Tempstar 40VA Transformer for T8MPV100J20C1 — 115V to 24V | Ships Today

Overview

This is the OEM 40VA control transformer (part 1172810) for the Tempstar T8MPV100J20C1 gas furnace. It steps the incoming 115V line voltage down to the 24V low-voltage power that runs the control board, thermostat, gas valve, and relays. When a transformer fails — often from a shorted thermostat wire or a stuck contactor pulling too much current — the entire 24V control circuit goes dead and the furnace will not respond to a call for heat. A blown internal fuse or a burnt-smelling, discolored transformer body are common signs.

Specifications

Compatibility

Fits the Tempstar T8MPV100J20C1 furnace and shared ICP/Heil platform models using a 40VA 115V-to-24V transformer. Verify the original part number before installing.

Installation Guide

1. Safety First — Disconnect power and verify zero voltage with a multimeter.
2. Access — Remove the control-compartment service panel.
3. Document — Photo all primary and secondary leads before disconnecting.
4. Remove — Label and disconnect the wires, then unbolt the old transformer from its mounting bracket.
5. Install — Mount the new transformer and reconnect primary (115V) and secondary (24V) leads per your photo.
6. Test — Restore power and confirm 24V across the secondary, then run a heat cycle.

Signs You Need a Replacement

• No 24V power — furnace completely unresponsive to the thermostat
• Burnt smell or discolored transformer housing
• Repeated blown low-voltage fuse on the control board
• Measured secondary voltage well below 24V

Shipping & Returns

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