Tempstar Transformer for T8MPN075B12B1 — 40VA 115V to 24V | Ships Today

Overview

This is a genuine OEM 40VA control transformer (part number 1172810) for the Tempstar T8MPN075B12B1 gas furnace. The transformer steps down incoming 115V line voltage to the 24V low-voltage control circuit that powers the thermostat, gas valve, igniter circuit, and control board relays. A 40VA rating provides the amperage headroom needed to drive multiple 24V loads simultaneously. When a transformer fails — typically from a shorted secondary, an overloaded control circuit, or simple age — the entire furnace goes dead: no thermostat response, no ignition sequence, and no blower. Replacing the transformer with the correct OEM part restores reliable control power without guesswork on wiring or VA sizing.

Specifications

Compatibility

Designed as the factory transformer for the Tempstar T8MPN075B12B1 furnace and used across related ICP/Heil/Tempstar single-stage gas furnace platforms that share the same 40VA, 115-to-24V control architecture. Always verify 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 with a multimeter at the transformer terminals.
2. Access — Remove the furnace control/blower compartment 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 mounting bracket.
5. Install — Mount the new transformer, reconnect the 115V primary and 24V secondary leads per your photo, and confirm tight terminals.
6. Test — Restore power, measure 24V across the secondary, and run a full heating cycle to confirm ignition and blower operation.

Signs You Need a Replacement

• Furnace is completely unresponsive — no thermostat display or call for heat.
• Repeatedly blown low-voltage fuse on the control board.
• No measurable 24V across the transformer secondary while line voltage is present.
• Buzzing, scorched smell, or visible discoloration on the transformer body.

Shipping & Returns

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