AprilAire Evaporative Humidifiers Product Training Webinar (Recorded November 2019) 

I am home owner and engineer. I found the humidistat did not click at any point and the red light was on and no solenoid voltage. This video provided O/S temp sense resistance values. I checked mine and got 3.6K on a 30 degree day. I used a 40K resistor across the terminals and guess what? The red light went out and the dial did a click at "5" and the solenoid activated. This is a long winded way of saying THANK YOU VERY MUCH ... well done. Now to replace sensor.

This is ridiculously helpful. Thank you. It would be nice, however, to see mention of return duct installation. Many homes do not have available vertical supply ductwork which require return duct installation.

i just purchased the aprilaire 700 M to replace the almost identical Bryant 757M which was connected to my HUM board via a Honeywell R8222B 1067 24V 50/60 Hz; it did not use a transformer. May I simply use the current wiring and therefore not use the provided transformer?