Tempstar 40VA Transformer for THB09K34RTA — 208/240V to 24V OEM | Ships Today

Overview

This is a genuine OEM 40VA control transformer assembly for the Tempstar THB09K34RTA PTAC unit, supplied with its associated 24V relays. The transformer (OEM part 1056899) steps line voltage of 208/240V down to the 24V control voltage that powers the thermostat, relays, and contactor circuit. It is paired here with a 24V relay (1053004) and a 24V DPST relay (1060940) that switch the unit's heating and cooling loads. When a transformer fails — typically from a shorted secondary or overload — the entire low-voltage control circuit goes dead and the unit will not respond to any command, even though line power is present.

Specifications

Compatibility

This 40VA transformer and relay set is the factory-specified control-power components for the Tempstar/Heil/ICP THB09K34RTA PTAC model and installs as a direct OEM replacement.

Installation Guide

1. Safety First — Disconnect power at the unit and breaker, then verify zero voltage with a multimeter.
2. Access — Remove the PTAC front cover and electrical control panel.
3. Document — Photograph all primary and secondary wire connections before disconnecting.
4. Remove — Disconnect the transformer leads, note primary tap selection, and unbolt the transformer and relays from the chassis.
5. Install — Mount the new transformer and relays, matching the correct primary voltage tap, and reconnect wiring per your photo.
6. Test — Restore power and confirm 24V at the secondary and proper relay operation.

Signs You Need a Replacement

• Entire low-voltage control circuit is dead with line power present.
• No 24V reading at the transformer secondary terminals.
• Visible scorching, melted housing, or a burnt smell.
• Relays chatter, fail to pull in, or will not energize.

Shipping & Returns

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