Humidifiers and Dehumidifiers - aprilaire 600 and Rheem Classic 90 + mod

Hello, I just changed the filter in my Aprilaire 600 humidifier and with the furnace running turned the dial to test. the humidifier didn't come on. The humidifier is about 6 years old and was installed on a Rheem Classic 90 plus modulating furnace 2 years ago. I checked the wiring and found that the humidifier was wired through a transformer to the EAC terminals and not the HUM terminals. Now, acording to the Rheem installation instructions the EAC terminals are powered only when air flow is above 800 cfm. This might explain why the humidifier didn't work when I tested it. But I'm wondering if there is a better way to wire it. What I can't figure out is how to use the HUM terminals. the manual says they are "dry" contacts on the IFC connected to a board mounted relay. The coil of the relay is controlled by the IFC....the humidification is active anytime the heat blower is active. I tested the HUM contacts with a multimeter with the furnace running and got nothing. Does dry mean not powered? If so where do I get 24 vac? Thanks

I am going to have to look it up for your furnace.

What is the model # of the furnace itself?

The model # is RGFD-12ERCMS. Thanks for your help.

the HUM on the board is just a switch (no power).

So, you can remove the transformer, and set one of the humidifier wire on to one of the humidifier screws. then from the other humidifier screw, run a jumper wire from that to R (where t-stat hooks up)


Then the last wire from the humidifier over to C (where t-stat wire hooks up)


See Fig 58 of the install manual.

Thank you! That makes a lot more sense than using the EAC terminals.