Tempstar 40VA Transformer for T9MPX100L20A2 — 115V to 24V Step-Down | Ships Today
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Overview
This OEM control transformer (part number 1172810) steps 115V line voltage down to the 24V low-voltage power your Tempstar T9MPX100L20A2 furnace needs to run its control board, thermostat circuit, gas valve, and ignition system. Rated at 40VA, it supplies steady, regulated low-voltage power to every 24V component in the furnace. When a transformer fails, the entire control circuit goes dead: the thermostat display blanks out, the furnace will not respond to a call for heat, and the control board shows no power. A buzzing transformer, a tripped internal fuse, or a burnt-smelling control compartment are all classic signs of a failed or overloaded transformer. Replacing it with a genuine OEM 40VA unit restores correct voltage and protects the rest of your control circuit.
Specifications
| Spec | Value |
|---|---|
| Part Number | 1172810 |
| Type | Step-Down Control Transformer |
| Brand | Tempstar (ICP / Heil) |
| Primary Voltage | 115V |
| Secondary Voltage | 24V |
| Rating | 40VA |
| Fit | OEM Direct Replacement |
Compatibility
Engineered as a direct OEM fit for the Tempstar T9MPX100L20A2 gas furnace. The same 1172810 transformer is shared across many ICP-family furnaces sold under the Tempstar, Heil, Comfortmaker, and Carrier/Bryant-built ICP lines. Always confirm your existing transformer is a 115V-to-24V 40VA unit before installing.
Installation Guide
- Safety First — Disconnect power at the furnace switch and breaker, then verify zero voltage with a multimeter.
- Access — Remove the furnace control/blower service panel.
- Document — Photograph all primary and secondary wire connections before disconnecting.
- Remove — Disconnect the 115V primary and 24V secondary leads, then unbolt the failed transformer from its mounting bracket.
- Install — Mount the new transformer, reconnect primary and secondary leads exactly per your photo.
- Test — Restore power and confirm 24V across the secondary and a normal call for heat.
Signs You Need a Replacement
- Blank thermostat and no 24V power at the control board.
- Furnace does not respond to a call for heat.
- Audible buzzing or burnt smell from the control compartment.
- Repeated blown low-voltage fuses or no secondary output on a multimeter.
Shipping & Returns
Ships same day before 3 PM CST. 30-day returns. Backed by the National HVAC Parts fitment guarantee.
Shipping Information
- Orders placed before 3PM CST ship same business day
- Standard delivery: 2-5 business days
- Express shipping available at checkout
- Free shipping on orders over $75
- Tracking number emailed upon shipment
Return Policy
- 30-day returns on unused parts in original packaging
- Electrical parts (capacitors, contactors, control boards) are final sale once installed
- Email info@nationalhvacparts.com to initiate a return
- Refunds processed within 5-7 business days