Tempstar 40VA Transformer for T9MPV075F12B1 — 115V to 24V Control | Ships Today

Overview

This is the OEM control transformer (Part Number 1012722) for the Tempstar T9MPV075F12B1 gas furnace. It steps the 115-volt incoming line voltage down to the 24-volt control circuit that powers the thermostat, ignition control board, gas valve, and relays. Rated at 40VA, it supplies the current needed for the full control sequence on this variable-speed furnace. A failed transformer kills the entire low-voltage side — no thermostat display, no call for heat, and no ignition. The usual culprit is a shorted secondary winding caused by an overloaded or pinched control wire, which often blows the board's low-voltage fuse as soon as power returns. Replacing it with the correct OEM 40VA transformer restores reliable 24V control power and protects the ignition board.

Specifications

Compatibility

Built for the Tempstar T9MPV075F12B1 furnace and shared across the ICP/Heil/Comfortmaker family of 9-series variable-speed gas furnaces that use the 1012722 transformer. Verify your existing unit is a 115V-to-24V, 40VA transformer 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 and 24V secondary leads, then unbolt the transformer from its bracket.
5. Install — Mount the new transformer, reconnect primary and secondary leads exactly per your photo, and tighten 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 housing.

Shipping & Returns

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