ST9120U1003
Universal Electronic
Fan Timer
Training Module
ST9120U - What You Will Learn:
• Product Overview
• Set Up
• Installation
• Troubleshooting
• Product Cross Reference
• ST9120 Advantage
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What is the ST9120U Electronic Fan Timer?
• A universal electronic fan timer that
integrates control of all combustion
blower and circulating fan operations
in a gas warm air appliance
- Monitors the thermostat for heat, cool
and fan demands.
- Runs the induced draft blower motor
and runs the circulating fan (up to two
speeds) as needed.
- Monitors limit switch strings and
energizes ignition control.
- Central wiring point for the electrical
components of the furnace. Saves time!
One part number:
ST9120U1003
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ST9120U Electronic Fan Timer Features
• Why choose the Honeywell ST9120U?
• Universal application
• Replaces over 25 existing Honeywell controls
• Easy installation
• DIP switch selectable circulating fan delays
• Heat on/off delay
• Cool on/off delay (cool off fixed at 30 seconds)
 Single model services multiple furnace
applications
 Included with the ST9120U:
• Wiring information and adapter for the ST9101
• Original appliance application
• Delay timing recommendation
• Quality construction for a long service life
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Installation
Installation of the ST9120U
• Location and Mounting
- Mount the ST9120U Electronic Fan Timer in the appliance wiring
compartment or furnace vestibule
- Mounting screws provided
• Wiring
- Make sure that all wiring complies with local codes and
ordinances.
- Disconnect power before making wiring connections.
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Set-Up
Set up of the ST9120U
• Setting DIP switches
- Heat fan-on delay
 On: 30/60 Seconds
 Starts timing when main valve energized
- Heat fan-off delay
 Off: 60/100/140/180 Seconds
 Starts timing when main valve is de-energized
- Cool fan-on delay
 On: 4/30 Seconds
 Starts with call for cooling
- Cool fan-off delay fixed at 30 seconds
- Post Purge: 5 seconds
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Set up of the ST9120U
Recommended
dip switch
settings are
included in the
installation
instructions as
well as the
Honeywell
Residential
Combustion
Application and
Selection
Guide.
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Troubleshooting
Troubleshooting of the ST9120U
• Look for appropriate voltages at the ST9120U
terminals
• Check operation and timing of:
- Combustion blower
- Fan at heating speed
- Fan at cooling speed
• Check limit operation and system response
Note: The ST9120U schematics show internal switching to clarify operation
and assist in troubleshooting.
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Product Cross Reference
Product Cross Reference
The ST9120U replaces over 25 existing Honeywell
controls:
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ST9101A1006
ST9120C1020
ST9120C4016
ST9120G2016
ST9101A1014
ST9120C2002
ST9120C4040
ST9120G2024
ST9101A1022
ST9120C2010
ST9120C4057
ST9120G2032
ST9120A1006
ST9120C2028
ST9120C5005
ST9120G4004
ST9120A2004
ST9120C3000
ST9120C5013
ST9120G4012
ST9120B1005
ST9120C3018
ST9120D3009
ST9120G4038
ST9120C1012
ST9120C4008
ST9120G2008
Product Cross Reference
• Where do I find Honeywell universal fan timer cross
reference information?
- www.customer.honeywell.com
- Honeywell Application Selection and Cross
Reference Guide – Form 63-9575
- Honeywell Laminated Truck Visor – Form 63-9581
- Honeywell Residential Technical Support: 1-800-468-1502
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www.customer.honeywell.com
• See Cross Reference Search box in right column.
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ST9120U Advantage
• When promoting the ST9120U keep these
advantages in mind:
- The ST9120U universal control replaces over 25 existing
Honeywell controls. This in turn, reduces inventory and
saves time looking for the right part.
- A central wiring point for most of the electrical components
of the furnace makes installation easy and gets the installer
on to the next job faster.
- Easy to set selectable heat and cool on/off settings adapt to
the application.
- The ST9120U makes the choice simple; one control saves
time and money, improving your bottom line.
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ST9120U1003
Universal Electronic Fan Timer
Knowledge Test
ST9120U Knowledge Test
• Now that you completed this training module, take the
short quiz to test your knowledge.
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Test
1. The ST9120U Universal Electronic Fan Timer
controls the blower and circulating fan in gas
warm air appliances? T or F
2. The ST9120U is a central wiring point for most of
the electrical components in the furnace? T or F
3. The ST9120U replaces over 25 Honeywell and
competitor controls? T or F
4. The universal electronic fan timer monitors the
thermostat for heat, cool and fan demands? T or F
5. The heat and cool on/off delays are set through
dip switches? T or F
6. Honeywell only has one resource for cross
reference information? T or F
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Answer Key
1.
2.
3.
4.
5.
6.
20
T
T
F
T
T
F