Tempstar 40VA Transformer for THB09R25RTA — 277V to 24V Control | Ships Today

Overview

This OEM 40VA control transformer steps 277V line power down to the 24V the control circuit needs on the Tempstar THB09R25RTA. The primary part (OEM 1091226, TRANS 277>24 40VA) powers the thermostat, relays, and contactor coils; the kit also covers the 24V control relays used in this circuit (OEM 1053004 SPST and 1060940 DPST). A failed transformer is one of the most common no-power, no-response faults — when it opens, the unit goes completely dead even though line voltage is present. Replacing it with the factory 40VA part restores reliable 24V control.

Specifications

Compatibility

Direct-fit replacement for the Tempstar THB09R25RTA. The 277V-to-24V 40VA transformer and matching 24V relays are common across Heil, ICP, and Comfortmaker equipment running on 277V control. Confirm both your primary voltage (277V) and VA rating before installing.

Installation Guide

1. Safety First — Disconnect power and verify zero voltage with a multimeter; 277V is lethal.
2. Access — Remove the service panel to expose the control compartment.
3. Document — Photograph every primary and secondary lead before disconnecting.
4. Remove — Disconnect the 277V primary and 24V secondary leads, then unbolt the transformer.
5. Install — Mount the new transformer, land the 277V primary and 24V secondary per your photo.
6. Test — Restore power and confirm 24V across the secondary and proper control operation.

Signs You Need a Replacement

• Unit completely dead with confirmed line voltage present.
• No 24V reading across the transformer secondary.
• Burnt smell or visibly scorched/discolored transformer body.
• Repeated control fuse blowing or intermittent control dropout.

Shipping & Returns

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