Tempstar 40VA Transformer for T8MPN050B12B1 — 115V to 24V | Ships Today

Overview

This genuine Tempstar OEM 40VA control transformer (part 1172810, "TRANS 115>24 40VA") steps 115-volt line power down to the 24-volt control voltage that runs the thermostat, gas valve, ignition control, and relays on the T8MPN050B12B1 furnace. When a transformer fails — usually from a shorted control circuit or age — the entire low-voltage side goes dead: the thermostat screen blanks, the furnace won't fire, and nothing on the control board responds. A 40VA rating supplies ample power for a standard furnace control circuit.

Specifications

Compatibility

Fits the Tempstar T8MPN050B12B1 gas furnace and related ICP/Heil/Tempstar/Comfortmaker models that use a 115V-to-24V 40VA control transformer. Confirm primary and secondary voltages and lead/terminal configuration against your original part.

Installation Guide

1. Safety First — Disconnect power at the furnace switch and breaker, then verify zero voltage at the transformer leads with a multimeter.
2. Access — Remove the furnace control-compartment service panel.
3. Document — Photograph every primary (line) and secondary (24V) wire connection before disconnecting.
4. Remove — Disconnect the leads, remove the transformer mounting screws, and lift out the old transformer.
5. Install — Mount the new transformer, then reconnect 115V primary and 24V secondary wires exactly per your photo.
6. Test — Restore power and confirm 24V at the secondary and a normal thermostat call/ignition sequence.

Signs You Need a Replacement

• No 24V control power — blank thermostat, furnace won't start
• Repeatedly blown low-voltage fuse on the control board
• Burnt smell or visible scorching on the transformer
• No voltage at the secondary with 115V present at the primary

Shipping & Returns

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