Connecting Aprilaire 600M to new thermostat


Old 10-10-14, 07:18 AM
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Question Connecting Aprilaire 600M to new thermostat

I currently have a Aprilaire 600M hooked up to my Carrier 59TN6A. One red wire coming from the manual humidistat going to the yellow wire of the 600M solenoid. The other yellow wire of the solenoid is connected to the other end of the red wire from the humidistat then that wire is plugged into my HUM terminal on my furnace (24V). The white wire coming from the humidistat goes to the C terminal in my furnace. I'm looking at getting the Honeywell TH8321U1097 thermostat. This will control the humidity as well. I'm looking for the humidifier to only run when heat is on. I'm looking for wiring assistance. I have 2 spare wires running to my current thermostat. I've read other posts that state I need to run one of the yellow solenoid wires to the C terminal on the furnace, but that isn't how it's hooked up currently. Is this correct?
I'm thinking that I could use the spare orange wire. Hook one end up to the U1 terminal on my Honeywell thermostat. Splice in one of the yellow solenoid wires into that, and plug the other end into the HUM terminal on the furnace. Hook the other wires up on the thermostat as normal. Connect the other yellow wire from the 600M solenoid to the C terminal on the furnace. Unhook the manual Aprilaire humidistat completely. Does this sound correct?
Any help would be appreciated.

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Old 10-10-14, 08:30 AM
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Welcome to the forums.

The t'stat comes preprogrammed to humidify only when blower is on.

I believe you can run that t'stat off batteries and not use a C connection. But you have two spare wires so why not connect it. You'll need one wire for the humidifier and one wire for the C connection.

You would need to connect one of the spare wires to one of the U1 terminals. You would need a short jumper to connect the other U1 terminal to the red Rc/Rh wire.

At the furnace end.... the wire from the U1 terminal goes directly to the humidifier. The other wire from the humidifier goes to the C terminal.

Link to the install manual.... TH8321U1097Install.pdf
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