My Aprilaire 700 works in test mode only. It will not work when the furnace is running. Red wire from humidifier control is connected to HUM terminal & the white wire is connected to furnace 24V common. Could this be a bad temperature sensor? Can I get this to run without the outside temp sensor?

Depending on the age of your furnace you may have an aux terminal for a humidifier. If not, you should use the white wire (heat) coming from the homes thermostat to power up the humidistat and ultimately bring on the humidifier. This way it will only run when in heating mode.

If you don't have a volt meter, purchase one. I've seen them as low as $20.00 at Sears and even lower at Home Depot and other discount stores. The HUM terminals are most likely low voltage (24v). The "N" is the neutral. Assuming you have confirmed this is low voltage (24v, you will use HUM and "N" terminals. This control sequence is typically to allow for operation of your humidifier only when there is a call for your fan to run. The brown wires coming from your Humidifier are your low voltage circuit. One should be directly wired to "N". The other should be ran to your humidistat. The other side of the switch of your humidistat should be wired to the HUM terminal.
I hope you will find this helpful. Good Luck!!!!

Okay, I looked up the installation manual online to see exactly what you are working with.
Yes the R anc C need to be hooked to the transformer supplied with the unit. The primary 120v side needs to be hooked into the power coming into the furnace. this can easily be done were the L and N get hooked into your furnace or circuit board on the furnace. This will provide the contiuous power to the unit. Preferably you will hook this after the door switch of the furnace so that you will kill the power toit if you take the blower door off.
The ODT terminals are for the outdoor sensor if you want to hook that up it will vary the humidiy in your home according to the outdoor temperature then.
Now the W/G and Cf terminals. If you have 24v coming from the HUM terminals of your furnace you DO NOT need a second transformer. You must check your furnace manual or check the voltage to them with the furnace blower energized. The HUM terminals will only have power to them when the blower should be running.
If the HUM terminals are 120v then you need to get another transformer and hook up the primary side to the HUM terminals so it is powered only when the the blower is running. Hook the secondary side to the W/G and Cf terminals.
So bottom line is that you need to figure out what voltage your furnace is giving to the HUM terminals and then go from there. Some times the EAC terminals or the ACC terminals will be 24v on the furnace board. Either of them could be used also, as they are only energized when the blower is running also.

Heatman101

That will work, The HUM feeds power to the humidifier when the fan is operating even in cooling on most models, However the humidistat must also be calling for humidity and probally won't call during the cooling months

You have a faulty humidistat

Greg Sunsetmech

connect two wires at humidifier without any wirng connected if works problem is in wiring or humidistat

i believe e3 is an outdoor sensor problem, most people use manual mode, you should see a blue jumper that is connected to 2 OD terminals at the control, or if u use a sensor there should be a wire run outdoors, if you dont have the manual mode part you have to get it from an aprilaire dealer, cant just jump it out, it is a resistor

I just solved a problem with mine today.  One of my low voltage power wires to the humidity control had a bad connection.  I reconnected it and I could again hear the solenoid valve clicking as I adjusted the dial control.
I found the problem with a voltmeter:  there was voltage at the power terminals on the humidity control terminal board, but there was no voltage at the solenoid valve terminals.  It was hard to push my big wires into the terminal board, but I finally secured the connection!

You want the humidifier to run in heat mode which is the r-w1 terminal on the stat.

if humidifier was wired into thermostat circuit for power instead of seperate transformer , this can happen. you need to see if you voltage going to the solenoid valve. if you do , and it isn't opening, the valve is bad . this is assuming that it is using a # 50 relay to come on only when the fan runs . . make sure the water valve is open