Goodman GMH95 Furnace and Honeywell 360A humidifier interference

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Old 11-16-18, 01:43 PM
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Goodman GMH95 Furnace and Honeywell 360A humidifier interference

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Mavericks:


We purchased a home recently, and have run into an issue with the humidifier and furnace. I have a Honeywell 360A humidifier mounted on our Goodman GMH951155DXAD. The humidifier control board seems to have a fried transformer, so I purchased a replacement humidifier of same kind, and tried to do the simple swap of the whole humidifier. The wiring to the furnace and the humidistat is the same as before, and I have confirmed that it is according to the circuit diagram in the furnace manual for humidifier (page , and according to the humidifier circuit diagram (page 12 in Honeywell 360A manual). Oddly, when the humidifier is connect to the furnace, it causes the inducer motor to not fully come on and stay on. This is exactly as described by the this forum thread, except that this happens only when the humidistat calls for the humidifier to be on and if the humidifier is connected to the furnace C (on control board) and COM on the ID pressure switch. On 12-03-15, 06:32 PM you posted that you have a thought, especially if there is a humidifier. I do! Can you please help troubleshoot and fix?

My alternate option is to by-pass the furnace completely and use the pressure switch provided with the replacement humidifier. I just am trying to avoid cutting sheet metal on the ducts to accommodate this.

Steps taken:
1. From the wiring coming from the furnace and humidistat, there is ~24.6 V AC only when the inducer motor is running and humidistat is calling for the humidifier. Else, it is 0 V AC.
2. Humidifier runs when disconnected from the furnace/humidistat, and the yellow wires are shorted (i.e. completing that loop).
3. Voltage across these yellow wires is ~27 V when not connected to anything.
4. Furnace control board LED stays solid even when the inducer motor doesn't fully operate.
5. Furnace cycles the inducer motor about 15 or so times, then shuts off. No LED errors though.
6. Once the cycling of the inducer motor starts with the humidifier in the loop, it doesn't correct itself even if humidifier is power off.
7. I hear three clicks when this cycling happens. First, when the furnace turns on inducer, second when it shuts off the inducer, third a few seconds after the second. Then the click again after a few seconds to try to start the inducer again.
 
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Old 11-16-18, 01:48 PM
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Welcome to the forums.

First off...... that 360A is a self powered device. That means it supplies it's own 24vAC power and cannot be directly connected to the furnace. You'd need to use a relay to isolate the furnace from it.

If you want the furnace to control the humidifier so that it needs to be heating for the unit to work.... a relay gets connected to C and W or HUM at the control board. Then the two switched leads of the relay get connected to the humidifier.

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Old 11-16-18, 02:41 PM
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Thank you for the quick reply!

I understand what you have mentioned here. I will try with the relay as you have suggested. Will update.

A minor thing: It is a Honeywell HE360A1027 (sorry for stating only the 360A), but it is also a unit that is self powered with the 24 V.

Since I didn't change the wiring configuration for the humidifier, I am just surprised that this exact humidifier unit (although from 2010) has been directly connected to the furnace all these years. A month ago I had the furnace cleaned and serviced by the same company that installed the furnace, AC, and humidifier, and they didn't catch this either. Makes me wonder if the humidifier ever worked since 2010!

Thank you!
 
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Old 11-16-18, 03:28 PM
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You're lucky more damage wasn't done. When the 24vAC from the humidifier meets the 24vAc from the furnace..... certain parts can see 48vAC which is hazardous to their health.

I could never understand why Aprilaire and even Honeywell chose to use this method.
 
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