Tempstar 40VA Transformer for T8DNL075F16B1 — 115V to 24V | Ships Today

Overview

This genuine OEM control transformer (part number 1172810, "TRANS 115>24 40VA") supplies low-voltage power to the Tempstar T8DNL075F16B1 gas furnace. It steps the incoming 115V line voltage down to 24V at 40VA, energizing the thermostat circuit, gas valve, control board, and relays. When the transformer fails, the entire low-voltage system goes dead: the thermostat screen blanks, the furnace will not respond to a heat call, and nothing on the 24V circuit operates. A failed transformer is often the result of a shorted gas valve, pinched thermostat wire, or control board fault, so inspect the 24V circuit for shorts before installing the replacement.

Specifications

Compatibility

Fits the Tempstar T8DNL075F16B1 furnace and the broader ICP/Tempstar/Heil T8DNL series that uses a 40VA, 115V-to-24V control transformer. Confirm your existing transformer is rated 40VA before ordering.

Installation Guide

1. Safety First — Disconnect power at the furnace switch and breaker; verify zero voltage with a multimeter on both the 115V and 24V terminals.
2. Access — Remove the control/blower compartment service panel.
3. Document — Photograph all primary (line) and secondary (24V) wire connections before disconnecting.
4. Remove — Disconnect the leads, unfasten the transformer from its mounting bracket, and lift it out.
5. Install — Mount the new transformer and reconnect primary and secondary leads exactly per your photo.
6. Test — Restore power, confirm ~24V across the secondary terminals, and run a heat cycle.

Signs You Need a Replacement

• Blank thermostat / no 24V power anywhere
• Furnace does not respond to a heat call
• No measurable voltage across the secondary terminals
• Transformer is hot, humming loudly, or smells burnt

Shipping & Returns

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