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Discussion Starter #1 (Edited)
I installed an AprilAire 700A whole-house humidifier a couple of years back and had it was working great using the included humidistat. Over the summer I had my furnace replaced with a Trane XV95 and a Trane XL950 (ComfortLink II) thermostat installed. Since the XL950 is also a humidistat I removed the AprilAire humidistat and everything is supposed to be wired so that the 700 is directly controlled by the XL950. Unfortunately, the humidifier isn't kicking on at all and I'm curious if the furnace installers hooked everything up correctly or if the humidifier simply bit the dust.

So two questions:
1) is the 120-24 transformer that was required with the AprilAire humidistat (connected to the R and C terminals) still required when using the XL950 as the control unit? If so, what do I connect the transformer too?

2) How should things be wired so that the XL950 can control the 700?

I've verified power to the blower fan on the 700, that the two (brown) wires coming off the 700 are connected to the HUM terminals on the XL950 relay panel, water pressure at the humidifier where it enters the solenoid and that the XL950 is configured to use a humidifier.

Thanks,
Corey
 

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Discussion Starter #2
Had the furnace guy out today to look at the situation and wanted to post the results in case it helps someone else.

When pairing the Trane XL950 (ComfortLink II) thermostat with an AprilAire 700 whole-house humidifier, the 120-24 transformer IS required. Here's how we connected it:

Wires from the 120v HUM terminals on the furnance circuit board connect to the 120v side of the 120-24 transformer. Connect one of the wires on the 24v side of the 120-24 transformer to one of the brown wires coming off the humidifier and wirenut together. Connect the other wire off the 120-24 transformer and the other brown wire coming off the humidifier to the HUM terminals on the XL950 Relay Panel to complete the circuit. Verify the thermostat is configured to use a humidifier and you're all set.
 
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