Air Flow Sensor Kit for White-Rodgers SST Series

White-Rodgers Electro-Air Cross Reference

White-Rodgers equipment is identified by a model number. Replacement parts can be ordered based on the model number. Current model numbers are in the format SST1400-151, previous SST model numbers were 14c26s-010. See the Model Number Cross Ref for more examples. With the previous model numbers only the digits before the dash (14c26s) are needed for part lookup.

White-Rodgers parts are identified by a part number or manufacturing code. Often the manufacturing code changes but the part number remains the same. Such would be the case if White-Rodgers made improvements to the part, but the part remained fully interchangeable with the previous version.

White-Rodgers part numbers start with the letter F, such as F811-0398. The manufacturing code starts EAC A, example EAC A811-0395. Sometimes the EAC is omitted and the code starts with just the A. The manufacturing code is often stamped in black ink. If using a manufacturing code. lookup the part number in the A to F Cross Ref, then search our site for the part number.

• Sears Cross Reference
• Model Number Cross-Ref
• Power Box AFS Photos
• A to F Cross Reference

SST Series Air Flow Sensor Option

The newest SST is available with or without a built-in air flow sensor (AFS). The AFS automatically turns on the air cleaner when air flow is present. AKA; air flow switch, air flow monitor.

Newer furnaces provide a power connection for an air cleaner making the air flow switch not necessary. Check the schematic pasted on the inside of your air handler for a connection labeled EAC 120v. When using the EAC connection, wire the EAC contacts to a 120v outlet (in a utility box). Then plug the SST cord in to the outlet. 

Warning do not wire the SST directly to the wires that power the furnace blower. A multi-speed blower can back feed voltage when running on different speeds. Voltage spikes are also a problem. Another option is an external air flow sensor.

Power Supply Compatibility

The current replacement power supply (F858-0475) replaces most previous 120v supplies. This power supply only needs to be connected to 120v and will output 6450 vdc.

This supply will not replace supplies denoted as dual voltage in the cross reference. Dual voltage supplies where used with cells that required two voltages, one for the ionizing wires, and a lower voltage for the collector plates. These supplies are no longer available and such models need to be replaced.

The F858-0475 replaces these previous part numbers:

• F858-0475 Installation
• F858-1002 Installation

Air Flow Sensor Compatibility

The above AFS shows the star that denotes compatibility with the new power supply

Photo above and below show AFS dated 1995 and 1986

If you have an air flow sensor then note that the new power supplies are only compatible with the new air flow sensors. The air flow sensors manufactured after 1998 are more robust than the earlier versions.

Compatible air flow sensors are identified by a printed black star located in the corner. If your AFS does not have this star then it must be upgraded.

When a new power supply is used with an earlier air flow sensor, the power supply will burn-out. The primary winding of the 24v step down transformer will heat up and short out.

The newest power supply was redesigned with a 24v step down transformer at the front end. This eliminated problems with line spikes shorting the switching FET (field effect transistor). But the early AFS had a half-wave rectifier and the transformer requires a full sine wave. The earlier air flow sensor will supply a half sine wave that will burn out the transformer.

The photos of the earlier AFS versions show there are fewer components. Note the new AFS has four diodes (full wave bridge) compared to two.

Simple Power Supply Test Procedure

Troubleshoot Problem:

• The neon indicator light is not coming on
  
• The cells never spark
  
• Power box switch is ON
  
• Door is tight in place
  
• Blower is ON

1. Verify Power is Present.
   Unplug the power box cord and operate a drop-light in the 3-prong receptacle verifying an acceptable voltage and current.


2. Check for Shorted Cells
   A shorted cell can prevent the indicator light from coming on. Remove both cells, with door back in place operate without cells. If the unit now appears OK with indicator light ON, then the cells have a problem.
   
   
   1. Operate without cells
   2. Check cells for broken wires
   3. Check cells for bent plates
   4. Check with one cell at a time (align cell with contacts)


3. Replace or Repair Power Box.
   If the power box is plugged in to 120v and the LED indicator still does not light without the cells (blower must be running), then the problem is in the power box.

• Check the on/off switch, 3-Prong Connectors, and wiring.
• Bypass the Air Flow Sensor (AFS), The AFS is a switch that closes when air flow is present. By-Passing the AFS will force on the power supply, See AFS By-Pass section below.
• An LED problem is not likely if the cells never spark. The LED will not light if its blue and white wires are crossed.

SST Power Box Bench Test

When there is no air flow and the SST is turned on, it is normal operation for the green LED to come on for 10 seconds and then turn off. If this behavior exists with the blower running, then inspect the thermistor orifice for a clog.

The AFS uses a thermistor to sense air flow, see photo. The thermistor heats up to 120 degrees and when cooled with air flow, the circuitry switches the power on. The vacuum in the duct draws air through the orifice and cools the thermistor.

To bench test the power box, we use the setup shown below. Our fan draws a vacuum near the AFS orifice and we move the fan away until the green LED goes out. We compare this sensitivity to our test unit.

The most simple test is to just blow at the orifice with a straw. Use a mirror (shiny galvanized sheet metal) to watch the LED on the other side of the power box. The LED will turn on as soon as you blow, and go off with in a second after stopping. A hair dryer would also work.

A thermister is a device that changes resistance with temperature change.

Beware of electrical shock. The contact and rivets are live at 6200 volts.

• Power Supply Test
• AFS Test Procedure

Air Flow Sensor By-Pass Test

To test the power box without air flow requires by-passing the air flow sensor (AFS). The AFS is a switch that closes when air flow is present. The 120v power passes through the AFS switch and on to the power supply.

The AFS connects or disconnects the neutral side of the 120v. The 120v neutral wire passes through the AFS and then on to the power supply. The neutral wire enters the AFS on the white wire, and exits the AFS on the white/brown wire.

By-passing the AFS applies the 120v power directly to the power supply. This will cause the power supply to operate with or without air flow.

The AFS by-pass can be used to isolate a problem with the power supply or AFS. If the power supply operates with the AFS by-passed, then there is a problem with the AFS and not the power supply. The collector cells need not be connected.

Photo below shows by-passing the AFS. Disconnect the modular plug from the AFS and then connect the white wire to the white with brown stripe wire. We did this using the yellow wire shown below. We used a 14 gauge wire because if fit snug in the connector. This will force on the power supply and the green LED will light.

• AFS Installation
• AFS Test Procedure

Replacement Parts Warranty

The White-Rodgers warranty for all electronic air cleaner replacement parts is one year. Our customers simply ship us the defective part. We test and confirm the part is defective. We then ship back a brand new part at no charge.

• Parts Warranty