Tempstar 40VA Transformer for T9MPV075F12D1 — 115V to 24V Control | Ships Today

Overview

This is the OEM control transformer (Part Number 1172810) for the Tempstar T9MPV075F12D1 gas furnace. The transformer steps the incoming 115-volt line voltage down to the 24-volt low-voltage control circuit that powers the thermostat, ignition control board, gas valve, and relays. Rated at 40VA, it supplies enough current to drive the full control sequence on this single-stage variable-speed furnace. When a control transformer fails, the furnace goes completely dead on the low-voltage side: no thermostat display, no call for heat, no blower, and no ignition. A common failure mode is a shorted secondary winding from an overloaded or miswired control circuit, which often blows the board fuse the instant power is restored. Replacing the transformer with the correct OEM 40VA unit restores reliable 24V control power.

Specifications

Compatibility

Engineered for the Tempstar T9MPV075F12D1 furnace and shared across the ICP/Heil/Comfortmaker family of 9-series variable-speed gas furnaces that use the 1172810 transformer. Always confirm your existing transformer is a 115V-to-24V, 40VA unit before installing.

Installation Guide

1. Safety First — Disconnect power at the furnace switch and breaker; verify zero voltage at the transformer primary leads with a multimeter.
2. Access — Remove the furnace control/blower compartment door.
3. Document — Photograph all primary (line) and secondary (24V) wire connections before disconnecting.
4. Remove — Disconnect the line-voltage leads and the 24V secondary leads, then unbolt the transformer from its mounting bracket.
5. Install — Mount the new transformer, reconnect primary and secondary leads exactly per your photo, and secure all terminals.
6. Test — Restore power, confirm 24V across the secondary, and run a full heat cycle to verify ignition and blower operation.

Signs You Need a Replacement

• No power to the thermostat or control board (dead 24V circuit).
• Repeatedly blown low-voltage fuse on the ignition control board.
• No measurable voltage across the transformer secondary with line power present.
• Burnt smell or visible scorching on the transformer body.

Shipping & Returns

Ships same day before 3 PM CST. 30-day returns. Backed by the National HVAC Parts fitment guarantee.