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Tech Note ©
October 2013
Honeywell Air Flow Switch (AFS)
Air Flow Switch Operation
The air flow switch (AFS) senses differential pressure across its inputs. The AFS signals the air cleaner ON when a vacuum
is present at the unit. Removing the tubing and using a straw to apply a vacuum near the orifice will turn the AFS ON.
Also blowing air into the unconnected input will activate the AFS.
This test will bypass the airflow switch allowing the power supply to operate. If the indicator light does not turn on with
the airflow switch bypassed, then this indicates a problem with the power supply. Note the collector cells should be
removed to insure the output is not being shorted.
Honeywell manufactured two AFS versions. The new version has a smaller circuit board. Zoom in to the photos to
determine your version.
Air Flow Switch Bypass Procedure
1. Bypass the AFS:
• (2012 - Present) Unplug the AFS then connect the two pins marked "bypass AFS" using a jumper wire.
• (Prior - 2012) Short the resistor to ground with a jumper wire, see photo for your model
2. The door interlock switch must be ON
3. Turn ON the On-Off switch
F300 F50 F52 Models ................................................................................................................. 2012 - Present
On the power supply, connect the two pins labeled "Bypass AFS" located on J3 with a jumper. To permanently bypass the
AFS cut the R16 jumper/resistor.
Bel-Aire ElectronicAirCleaners.com, Inc · 70 Case Avenue Seekonk MA 02771 · Ph: 774.901.4770
R16
ElectronicAirCleaners.com
ElectronicAirCleaners.com
J3
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Table of Contents
Related Manuals for Honeywell F50
Summarization of Contents
Air Flow Switch Operation
AFS Functionality
The AFS senses differential pressure, signaling the air cleaner ON when a vacuum is present.
Air Flow Switch Bypass Procedure
General Bypass Steps
Bypass the AFS, ensure door interlock is ON, then turn the On-Off switch ON to test power supply.
Bypass for F300 F50 F52 Models (2012-Present)
Connect the two pins marked 'Bypass AFS' on J3 using a jumper wire. Cut R16 for permanent bypass.
Model-Specific Bypass Procedures
Bypass for F300 F52F Models (2006-2012)
Ground the power supply resistor J8. A paint coating may need to be cleaned.
Bypass for F300 F50F F50E F52 Models (1990-2006)
Permanently disabling the AFS is outlined in the Honeywell F300 Product Data Manual.
Technical Specifications and Notes
Bypass Procedure Note (1990-2006)
The 1990-2006 bypass lights neon indicator, powers supply, but does not fool W8600F remote indicator.
Air Flow Switch Voltages
Measured voltages for Black, Gray, Orange, and Violet wires in OFF and ON states.
Dimensions of 4074ETH
Details the mounting holes and overall size of the 4074ETH unit.
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