Tempstar 40VA Transformer for T9MVX040F12A1 — 115V to 24V Primary | Ships Today

Overview

This OEM 40VA control transformer (part #1172810) provides low-voltage power to the controls of your Tempstar T9MVX040F12A1 gas furnace, stepping incoming 115V line voltage down to the 24V used by the control board, gas valve, igniter circuit, and thermostat. A failed transformer kills the entire 24V control circuit: the furnace ignores thermostat calls, the control board shows no power, and nothing energizes. Its 40VA rating supplies adequate capacity for the furnace's electronic ignition controls and thermostat load without overheating.

Specifications

Compatibility

Direct OEM fit for the Tempstar T9MVX040F12A1 variable-speed gas furnace. The same 1172810 transformer is used across many ICP-family furnaces sold under the Tempstar, Heil, Comfortmaker, and Arcoaire brands. Confirm the printed part number on your existing transformer before ordering.

Installation Guide

1. Safety First — Disconnect power at the furnace switch and breaker, then verify zero voltage at the transformer terminals with a multimeter.
2. Access — Remove the furnace control/burner service panel.
3. Document — Photograph all primary (line) and secondary (24V) wire connections before disconnecting.
4. Remove — Disconnect the primary and secondary leads, then unbolt the transformer from its bracket.
5. Install — Mount the new transformer and reconnect the 115V primary and 24V secondary leads exactly per your photo.
6. Test — Restore power and confirm 24V at the secondary plus a normal ignition sequence on a thermostat call.

Signs You Need a Replacement

• Furnace completely unresponsive with no 24V control power
• Repeatedly blown low-voltage fuse on the control board
• Buzzing, humming, or burnt smell from the transformer
• Measured 0V or wrong secondary voltage while 115V is present on the primary

Shipping & Returns

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