Better spot for 24V transformer?

Nothing like choosing a weekend with forecast temps below 0 to be futzing with your furnace!

Looking at the wiring for my Aprilaire 500, I need to pick up 24V DC for the solenoid. From my reading on this forum, one option is to pull the power from either the HUM or EAC connections on the Trane XV80 circuit board and to mount the transformer in the upper cabinet (based on Jay's photo).

Near my furnace is a junction box where I could also install the 24V transformer (there is already one there, for the doorbell, I think). I could mount on the other side of this junction box. The furnace control area and the wall junction box are roughly the same distance from the planned locations for the humidifier/solenoid and the humidistat.

Any preference as to the wall junction box or using the furnace for the transformer?

The first drawings shows the following:

Yellow: Planned Humidistat location
Red: Planned Humidifier location
Green: Junction box on wall where I could install transformer
Blue: Furnace area where I could install transformer

If I use the furnace, I -think- I tap into the HUM or EAC on the top of the circuit board, as highlighted in RED in the second drawing. From what I understand, the HUM connection would limit power to when the HEAT is called for, the EAC connection would provide power whenever the FAN is going. Of course, if I wired to the wall, 24V would be supplied all the time, which could be an issue if the solenoid failed, or the control circuitry failed. Maybe I just answered my question...


Thanks for any advice!

John

 

Looking again now, it looks like both the EAC and HUM connection from the right, top of the circuit board are already connected to wires that route to the upper chamber, and look to go into the metal box on the left.

Thoughts?

Thanks,

John

 

The primary leads of the 24V AC transformer should go to HUM and Neutral on the control board. The transformer can be mounted on a box attached to the side of the furnace.

 

Thanks Kevin. As I mentioned, the HUM (and EAC) are both already connected somewhere up on the upper cabinet. I'll have to see where those wires go. Would it be OK to double up off of those connections?

 

The HUM may be going up to the junction box in the upper cabinet.

You'll have to wire the Neutral side on the line coming into the box, I'd suggest going only on HUM for the hook up.

This is how I have mine wired.

 

Yes, the wire went up towards the junction box. I'll have to power it down and open it up tomorrow and take a look to confirm.

Thanks for the input, Jay.

 

Stay warm this weekend!

Do you have a two stage stat wired to this furnace?

 

It turns out that I'm not taking advantage of my two-stage thermostat! I figured this out in the last couple of days, reading the thermostat forum here. My thermostat can handle two stages, but when the new XV80 and A/C was installed about 8 years ago, the contractor didn't bother to suggest we upgrade the wiring. I was looking at it last night. It will be a bit of work to fish the wires, but it should be doable. The basement below the thermostat is unfinished.

FYI - I have the outside temperature probe installed and wired to the basement. I also installed the humidifier unit on my return today after work. That sheet metal cutting was a pain! I'll try to finish it all tomorrow.

Stay warm yourself over the next couple of days!

John

 

Take it you don't have enough wire behind the wall to hook up the 2nd stage?

Let us know if you need any thing else!

We are tough Minnesotian, so i am ready for a deep freeze! :-)

 

We are a hardy lot! I'm OK with the cold, as long as I don't screw up my furnace with the humidifier project I need two more wires between the furnace and the thermostat. My background is data networking, so running cables is not foreign to me.

John

 

With that back ground, doing this project shouldn't be an issue for you! ;-)

Just make sure you turn off the power to the furnace.

 

FYI, there are thermostats available that communicate to an Equipment Interface Module that uses only 2 or 3 wires. The EIM then mounts near your furnace and controls all your HVAC equipment including your humidifier. This also moves all the relays (normally in your thermostat) near the furnace and not in your living space where you can hear the relays click when the heat turns on and such.

 

Another nice thing about this t-stat that Kevin was talking about, is you can control the humidity in the summer by slowing down the blower speed.

 

Interesting T-stat. I'll keep it in mind if running the wires turns out to be too much hassle.

I ended up wiring my 24V transformer as you showed. That all went smoothly.

 

Glad to hear it went smooth!

Just dont' get blown away tonight!