Nest - Solenoid on bypass humidifier not engaging - 16v output on *


Old 11-23-14, 07:53 PM
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Nest - Solenoid on bypass humidifier not engaging - 16v output on *

Hi all, hoping someone can help.

I cannot get NEST to activate the solenoid. Heat, Cool, Fan all work fine.

I decided to measure the voltage for '*' from nest to 'C' on furnace terminal and get 16V. What do I need to do? Shouldn't nest be putting out 24V from '*"?
1. * (star) is connected to one end of the solenoid
2. Other end of the solenoid is connected to 'C' terminal at furnace.
3. 'C' is also run from the furnace to 'C' on nest.

1. Bypass Humidifier - 24v solenoid (U147112 - 24/60)
2. Furnace: Lennox G43UF. Terminals W C R G Y - all 24v

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Old 11-23-14, 08:01 PM
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Welcome to the forums.

I have seen some humidifiers draw too much current and drag the * output from the nest too low for the humidifier to work.

What is the input voltage at the nest when the * is at 16vac ?
If you disconnect the humidifier.... does the * voltage return to +/- 24vac ?

You may need to have the nest control a relay and then use the relay to operate the humidifier.
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