Tempstar 40VA Transformer & Relay Kit for THB09K50RTA — 208/240V to 24V | Ships Today

Overview

This OEM control kit for the Tempstar THB09K50RTA PTAC includes the 40VA step-down transformer (OEM 1056899, 208/240V primary to 24V secondary) plus the 24V control relays (OEM 1053004 single relay and OEM 1060940 DPST relay). The transformer is the heart of the low-voltage control circuit — it powers the thermostat, relays, and contactor coil at 24V. When a transformer fails (open winding, short, or burnout from a shorted coil downstream), the entire control circuit goes dead and the unit will not start in heat or cool even though line power is present. Replacing it with the correct 40VA OEM transformer restores 24V control power.

Specifications

Compatibility

Direct OEM fit for the Tempstar/Heil/ICP THB09K50RTA PTAC low-voltage control circuit. The 40VA rating and 208/240V-to-24V configuration match the factory specification. Confirm your model and serial tag before ordering.

Installation Guide

1. Safety First — Disconnect power at the PTAC plug or breaker and verify zero voltage with a multimeter.
2. Access — Remove the service panel to reach the control box.
3. Document — Photograph all primary and secondary wire connections before disconnecting.
4. Remove — Unbolt the transformer mounting bracket and disconnect the line-voltage primary and 24V secondary leads.
5. Install — Mount the new transformer, land the primary on 208/240V and the secondary on the 24V circuit per your photo.
6. Test — Restore power and verify 24V across the secondary; confirm the unit energizes in heat and cool.

Signs You Need a Replacement

• No 24V control power — unit completely unresponsive though line voltage is present.
• Blown low-voltage fuse or repeated control failures.
• Burnt smell or visibly scorched transformer housing.
• Contactor and relays won't pull in on a call for heat or cool.

Shipping & Returns

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