Tempstar 40VA Transformer for T9MPV125L20D1 — 115V to 24V | Ships Today

Overview

This OEM control transformer, part number 1172810, steps the incoming 115V line voltage down to the 24V control voltage that powers the thermostat, gas valve, control board, and relays in the Tempstar T9MPV125L20D1 furnace. Rated at 40VA, it supplies the low-voltage circuit that every safety and operating control depends on. When a transformer fails — usually from a shorted control wire, a stuck contactor, or simple age — the entire furnace goes dead: no thermostat display, no ignition sequence, and no blower. A blown internal fuse link or a burnt smell at the transformer are common tells.

Specifications

Compatibility

Designed for the Tempstar T9MPV125L20D1 two-stage gas furnace and the broader ICP / Heil / Comfortmaker lineup that uses the 1172810 40VA transformer. Confirm the primary/secondary voltage and VA rating against your existing unit before ordering.

Installation Guide

1. Safety First — Disconnect power at the furnace switch and breaker and verify zero voltage with a multimeter.
2. Access — Remove the control-compartment service panel.
3. Document — Photograph every primary and secondary lead before disconnecting.
4. Remove — Disconnect the line-voltage and 24V leads, then remove the transformer mounting screws.
5. Install — Mount the new transformer, then reconnect the primary (115V) and secondary (24V) leads exactly as photographed.
6. Test — Restore power and confirm 24V across the secondary terminals and normal furnace startup.

Signs You Need a Replacement

• Furnace is completely dead with no thermostat power.
• No 24V output measured across the secondary terminals.
• Burnt smell or discoloration at the transformer.
• Repeated control-circuit failures after a wiring short.

Shipping & Returns

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