Why two 24 Vac on aprilaire 700's control unit?
Aprilaire 700's control unit has terminals marked R, C, A, B, ODT, W/G, Cf, and H. The schematics indicate that A, C are connected to a 24Vac transformer that is continuously on, and W/G, Cf terminals are connected to HUM via a 24 Vac transformer. Why does the control unit need two inputs, or does it mean that continuously powered transformer (to R, C) is not needed if W/G, Cf are connected to HUM terminals via a 24 Vac transformer? What do W/G and Cf terminals stand for?
Humidifiers - Aprilaire - 700 Humidifier
Answers & Comments
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