Question about Aprilaire 600 Humidifier

3 Answers

Aprilaire 600 only operates in test mode...

The system is installed in automatic mode and operates in "test mode" but will not operate out of "test mode".

Outside temperature is 35-40 degrees and the resistance of the temp. sensor at the humidistadt measures ~27 k Ohm (corresponds to the suggested impedance for this temp.). The humidifier is installed in the supply plenum and the humidistadt is located about 5 feet (farther form furnace) away from the humidifier.

On a side note, I used the manual mode resistor with similar results.

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  • Dragon man Dec 07, 2007

    Have you got your problem fixed? I am having the same problem, only work at test mode and show E3 code once have it set. if you have the problem fixed, please email me thank you in advance.

  • Anonymous Dec 12, 2007

    I have the same problem. My humidifier works in test mode, but won't work in any other mode.

  • chasjl Dec 29, 2007

    Just completed install. My shows 27K ohms from the temp sensor and 30% HH but will not run the humidifier. Test mode works. I think I'll convert it to manual until I can call Aprilaire on Monday.

  • chasjl Dec 29, 2007

    Well, it dosen't work in manual mode either. Only works in test.

  • 34Scarab Dec 30, 2007

    Same Issue, I have a 600A. I have a continue 24v to R & C,
    and 24v to W/G & Cf when heat is called for from the furnace.
    I have 28.5k ohms of resistance in my outdoor temp sensor (35F).

    If the furnace is on and I go to test mode the
    solenoid turns on and the water is applied to the humidifer. If I
    wait 10-15 sec and return the dial out of test mode to a setting of
    7, the humidifer remains on until the call for heat turns
    off. Turning off part seem to be OK. If I repeat the
    process but this time turn the dial CCW, the humidifer will shutdown
    when the dial get around 4, RH of the return is indicating humidity
    level of 40%. I switched to the manual resistor and the same
    results of than the turn off level is at 6 on the dial instead of 4.

    Summary Humidifer seem to know the correct level RH, and it shuts
    down prooerly when the call for heat has end. But it doesn't know
    when to turn on without going in to manual mode. I guess I'll be
    calling Monday also, unless someone has the magic answer. Thanks

  • snuffysmith Dec 31, 2007

    Same as others. Works fine in test mode, shuts off as soon as it is out of test mode. I now find the outside temperature sensor isn't even outside---I traced the wire and found and found the sensor just sitting up above the vent work hanging free as a bird. Is it possible my inside humidity is high enough that the unit just won't kick on? ---Dick G

  • jeffj Jan 05, 2008

    UPDATE: Aprilaire said the humidistats need recalibration so I sent them back to them a couple of weeks ago. Will let you know how it turns out.

  • Raydean Jan 09, 2008

    Same as Jeff. I get a 30% reading only on the humidistat, regardless where the control is set. The test mode does operate the water solenoid.
    I found that the humidifier control circuit board had heated to a point where these were scorch marks on the board above the wire tearmials from the furnace control board. What the this. 600A

  • Anonymous Dec 07, 2008

    Same problem. The read out indicates 47% and has not changed. The unit never turns on except in the test mode. My furnace guy said that it is working properly because it works in the test mode. I will now ask him to replace it.

  • Anonymous Dec 28, 2008

    My aprilare oly operates in test mode and I just replace the filter. How do I get it to work in normal mode



3 Answers

Thank you, got my problem fixed, after spend $275.00 call the service man to come. it come up to all about wrong wiring.all working and happy:) now.

Posted on Jan 05, 2008

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Well I fixed my problem. It was my fault. I was using installation instructions that I printed from the web, they were for a model 600. The model 600A has a different control and wiring. The model 600 required only one 24V power supply to the R & C terminals. I ran the furnace accesssory power (110v) to the supplied transformer and then to the R & C as required by the model 600. But on the 600A this must be run to the W/G & Cf pair and a seperate continuously powered 24V must be connected to the R&C pair. I bought another transformer, wired everything using the correct diagram and it works great. BTW the E3 code indicates an open circuit on the temperature sensor. Maybe you clipped the wire while stapling it to the joists. Good luck.

Posted on Dec 29, 2007


Call Aprilaire and tell them, this is happining everywhere

Posted on Dec 12, 2007

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1 Answer

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Sorry to read about your problem, I hope this helps you out.
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Aprilaire 600 Humidifier


I had this problem several years ago. In order for the water to flow, the outside temperature sending unit must indicate to the controller that it is less than 60F. If not, the unit will not operate outside of test mode. Check the temp outside where your sending unit is (could the sun be heating that side of the house?) and ensure that the circuit to the sending unit is working. I had a bad wire splice inside a wire nut stopping the circuit. Took me a long while to figure it out.

If the outside temp and your sending unit circuit is ok, I wish you luck on your troubleshooting.


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1 Answer

No water at all

does the solenoid click when in test mode, if not check power to panel/solenoid.

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Jan 19, 2008 | Aprilaire 600 Humidifier

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