Tempstar 40VA Transformer for THB07R25RTA – 277V to 24V with 24V Relays | Ships Today
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Overview
This OEM 40VA control transformer is the factory step-down power source for the Tempstar THB07R25RTA PTAC unit. It converts incoming 277V line power down to the 24V control circuit (OEM 1091226), supplying the relays, thermostat, and contactor coils that operate the system. This listing also covers the unit's companion 24V control relays (OEM 1053004 single relay and 1060940 DPST relay) that switch the cooling and heating loads. When a control transformer fails, the unit goes completely dead on the low-voltage side — no thermostat response, no relay pull-in, and no cooling or heating — even though line power is present. A buzzing, overheated, or visibly burned transformer is a clear sign of failure, often caused by a shorted 24V circuit or a seized contactor coil.
Specifications
| Spec | Value |
|---|---|
| OEM Part Numbers | 1091226 (Transformer), 1053004 & 1060940 (Relays) |
| Type | Control Transformer, Step-Down |
| Brand | Tempstar / Heil / ICP |
| Rating | 40VA |
| Primary Voltage | 277V |
| Secondary Voltage | 24V |
| Application | PTAC Control Circuit |
| Fit | OEM Direct Replacement |
Compatibility
Direct-fit replacement for the Tempstar THB07R25RTA PTAC and other ICP/Heil 277V PTAC units using the same 40VA control transformer. Confirm primary voltage (277V) and VA rating against your existing unit before ordering.
Installation Guide
- Safety First – Disconnect power at the breaker and verify zero voltage with a multimeter on both line and control sides.
- Access – Remove the front grille and control panel to reach the transformer and relay block.
- Document – Photograph all primary and secondary wire connections before disconnecting.
- Remove – Disconnect the 277V primary leads and 24V secondary leads, then unbolt the failed transformer.
- Install – Mount the new transformer, reconnect primary and secondary per your photo, and verify relay wiring.
- Test – Restore power and confirm 24V across the secondary and proper relay pull-in.
Signs You Need a Replacement
- No 24V output on the secondary while 277V is present on the primary
- Transformer is buzzing, hot, swollen, or smells burned
- Thermostat and relays are completely unresponsive
- Blown low-voltage fuse or repeated control-circuit failures
Shipping & Returns
Ships same day before 3 PM CST. 30-day 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