Carrier HK35AA008 Circuit Board

The Carrier HK35AA008 Fan Timer Circuit Board is an OEM replacement control board specifically engineered for 230V control circuits in high-capacity Carrier, Bryant, and Payne units. Designed to replace aging HK35AA004 and electro-mechanical timers like the Paragon HK25AZ070, this multifunction electronic timer features updated microprocessor logic to resolve "lock-out" issues caused by momentary power interruptions of less than 50 milliseconds. It is a critical component for managing fan delay-off timings and coordinating compressor functions in 38AH condensing units and 48MA/50ME multi-zone rooftop units. This board ensures proper air circulation and HVAC system protection by preventing rapid cycling and managing pressure equalization through the low-pressure switch (LPS) circuit. For contractors performing a furnace control board replacement, the HK35AA008 maintains identical wiring connection points to legacy versions, allowing for a seamless drop-in installation without necessitating complex field modifications or harness changes.

• Enhanced Reliability: Advanced circuitry compensates for power flickers, preventing nuisance service calls related to system lock-outs.
• OEM Compatibility: Precision-engineered for Carrier 38AH, 48MA, and 50ME series, ensuring full communication with existing safety strings and contactors.
• Drop-in Replacement: Directly replaces HK35AA004 and BRD-3919 with no changes required to application wiring or terminal locations.
• Optimized Airflow: Precision fan timer circuit management improves indoor air quality and system efficiency by controlling fan run-time post-cycle.
• Integrated Troubleshooting: Digital logic monitoring helps identify low refrigerant levels by recognizing open LPS contacts during the startup sequence.

Can I use the HK35AA008 to replace an old mechanical timer?
Yes. This electronic board is the designated replacement for older electro-mechanical models like the HK25AZ070. Note that the "M" terminal wiring may vary slightly depending on the specific schematic; always refer to the 99TA509591B instruction sheet for precise mapping.

What is the difference between the HK35AA008 and HK35AA009?
The HK35AA008 is strictly for 230V control circuits (typically 60Hz units), while the HK35AA009 is designed for 115V control circuits. Verify your transformer output before installation to prevent board failure.

Does this board require a separate time delay relay?
In some single-pump-out applications where pressures have not equalized, installing a TDU2180C3A delay relay across the LPS is recommended to prevent relay chatter, as the HK35AA008 uses high-sensitivity microprocessor hardware.

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Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.