ Superseded Numbers:\u003c\/strong\u003e HH18HA451, HH18HA457\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDrawing Numbers:\u003c\/strong\u003e 313362-457, 1NT01L-4577\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eEquivalent Brands:\u003c\/strong\u003e ICP (Heil, Tempstar, Comfortmaker), White-Rodgers \/ Emerson\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003eModel Compatibility\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003e58STA\/STX Series\u003c\/strong\u003e (Suffixes: 045-12, 070-12, 090-14, 090-16, 110-20)\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e310A\/J Series\u003c\/strong\u003e (Suffixes: 024045, 036070, 048090, 060090, 066110)\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e912S\/915S Series\u003c\/strong\u003e (Suffixes: 30040S, 42060S, 48080S, 60100S)\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003ePG8M Series\u003c\/strong\u003e (Suffixes: 045045, 070070, 090090, 110110)\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e58SB\/SC Series\u003c\/strong\u003e (Suffixes: 040-12, 070-12, 090-16, 110-20)\u003c\/p\u003e","brand":"Carrier","offers":[{"title":"Default Title","offer_id":52451503145323,"sku":"662442554260","price":35.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0922\/9683\/9531\/files\/HH18HA490_9516d0cd-57ba-46c3-b30e-1d9ea6087f6b.jpg?v=1772041426","url":"https:\/\/tophvacparts.com\/products\/factory-authorized-parts%e2%84%a2-hh18ha502-furnace-high-limit-safety-switch-135-f-175-f-auto-reset","provider":"HVAC Parts and Equipment Depot Open To Homeowners and Contractors","version":"1.0","type":"link"}