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My old Aprilaire 760 died last week so I bought a new Aprilaire 700 manual and installed it but I'm having difficulty with the wiring. The way I hooked it up (see diagram below) includes a relay in the system to sense when the heat is activated and the solenoid is powered by the 24v R terminal. It works and gets heat to temp it needs and humidity to where it needs to be but the fan now runs 24/7. Not sure why this is given that I didnt wire anything to the fan terminal. If it matters, I have a nest E thermostat. How can I properly wire this to turn on when heat is running only and do I need the relay? I'd rather not have the fan permanently stuck on. Can I instead power the solenoid through the W terminal only (diagram attached)? Thanks in advance!
 

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There's nothing wrong with either of your wiring diagrams. Either should work and have no effect on the fan circuit, as you know. That problem lies somewhere else.

Below is a link to a good list of things that can cause the furnace fan to run continuously. Hopefully one of the items listed will be your answer.
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Fan Running Continuously Causes
 

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And yes, you can power the solenoid directly from the W leg of the thermostat but using the relay is preferred by some. Your choice. The solenoid only requires .08 amps (80 milliamps) so it's no big added load.
 
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