{"product_id":"tempstar-40va-transformer-for-t9mvx100l20a1-115v-to-24v-ships-today","title":"Tempstar 40VA Transformer for T9MVX100L20A1 — 115V to 24V | Ships Today","description":"\u003ch3\u003eOverview\u003c\/h3\u003e\n\u003cp\u003eThis is the OEM control transformer, part number 1172810, for the Tempstar T9MVX100L20A1 two-stage variable-speed gas furnace. It steps 115V line voltage down to the 24V used by the furnace control board, thermostat, gas valve, and safety circuits, and is rated at 40VA. When a control transformer fails, the entire low-voltage side of the system goes dead: no thermostat display, no call for heat or cooling, and no 24V at the board. Transformers commonly fail from a shorted thermostat wire, a seized blower or contactor drawing excess current, or simple age. Replacing it with the correct 40VA OEM unit restores full control power.\u003c\/p\u003e\n\n\u003ch3\u003eSpecifications\u003c\/h3\u003e\n\u003ctable\u003e\n\u003cthead\u003e\u003ctr\u003e\n\u003cth\u003eSpec\u003c\/th\u003e\n\u003cth\u003eValue\u003c\/th\u003e\n\u003c\/tr\u003e\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eOEM Part Number\u003c\/td\u003e\n\u003ctd\u003e1172810\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eType\u003c\/td\u003e\n\u003ctd\u003eControl Transformer\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBrand\u003c\/td\u003e\n\u003ctd\u003eTempstar (ICP \/ Heil)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003ePrimary Voltage\u003c\/td\u003e\n\u003ctd\u003e115V\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSecondary Voltage\u003c\/td\u003e\n\u003ctd\u003e24V\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eRating\u003c\/td\u003e\n\u003ctd\u003e40VA\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eFits Model\u003c\/td\u003e\n\u003ctd\u003eT9MVX100L20A1\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003ch3\u003eCompatibility\u003c\/h3\u003e\n\u003cp\u003eDirect-fit replacement for the Tempstar T9MVX100L20A1 100,000 BTU two-stage variable-speed furnace. This 40VA 115V-to-24V transformer is used across the ICP\/Tempstar\/Heil\/Comfortmaker furnace family. Confirm primary\/secondary voltage and VA rating against your existing transformer before installing.\u003c\/p\u003e\n\n\u003ch3\u003eInstallation Guide\u003c\/h3\u003e\n\u003col\u003e\n\u003cli\u003e\n\u003cstrong\u003eSafety First\u003c\/strong\u003e — Disconnect electrical power at the furnace switch or breaker. Verify zero voltage with a multimeter.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAccess\u003c\/strong\u003e — Remove the furnace control\/blower door to reach the transformer and control board.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDocument\u003c\/strong\u003e — Photograph the primary (line) and secondary (24V) wiring before disconnecting anything.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eRemove\u003c\/strong\u003e — Disconnect the primary and secondary leads, remove the mounting screws, and take out the old transformer.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eInstall\u003c\/strong\u003e — Mount the new transformer, reconnect primary to line and secondary to the 24V circuit per your photo.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTest\u003c\/strong\u003e — Restore power, confirm 24V at the secondary terminals, and verify the thermostat and furnace respond.\u003c\/li\u003e\n\u003c\/ol\u003e\n\n\u003ch3\u003eSigns You Need a Replacement\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eBlank thermostat and no response from the furnace.\u003c\/li\u003e\n\u003cli\u003eNo 24V output measured at the secondary terminals.\u003c\/li\u003e\n\u003cli\u003eBlown low-voltage fuse that fails again immediately.\u003c\/li\u003e\n\u003cli\u003eBurnt smell or visibly scorched transformer housing.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eShipping \u0026amp; Returns\u003c\/h3\u003e\n\u003cp\u003eShips same day on orders placed before 3 PM CST. 30-day returns. Backed by the National HVAC Parts fitment guarantee.\u003c\/p\u003e","brand":"Tempstar","offers":[{"title":"Direct Replacement","offer_id":63021677314419,"sku":"1172810-GEN","price":29.0,"currency_code":"USD","in_stock":true},{"title":"OEM","offer_id":63048408531315,"sku":"1172810","price":37.7,"currency_code":"USD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0984\/1190\/5395\/files\/nhvac-transformer-control-1172810_42e7fd84-9f7e-4a93-a029-401200d0490f.jpg?v=1782958453","url":"https:\/\/nationalhvacparts.com\/products\/tempstar-40va-transformer-for-t9mvx100l20a1-115v-to-24v-ships-today","provider":"National HVAC Parts","version":"1.0","type":"link"}