Aprilaire 24V Sensing Relay, 50

After my furnace-mounted humidifier stopped working, I did a little troubleshooting and determined that my orginal "#50" relay was the culprit. I've fixed a couple problems with my furnace over the years and this is most definitely a DIY fix so long as you are able to determine that it is in fact a bad relay.

What this relay does is ensures that the humidifier only runs when the furnace blower is running. If replacing an old one, simply wire it the same way the original one was wired. If it is a new humidifier installation, follow the instructions included with the humidifier and/or this relay.

I got this to go along with my Honeywell (360A?) whole house humifier. The first one they sent me did not work. But, with only an email request, they shipped another one quickly with an apology for my inconvenience. I'd do business with this company again.

If you get the Honeywell humidifier, you really want this relay or you'll waste a lot of water keeping the element wet while the furnace fan isn't running.

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Product arrived quickly and worked great. I have a Honeywell bypass style whole home humidifier that used a sail switch to make sure you weren't wasting water if the fan was off. The sail switch always had problems and never really worked well. This product will save me water and should be reliable since there are no moving parts to break.

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The relay is now installed and has worked well. Resonably priced and quick delivery seals the deal. Thank you for having this product available.

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I added a humidifier to my forced air furnace in order to bring up the humidity in our house to reduce the shrinkage on our new hardwood floors. Cracks between the boards were starting to appear due to the low humidity during the winter. Researching reviews of various humidifiers, I found many complaints about motor failures on drum type humidifiers and also complaining that the humidity never got as high as they wanted. The wiring diagram supplied with most of the humidifiers does not include an AC current sensing relay such as this one. They connect the drum motor in series with the humidistat, directly to 24vac from the furnace or from a separate 24 volt transformer. With this connection, if the humidity never gets high enough to satisfy the humidistat, the drum motor will run 24/7/365 (continuously) and probably fail prematurely. I added this AC current sensing relay in series with the humidistat and sense the AC current going to the furnace fan motor. With this configuration, the drum motor only runs when the furnace fan is running and the humidity is below the set point of the humidistat. Works great and I have increased the inside humidity about 15%.

One note: I tried to test the current sensing relay before installing it. I used a volt-ohm meter to verify that the circuit was closing when the AC blower motor was running. The volt-ohm meter never detected a switch closure like I expected (dry contacts of a reed relay?). I went ahead and wired it into the 24vac circuit and it worked fine. So, the device is not a set of dry contacts as I had assumed, rather an active circuit that needs the 24vac to operate. I resisted the urge to tear it apart and see what was inside.

As a side note regarding the humidifier: I chose the drum type humidifier since it consumes less water than a flow through type. Water usage is a concern out here in the dry western states.

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