ICP 40VA Transformer for RGS303HRFA0AAAA — 120/24V Class 2 | Ships Today

Overview

This OEM 40VA control transformer is the low-voltage power source for the ICP / Tempstar / Heil RGS303HRFA0AAAA gas furnace and its associated 24V relays (parts 1183814 and 1178205). The transformer steps 120V line power down to the 24V Class 2 control voltage that runs the thermostat, control board, gas valve, and switching relays. When it fails, the furnace goes completely dead — no thermostat display, no ignition, and no relay actuation. A transformer that hums loudly, runs hot, or has a blown internal fuse should be replaced to restore control power.

Specifications

Compatibility

Fits the ICP / Tempstar / Heil RGS303HRFA0AAAA gas furnace and parts-compatible RGS-series units using 120V primary / 24V secondary control power. Confirm your existing primary voltage tap and VA rating before installing.

Installation Guide

1. Safety First — Disconnect power at the switch and breaker, then verify zero voltage with a multimeter.
2. Access — Remove the furnace control-compartment service panel.
3. Document — Photograph the primary and secondary lead connections before disconnecting.
4. Remove — Disconnect the leads, remove the mounting screws, and take out the failed transformer.
5. Install — Mount the new transformer, wire the 120V primary and 24V secondary exactly per your photos, and confirm correct tap selection.
6. Test — Restore power and verify a steady 24V output and normal furnace operation.

Signs You Need a Replacement

• Furnace is completely dead with no 24V control power.
• Loud humming, overheating, or burnt smell from the transformer.
• Repeatedly blown internal fuse or no secondary voltage reading.
• Thermostat and relays unresponsive despite 120V at the primary.

Shipping & Returns

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