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Aprilaire 4740 Humidifier Fan Relay for 700A 700M


Aprilaire 4740 Humidifier Fan Relay for 700A 700M
Retail: $22.99 /ea
You Save: 26%
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Retail: $22.99
You Save: 26%

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Product Information

The Aprilaire 4740 is the correct replacement for the following humidifiers:

  • Aprilaire Model 700A Humidifier
  • Aprilaire Model 700M Humidifier

The Aprilaire 4740 Humidifier Fan Relay is a replacement relay that powers up the circulator fan in the latest Aprilaire 700 model, 700A and 700M humidifiers since 2008. Newer versions of the 700 model series uses an external transformer to power the control circuit, along with the Aprilaire Fan Relay. Older versions used part number 4238 that contained a small circuit board with a low voltage transformer. 120 volts could cause serious injury from an electrical shock, so be sure to unplug the power to your humidifier before servicing.

The tools you will need for installing your fan relay are a Phillips screwdriver and a pair of needle-nose pliers. Installation instructions:

  1. Remove cover and place on a flat work surface with the fan blade facing up.
  2. Push receptacle out from orifice place by pressing tabs in.
  3. Use Phillips screwdriver to remove the 4 screws holding the orifice plate and bridge assembly into cover.
  4. Lift orifice plate out from the bridge assembly and lift the bridge assembly out from the cover. Place bridge assembly on a flat surface with fan blade facing down.
  5. Use needle-nose pliers to disconnect the power cord, fan and humidistat/solenoid valve terminals from the old relay.
  6. Use Phillips screwdriver to remove 2 screws that fasten the relay to the bridge assembly.
  7. Discard old relay.
  8. Place the new relay onto the bridge assembly and re-attach using the 2 screws you removed.
  9. Connect the black and white power cord terminals and blue fan terminals to the replacement relay.
  10. Connect humidistat/solenoid valve wiring terminals to replace relays.
  11. With fan blade facing up, place the bridge assembly back into the cover. Make sure that the power cord is lined up with the slot in the cover. The yellow and brown wires should be inside the notch and not pinched between the bridge assembly and cover.
  12. Re-attach orifice plate to bridge assembly. Use the 4 screws that you previously removed in step 3.
  13. Attach receptacle to the bridge assembly. Snap receptacle into place.
  14. Replace cover to your humidifier base.
  15. Plug in your power cord and check the operation of the humidifier.


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