Tempstar 40VA Transformer 115V to 24V for T9UHX100L20A1 — OEM 1172810 | Ships Today

Overview

This OEM control transformer (Tempstar part #1172810) steps the 115V line voltage in your Tempstar T9UHX100L20A1 gas furnace down to the 24V needed by the control board, thermostat, gas valve, and safety circuits. Rated at 40VA, it supplies the low-voltage power that runs the entire control system. When a transformer fails, the furnace goes completely dead on the low-voltage side — no thermostat display, no call for heat, and no 24V at the control board. A blown transformer is often the downstream symptom of a shorted control or a wiring fault, so inspect the circuit before replacing.

Specifications

Compatibility

Built for the Tempstar T9UHX100L20A1 9-series gas furnace and used across many Heil, ICP, and Comfortmaker furnace models that call for OEM 40VA transformer 1172810. Verify your primary/secondary voltages and VA rating against the existing unit.

Installation Guide

1. Safety First — Disconnect power at the furnace switch and breaker, then verify 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, unscrew the transformer from its mounting bracket, and lift it out.
5. Install — Mount the new transformer, then reconnect primary and secondary leads exactly per your photo.
6. Test — Restore power and confirm 24V across the secondary terminals and a normal call for heat.

Signs You Need a Replacement

• No 24V at the control board or thermostat
• Furnace completely unresponsive to a call for heat
• Blank thermostat with line voltage present at the furnace
• Burnt smell or discoloration on the transformer windings

Shipping & Returns

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