Description
The Honeywell ST9120U1.2 is a universal electronic fan timer / control board designed for gas warm air furnaces and HVAC systems. It integrates the control of combustion blower and circulating fan operations, acting as the central control point for key furnace electrical components. It monitors thermostat heat/cool/fan signals and operates the blower, inducer, and circulating fan accordingly, with adjustable fan-on/fan-off delay settings for heat and cool cycles.
Key Features
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Manufacturer: Honeywell
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Part Number: ST9120U1.2
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Product Type: Furnace fan timer / control circuit board
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Application: Gas warm air furnace and HVAC blower control
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Function: Controls blower and inducer motors based on thermostat demands and safety inputs
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Adjustable Delays: Field-adjustable heat and cool fan-on/off delays
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Optional Terminals: Electronic air cleaner (EAC) and humidifier (HUM) connections
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Voltage: 120 VAC supply (board generally integrates with 24 VAC controls and line power)
Technical Overview
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Integrates control of combustion blower and circulating fan functions in HVAC systems.
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Includes adjustable timing features for heat fan on/off and cool fan on/off delays, enhancing comfort and system response.
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Acts as the central wiring point for most furnace electrical components — making it a core part of fan control logic.
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Often used as a replacement for legacy boards such as ST9101, ST9120, ST9141, and ST9160 families in many gas furnace models.
