Tempstar Transformer for T9UHX100L20A2 — 40VA 115V to 24V | Ships Today

Overview

This OEM control transformer (part #1172810) steps 115 volts down to the 24-volt control voltage that runs the thermostat, gas valve, and control board in your Tempstar T9UHX100L20A2 furnace. Rated at 40VA, it supplies the low-voltage circuit that ties the entire heating and cooling control system together. When a transformer fails — usually from a shorted low-voltage wire, a stuck contactor, or simple age — the furnace goes completely dead with no thermostat display and no response to a heat or cool call. A blown transformer often accompanies a shorted thermostat wire, so inspect the 24V wiring before replacing.

Specifications

Compatibility

Direct OEM replacement for the Tempstar T9UHX100L20A2 furnace and matching ICP/Heil/Comfortmaker boards that use a 40VA 115-to-24V control transformer. Verify the VA rating and primary/secondary voltages on your old transformer before installing.

Installation Guide

1. Safety First — Disconnect power to the furnace and verify zero voltage with a multimeter.
2. Access — Remove the furnace service panel to reach the control box.
3. Document — Photograph the primary (line) and secondary (24V) wire connections before disconnecting.
4. Remove — Disconnect the primary and secondary leads and unbolt the transformer from its mounting tab.
5. Install — Mount the new transformer and reconnect the 115V primary and 24V secondary leads per your photo.
6. Test — Restore power and confirm 24 VAC at the secondary and a live thermostat.

Signs You Need a Replacement

• Furnace completely dead with a blank thermostat
• No 24V reading at the secondary terminals
• Burnt smell or visibly charred transformer windings
• Repeated blown low-voltage fuses

Shipping & Returns

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