Tempstar 40VA Transformer for T9MPV075F12A3 — 115V to 24V Control Transformer | Ships Today

Overview

This OEM Tempstar control transformer (part number 1012722, "TRANS 115>24 40VA") steps the furnace's 115V line voltage down to the 24V control voltage that powers the thermostat, control board logic, gas valve, and relays on your T9MPV075F12A3. Rated at 40VA, it supplies enough current to drive the furnace's low-voltage circuit plus a typical cooling contactor on the matched air conditioner. When a transformer fails — usually from a shorted thermostat wire, a stuck contactor, or simple age — the entire 24V system goes dead: no thermostat display, no fan, no heat or cool call. A buzzing, overheating, or burnt-smelling transformer is a clear sign of overload or impending failure.

Specifications

Compatibility

Direct-fit replacement for the Tempstar T9MPV075F12A3 gas furnace. The 115V-to-24V 40VA transformer is shared across ICP-family equipment including Heil, Comfortmaker, and Arcoaire furnaces using the same control platform. Verify the primary tap voltage and VA rating against your unit before installing.

Installation Guide

1. Safety First — Cut power at the service disconnect and thermostat. Verify zero voltage at the transformer leads with a multimeter.
2. Access — Remove the furnace control/junction box access panel.
3. Document — Photograph all primary and secondary lead connections before disconnecting.
4. Remove — Disconnect the line-voltage primary leads and the 24V secondary leads, then unbolt the transformer from the chassis.
5. Install — Mount the new transformer, land the 115V primary and 24V secondary leads exactly per your photo, and confirm a solid chassis ground.
6. Test — Restore power and measure ~24V across the secondary. Confirm the thermostat powers up and the furnace responds to a heat call.

Signs You Need a Replacement

• Dead thermostat — no display and no response to calls
• No 24V output measured across the secondary terminals
• Audible buzzing, overheating, or a burnt-electrical smell
• Blown low-voltage fuse that keeps failing after replacement

Shipping & Returns

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