TrueSTEAM not turning on A.H. fan


Old 11-07-10, 05:04 AM
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Join Date: Nov 2010
Location: USA
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TrueSTEAM not turning on A.H. fan

Please help me figure out what's wrong...

I've added a Honeywell TrueSTEAM humidifier (model HM512) to my 4-ton Amana heat pump (air handler model AEPF4260) which used to be controlled by a Honeywell VisionPRO TH8320U thermostat, but which I replaced with a VisionPRO IAQ. I included an outside temperature sensor from the tstat relay board.

I have wired and configured it for "OPTION 3: VisionPRO IAQ Wiring with Fan Delay", which effectively inserts the humidifer BETWEEN the tstat and air handler with regard to the G (Green) fan wire. The tstat is able to turn on the air handler fan when it calls for heat, which means that the pass-through of the G fan signal through the humidifer is working, the humidifier itself fails to ever turn on the fan by itself when there's a call for for humidity without heat. I've waited for over a half hour, and have heard 15 minutes worth of boiling, so the 176 degF fan turn-on threshold for the humidifier should have been long reached.

I should have all the wiring and configuration correct, although there simply must be some problem on my end (rather than equipment mis-design).


- Three wires from tstat display to tstat relay board. These communicate properly because both heat and cool work, as well as call or not-call for humidity.

- C,R,Y,Y2,O/B,AUX wired direct from tstat relay board to air handler. I haven't specifically checked for second stage cool or heat, but at least first stage of each work. Any second stage problem shouldn't relate to my fan situation anyway.

- Two HUM wires connect tstat relay board to humidifier

- R,C wired from tstat relay board to humidifier, and humidifier dip switch 4 is down such that TrueSTEAM looks for R input before allowing humidity. Note that wiring recommendation omits C, and before I connected C I got the expected 7 blinks on the red service light, meaning "HVAC Power Not Present". This subsequently made sense, because it can't see power on R without having a common reference on C. So in spite of this connection missing from the manual, I added it and the humidifier steaming action began working. This specifically proves a good electrical connection of both C and R to the humidifier.

- G (fan call) from tstat goes directly to humidifier GT terminal, and then from humidifier GF terminal it continues to the air handler. The electrical connections are certainly good here, because when the tstat calls for fan, the air handler fan comes on. This specifically proves a good electrical connection from the humidifier to the air handler fan.

NOTE at this point that I've proven good connections of C, R, and G with the humidifier. My *BELIEF* is that in the delayed fan mode, when the humidifier sees 176 degree water, it closes a relay between R and GF which should turn on the air handler fan. (It might also open a normally closed pass-through relay between GT and GF, so as not to back-push the tstat. But this question is not germane to the issue.)


- On the humidifier all six dip switches are down. The germane settings are dip4 (look for R input before allowing humidity) and dip5 (do NOT look for air movement through an air proving device, which I don't have).

- On tstat #0374 = 3, "Humidifier operates independent of fan", which is the setting specified by the humidifer manual when one wants fan delay. I *BELIEVE* this simply means the tstat will NOT call for fan as a result of calling for humidity. Instead, the humidifier later takes it upon itself to call for fan (as discussed above for wiring).

- on tstat #0372 = 1, "Humidify (no frost protection)". This isn't germane to the issue, but introduces another question. I don't know what frost protection would be, so I doubt I have it. On the other hand, the COMPLETE indoor systems are all inside conditioned space (sealed attic with spray foam under roof). So, the only thing that could possibly frost is the outdoor unit. I believe I should change this setting to #0372 = 3, "Humidify (with frost protection)", but I'm unsure. For safety sake, I set it for no frost protection. Please advise if I can change it to frost protection. I assume the no frost protection setting may lead to the humidifier being needlessly turned off when the outside temperature sensor is below freezing.

- on tstat #0370 = 1, "Internal sensor in thermostat", referring to humidity sensor.

Thanks very much.
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Old 11-07-10, 05:53 AM
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Join Date: Nov 2010
Location: USA
Posts: 11

I subsequently discovered a missing jumper on the humidifier from R to RT. I added this. Now the humidifier successfully puts 24VAC on GF to the air handler, even when there's no 24VAC on GT from the tstat (it reads 15VAC residual) . So, evidently, the humidifier connects GF to RT, not R, when it wants fan. This is INCONSISTENT with the manual. Replacing this jumper should, however, fix my initial problem with the humidifier calling for fan after a water heat-up delay.

However, I also found a different problem. The variable speed fan of the air handler is coming on at a very slow speed, and after 20 minutes remaining at such slow speed. I confirmed this using the tstat fan-on setting, while having humidity control turned off and heat effectively disabled by a low temp setting. Safely assuming the same behavior when the humidifier does the fan-only call rather than the tstat, MY CONCERN is that the air flow CFM will not be sufficient for the TrueSTEAM's minimum requirement. I believe I need the air handler's variable speed fan to run faster during a fan-only call (air handler G=24VAC and no others energized).

Is there a way to make this happen? The situation must reside completely in the air handler itself, since there are no other wires going to it to control actual fan speed. There's just the smarts in the air handler for how fast to run the fan, typically based on number of stages of heat (or cool) called for and I believe also the amount of time passed.

Thanks for your help.

Last edited by Dr.Lightning; 11-07-10 at 07:52 AM.
Old 11-07-10, 08:57 AM
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Join Date: Nov 2010
Location: USA
Posts: 11
Now I find info in the manual. While I have an Amana AEPF4260, the doc is thin. There's more doc on the Goodman AEPF4260, which seems to be the same equipment.

The manual says fan-only mode is at 30% of cooling setting. Cooling setting should be 1580 CFM. I haven't confirmed dip switch settings for that. This means 474 CFM in fan-only mode. However, I had no choice but to install mid-way on the largest of three supply ducts, sized 12", 10", and 8". I calculate roughly 50% air flow through the 12" duct, and this gives me 237 CFM in fan-only mode.

This is a hair below the TrueSTEAM's spec of 250 CFM, which is not only in the manual but also confirmed in the past by Honeywell tech support. 237/250 is 95%, which ought to be close enough.

Alternatively, I believe I can switch some dip switches to get 10% more air flow. This will bump me up to an estimated 261 CFM, which is 104% of the TrueSTEAM minimum.

HERE COMES MY QUESTION... I also see in the Goodman doc that if one connects a humidistat and cuts jumper JP6, then "The Humidistat will only affect cooling airflow by adjusting the Airflow to 85%." The grammar is a little ambiguous here, but I believe it means that when the humidistat is "calling", the fan-only airflow will be 85% rather than 30%. This would bump me up to a healthy 672 CFM in my selected duct, without even the dip switch selectable flow increase of 10%.

Is my 85% vs 30% understanding correct?

To do this, the Goodman doc mentions a humidistat relay between the air handler's R and HUM terminals. This humidistat opens on humidity rise. I think that means it closes when the humidity is too low and more is desired. This translates into the statement that the "HUM" input gets 24VAC on a call for humidity. I further understand this to mean that, if I cut jumper PJ6, then a call for humidity on air handler's "HUM" terminal will get me 85% fan CFM. It *probably* even does so WITHOUT seeing a call for fan on the "G" terminal.

So I'm thinking about devising my own wiring update. I still need G getting from the thermostat to the air handler. Right now this goes through the humidifier. I'd cut out the humidifier and run G directly from the tstat to the A.H. Next, I'd take the GF output from the humidifier and run a new wire to the A.H. "HUM" terminal.

I believe the behavior would be the following. When the tstat wants fan due to cooling or heating, it will do it's regular old thing and the A.H. will act as one would expect. Also, if the tstat is switched to fan-only, the A.H. will produce 30% CFM. This is all as if the humidifier didn't exist.

On the other hand, if the tstat calls for humidification, the humidifier will start heating water. Only after the humidifier sees 176 degF will it energize the GF terminal. This GF terminal, wired to the A.H. "HUM" terminal, will cause the air handler to run at 85% CFM. Voila! More than enough airflow for the TrueSTEAM.

Does this sound correct?

I even think there are spare wires in my cables between humidifier and tstat relay board, and between tstat relay board and air handler. So I can daisy-chain this GF-to-HUM connection through existing cables, using a wire nut inside the tstat relay board box to connect the newly purposed humidifier GF wire to the newly purposed air handler HUM wire.
Old 11-07-10, 10:06 AM
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Join Date: Nov 2010
Location: USA
Posts: 11
The air handler HUM terminal doesn't do what I thought. At this point, I figure it must refer to DEhumidification and not HUMidification. Correspondingly, cutting PJ6 and energizing the HUM terminal must cause the fan to REDUCE cfm from 100% to 85%, so the coil will get much colder ("super cool?") in order to draw more moisture out of the air and DEhumidify.

Fortunately for me, the dip switches were already set for +10% air flow, and I should be marginally above the TrueSTEAM minimum of 250 CFM.

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