Tempstar 40VA Transformer for T8DNL075B12A1 – 115V to 24V Furnace Transformer | Ships Today

Overview

This genuine OEM 40VA control transformer (part #1012722) for the Tempstar T8DNL075B12A1 furnace steps the incoming 115V line voltage down to the 24V control voltage that powers the thermostat, gas valve, igniter control, and relays. The 40VA rating supplies enough current to drive the furnace's low-voltage control circuit plus a connected thermostat or zone board. When a transformer fails, the entire 24V control system goes dead — the thermostat screen blanks, the furnace won't fire, and nothing on the control board energizes. A buzzing, scorched, or open-winding transformer is a common cause of a furnace that has line power but no response.

Specifications

Compatibility

Fits the Tempstar T8DNL075B12A1 gas furnace and other ICP-family models (Heil, Comfortmaker, Arcoaire) using a 115V-to-24V 40VA control transformer. Confirm primary voltage and VA rating on the existing unit before ordering.

Installation Guide

1. Safety First – Disconnect power at the breaker and verify zero voltage with a multimeter.
2. Access – Remove the furnace control/blower panel to reach the transformer.
3. Document – Photograph all primary and secondary wire connections before disconnecting.
4. Remove – Disconnect the leads, remove the mounting screws, and lift out the failed transformer.
5. Install – Mount the new transformer and reconnect the 115V primary and 24V secondary leads exactly per your photo.
6. Test – Restore power and confirm 24V at the secondary and a normal thermostat call.

Signs You Need a Replacement

• Blank thermostat and a dead 24V control circuit
• Furnace has line power but will not fire or respond
• Buzzing, humming, or burnt smell from the transformer
• No measurable 24V across the secondary terminals

Shipping & Returns

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