Tempstar 40VA Transformer for T8MPL100J20A1 — 115V to 24V Control | Ships Today

Overview

This OEM control transformer (part #1012722) is the low-voltage power supply for your Tempstar T8MPL100J20A1 gas furnace. It steps line voltage of 115V down to the 24V required to run the thermostat, gas valve, igniter circuit, and control board. Rated at 40VA, it delivers enough current to drive every 24V accessory on the furnace at once. When a transformer fails, the entire low-voltage control system goes dead: the thermostat screen goes blank, the furnace will not respond to a call for heat, and you may smell burnt insulation or see scorch marks on the windings. A buzzing or humming transformer that still works is on its way out and should be replaced before it strands you on a cold night.

Specifications

Compatibility

Engineered as a direct OEM fit for the Tempstar T8MPL100J20A1 furnace and shared across many ICP-built Tempstar, Heil, Comfortmaker, and Arcoaire 115V-to-24V 40VA platforms. Always confirm your existing transformer reads 115V primary and 24V secondary at 40VA before installing.

Installation Guide

1. Safety First — Disconnect power at the furnace switch and breaker, then verify zero voltage at the primary leads with a multimeter.
2. Access — Remove the furnace blower-compartment service panel to expose the control area.
3. Document — Photograph all primary and secondary wire connections before disconnecting anything.
4. Remove — Label and disconnect the primary (line) and secondary (24V) leads, then unbolt the transformer from its mounting bracket.
5. Install — Mount the new transformer, reconnect the primary and secondary leads exactly per your photo, and secure all spade or wire-nut connections.
6. Test — Restore power and confirm 24V across the secondary, then trigger a call for heat to verify normal operation.

Signs You Need a Replacement

• Blank thermostat and completely dead low-voltage controls.
• Burnt smell, discoloration, or melted potting on the transformer body.
• No 24V reading at the secondary while 115V is present at the primary.
• Audible buzzing or humming and a repeatedly blown low-voltage fuse.

Shipping & Returns

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