{"product_id":"lennox-78h55-65209700-class-2-transformer-120v-to-24v-30va","title":"Lennox 78H55 65209700 Class 2 Transformer 120V to 24V 30VA","description":"\u003ch1\u003e\u003cstrong\u003eIntroduction: Lennox OEM Focus and System Function\u003c\/strong\u003e\u003c\/h1\u003e\n\u003cp\u003eThe Lennox 78H55 (Model 65209700) is the vital power-conversion \"brain\" for your furnace's control circuitry. As a genuine Class 2 transformer, its primary role is to step down 120VAC line voltage to a safe 24VAC output required for the thermostat, control board, and gas valve. It is a critical component for the Lennox Elite and Merit furnace series, ensuring that the low-voltage safety loop remains energized and stable. By using this specific OEM replacement, you guarantee the electrical isolation necessary to protect sensitive microprocessor-based control boards from high-voltage surges.\u003c\/p\u003e\n\u003ch2\u003e\u003cstrong\u003eKey Features:\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eGenuine OEM Fit (78H55):\u003c\/strong\u003e Engineered by Lennox for an exact bolt-on replacement, eliminating the need for custom mounting brackets or wire splicing in the blower compartment.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFixes \"Dead System\" Issues:\u003c\/strong\u003e Specifically designed to resolve no-power symptoms where the thermostat is blank and the furnace control board shows no LED diagnostic lights.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eClass 2 Safety Rated:\u003c\/strong\u003e Includes internal thermal overload protection to prevent the transformer from overheating or causing a fire if a low-voltage short occurs.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePrecision Voltage Regulation:\u003c\/strong\u003e Provides a stable 24V secondary output, which is essential for preventing relay \"chatter\" and noise in 24-volt contactors and solenoids.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOEM Reliability:\u003c\/strong\u003e Built with high-grade copper windings and a heavy-duty laminated core to ensure long-term durability in high-heat furnace environments.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003e\u003cstrong\u003eProduct Details:\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eBrand:\u003c\/strong\u003e Lennox\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eManufacturer:\u003c\/strong\u003e Genuine OEM\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePart Number:\u003c\/strong\u003e 65209700 (Cat # 78H55)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWeight:\u003c\/strong\u003e 1.5 lbs\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePrimary Voltage:\u003c\/strong\u003e 120 VAC \/ 60 Hz\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSecondary Voltage:\u003c\/strong\u003e 24 VAC\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePower Rating:\u003c\/strong\u003e 30 VA\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePhase\/Hertz:\u003c\/strong\u003e Single-Phase (1PH) \/ 60 Hz\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eClass:\u003c\/strong\u003e Class 2 Not Wet \/ Class 3 Wet\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003e\u003cstrong\u003e🛠️ HVAC Depot Pro Tip: The \"Short Circuit\" Check\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cp\u003eBefore installing the new 78H55 transformer, \u003cstrong\u003etake a picture of the primary (black\/white) and secondary (yellow\/blue) wiring.\u003c\/strong\u003e If your previous transformer \"burned out,\" there is likely a short in your thermostat wire or a bad contactor coil. Use a multimeter to check for 0 ohms between the 24V wires and ground. If you find a short, fix it before powering up the new transformer, or you will blow the new unit instantly.\u003c\/p\u003e\n\u003ch2\u003e\u003cstrong\u003eCross-Reference:\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eSuperseded Numbers:\u003c\/strong\u003e 100057-01, 89K59, 100057-02\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eLegacy Numbers:\u003c\/strong\u003e 652097, 68H5501\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDrawing Number:\u003c\/strong\u003e LB-53531A\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWhite-Rodgers\/Emerson Equivalents:\u003c\/strong\u003e 90-T40F3, 90-290Q\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003e\u003cstrong\u003eModel Compatibility:\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eG24\u003c\/strong\u003e (Suffixes: -045, -060, -075, -100, -120)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eG40\u003c\/strong\u003e (Suffixes: -045, -070, -090, -110)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eG50\u003c\/strong\u003e (Suffixes: -045, -070, -090, -110)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eG60\u003c\/strong\u003e (Suffixes: -070, -090, -110)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eG43\u003c\/strong\u003e (Suffixes: -045, -070, -090, -110)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eML180\u003c\/strong\u003e (Suffixes: E, XE, UH)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eML193\u003c\/strong\u003e (Suffixes: UH)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eEL180\u003c\/strong\u003e (Suffixes: NE, XE)\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"Lennox","offers":[{"title":"Default Title","offer_id":52451507732843,"sku":"66255112286","price":91.65,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0922\/9683\/9531\/files\/65209700-1.jpg?v=1773418599","url":"https:\/\/tophvacparts.com\/products\/lennox-78h55-65209700-class-2-transformer-120v-to-24v-30va","provider":"HVAC Parts and Equipment Depot","version":"1.0","type":"link"}