Honeywell 4074ETJ
Airflow Switch for Honeywell F300 F50F Single Cell Models
Price:$41.00
  Series Two
1998 - Present
Series One
1993-97

Air Flow Switch for model F50F F300A F300B. Only for use with models having one collector cell. Black plastic case measures approx 3½" square, wire length 7". Includes 7" of clear ¼" OD tubing.

This AFS has the 4 individual pins. Honeywell does not offer a replacement AFS with the plug connector for the single cell models. Replaces 202121C.

Used in the highlighted models:

12½ x 20 16 x 20 16 x 25 20 x 20 20 x 25
F300A2012 F300E1001 F300E1019 F300E1027 F300E1035
F300B2012 F300A1620 F300A1625 F300A2020 F300A2025
F50F1040 F50F1149 F50F1073 F50F1032 F50F1065

Air Flow Sensor - 3 Variations

Honeywell 4074EZB
4074EZB
1998 - Present
AFS Plug Type Connection
PLUG Type Connection
Honeywell 4074ETH
4074ETH
1993 - 1997
AFS Pin Type Connection
PIN Type Connection

There are 3 different air flow sensor part numbers. The 3 variations are the same except for the connector type, wire length, and length of clear tubing included.

4074EZB (plug connector):
√ All F300 series 
√ F50F F52F F58F series two 1998 to present

4074ETH (4 pin connectors):
√ F50F F52F F58F series one 1993 to 1997

4074EHJ (4 pin connectors and shorter wires)
√ F50F series one (single cell model only)

In 1998 Honeywell introduced the series 2 that simplified connections with modular plugs. The AFS was redesigned with a modular plug. The power supply was redesigned with both a plug connector and the pin connectors for backward compatibility.

The F300 and F50F series 2 are manufactured using the plug connector AFS. But some Honeywell manuals will list the pin connector AFS as the replacement. This is to reduce distributor inventory, we don't settle for less.

The pin connector AFS will connect to all power supplies. The plug connector AFS will only connect to power supplies after 1998. To eliminate cross wring problems use the plug connector AFS if your power supply is equipped with the plug connector.

If you are replacing the power supply and AFS, you should use the AFS with the plug connector. Also use the plug connector AFS if your power supply has been replaced after 1998. The TechNote below shows a photo of the compatible power supply.

The 4074EHJ is only used in the single cell F300 F50F model. This AFS has pin connectors and shorter wires. The 4074EHJ comes with 7" of 1/4" OD tubing.Same power Supply with diferent AFS Connector

Test Procedure for New AFS

AFS RevisedThe AFS internal electronics were revised in 2006 to utilize surface mount technology. Functionally the AFS is the same and the part number remains the same. The new version is fully interchangeable with the old.

The new AFS does not have the test resistor that when grounded would turn on the power supply. This was a test procedure outline in the F50F manual. This would bypass the AFS functionality and force on the power supply. The test would show if the power supply was not working because the AFS was not working.

To force on the power supply and bypass the AFS, ground the jumper resistor on the power supply J8. To permanently bypass the AFS, cut the J8 jumper. Photo below shows grounding J8 to force on the power supply. The other end of our red patch jumper is connected to the chassis.

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