Tempstar 40VA Transformer for T9MPD075F12A3 — 115V to 24V Control Transformer | Ships Today

Overview

This is the OEM control transformer (OEM #1012722, "TRANS 115>24 40VA") for the Tempstar T9MPD075F12A3 gas furnace. The transformer steps the incoming 115V line voltage down to the 24V low-voltage control circuit that powers the thermostat, control board logic, gas valve, and relays. Rated at 40VA, it supplies enough current for the furnace's controls plus a typical thermostat and accessory load. When a transformer fails — usually from a shorted secondary, a stuck contactor pulling excess current, or simple age — the entire 24V control system goes dead: the thermostat screen blanks, nothing energizes, and the furnace appears completely unresponsive even though line power is present. A blown transformer is also frequently a symptom of a downstream short, so inspect the low-voltage wiring before energizing the replacement.

Specifications

Compatibility

Built for the Tempstar T9MPD075F12A3 furnace and used across ICP-family equipment (Tempstar, Heil, Comfortmaker) that specifies the 1012722 40VA 115/24 transformer. Verify primary voltage and VA against your unit before installing.

Installation Guide

1. Safety First — Disconnect furnace power at the breaker and confirm zero voltage with a multimeter.
2. Access — Remove the control-compartment service panel.
3. Document — Photograph the primary (line) and secondary (24V) wire connections before disconnecting.
4. Remove — Disconnect the leads, remove the mounting screw or bracket, and take out the failed transformer.
5. Install — Mount the new transformer, land the 115V primary and 24V secondary leads exactly per your photo, and confirm tight connections.
6. Test — Restore power and verify 24V across the secondary; confirm the thermostat powers up and the furnace sequences normally.

Signs You Need a Replacement

• Thermostat is blank and the furnace is completely dead despite line power.
• No 24V reading at the control board or thermostat terminals.
• Transformer is hot, buzzing, or shows scorch marks.
• Furnace works intermittently then loses all control power.

Shipping & Returns

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