Tempstar 40VA Transformer for T9MPV100J20D1 — 115V to 24V | Ships Today
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Overview
This OEM 40VA control transformer (part number 1172810, "TRANS 115>24 40VA") provides the 24V low-voltage power for the Tempstar T9MPV100J20D1 two-stage gas furnace. It transforms the 115V incoming line voltage down to the 24V control signal that operates the thermostat circuit, two-stage gas valve, ignition control, and blower commands. A failed transformer — commonly caused by a short in the thermostat wiring or an overloaded control circuit — kills all low-voltage power, leaving the furnace completely unresponsive. Installing a fresh 40VA transformer restores control power and returns the system to normal operation.
Specifications
| Spec | Value |
|---|---|
| Part Number | 1172810 |
| Type | Control / Step-Down Transformer |
| Brand | Tempstar (ICP / Heil family) |
| Rating | 40 VA |
| Primary Voltage | 115V |
| Secondary Voltage | 24V |
| Fit | OEM direct replacement |
Compatibility
Direct-fit replacement for the Tempstar T9MPV100J20D1 two-stage gas furnace and shared ICP, Heil, and Comfortmaker furnace platforms. The 40VA 115V-to-24V control transformer is a widely used component across these models. Confirm your existing part number is 1172810 and your primary voltage is 115V before installing.
Installation Guide
- Safety First — Disconnect furnace power at the breaker and verify zero voltage at the transformer leads with a multimeter.
- Access — Remove the control-compartment service panel.
- Document — Photograph all primary and secondary wire connections before disconnecting.
- Remove — Label and disconnect the leads, then unbolt the old transformer from its bracket.
- Install — Mount the new transformer and reconnect the 115V primary and 24V secondary leads exactly as photographed.
- Test — Restore power, confirm ~24V across the secondary, and verify the thermostat, ignition, and blower all operate.
Signs You Need a Replacement
- Furnace is completely dead with no thermostat response.
- No 24V output measured at the transformer secondary.
- Control-board low-voltage fuse repeatedly blows.
- Burnt odor or visibly scorched transformer body.
Shipping & Returns
Ships same day on orders placed before 3 PM CST. 30-day hassle-free returns. Backed by the National HVAC Parts fitment guarantee.
Shipping Information
- Orders placed before 3PM CST ship same business day
- Standard delivery: 2-5 business days
- Express shipping available at checkout
- Free shipping on orders over $75
- Tracking number emailed upon shipment
Return Policy
- 30-day returns on unused parts in original packaging
- Electrical parts (capacitors, contactors, control boards) are final sale once installed
- Email info@nationalhvacparts.com to initiate a return
- Refunds processed within 5-7 business days