Aprilaire 600 to Trane GSUF


Old 11-16-14, 03:13 PM
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Aprilaire 600 to Trane GSUF

I had an Aprilaire 600 installed many years ago with my Trane GSUF. Problem has always been the humidifier runs whether the blower is operating or not. Thermostat seems to work fine, but it always leads to the humidifier running water during times the blower or fan is not running. Waste of much water. I could run the fan on low speed all the time (have done that at times), but I'd prefer the humidifier runs water only when the blower is running.

Currently (no pun intended), red wire runs from humidifier thermostat to R on terminal board inside the GSUF and white wire runs to B. Left to right, terminal board is:
T R Bk O Y Ylo G W1 W2 W3 B

Everything else on the humidifier seems to work fine.

This is a 1999 era Trane GSUF and a 2003 Aprilaire GSUF. I'm not terribly confident using a voltmeter on the board to find a blower switched terminal, so any help would be appreciated.
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Old 11-16-14, 07:29 PM
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You've got a pretty complicated system there with the ground source system.

Right now you've got the humidifier connected to R=24v and B=common. That means if the humidistat calls for humidity that unit will run at any time regardless of blower status.

There isn't a user accessible blower switched output that I can locate on your GSUF unit.

The easiest way around the problem is to install a sail switch in the air stream. When the blower runs... the humidifier can run. In the summer you'd turn the humidistat to off.
Old 11-16-14, 07:53 PM
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Thanks for the info. Yes, correct. If the humidistat calls for humidity...it runs. Perhaps the setup you interpret is why it was installed the way it is. I do recall mention of "keep the low speed fan on all winter." I've been kind of 'manually' running the humidifier all these years, as it takes a pretty big temp swing to affect it and I hate hearing water running 24/7. As we are already feeling the effects of dry air this year, we probably want it running more than less. At the cost of a higher water bill, I will probably just pay it and try to keep the humidifier doing its thing as much as possible. During the coldest days, it does run less (humidistat) and the geothermal system keeps the blower running 50-55 minutes an hour. I guess I will live with it. Thanks again.
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