Solenoid can work when it wants to - what's up?

Discussion in 'HVAC Heating & Cooling' started by jgurland, Jan 18, 2012.

  1. jgurland

    jgurland New Member

    Messages:
    6
    Location:
    Maryland
    Hi everyone-

    I have a furnace mounted humidifier question. My unit doesn't have a name or model number on it, so I'm not sure who made it. There's a company name inside, probably of the seller and/or installer, but I can't find them. (See pictures attached - one is the inside of the unit and the other is the inside of the cover.) But it has a spray nozzle that goes inside the duct and a humidistat that attaches to the return. I noticed some water dripping from the furnace and discovered that there is water spraying from the nozzle even when the furnace is off.

    My assumption would be a solenoid that's stuck in the open position, but I'm confused by a couple of controls inside the humidifier. There are two knobs - one is labeled "Fan Off" and ranges from 80 to 120 (degrees I guess?) The other says "Diff" and ranges from 0 to 50. If I turn the "Fan Off" knob up to a higher number, the hissing of the spray stops. That tells me that the solenoid is capable of shutting off when it's told to and maybe my problem is with a setting on those knobs.

    So my questions:

    1. Am I looking at this incorrectly and I really do have a bad solenoid?
    2. If not, what do those control knobs do and how do I adjust them so I'm not spraying when the furnace is off?

    Thank you for any help and guidance.

    IMG00301-20120118-1634.jpg IMG00302-20120118-1635.jpg
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,820
    Location:
    New England
    If I had to guess, and this is just a guess, I'd say that those controls are for the fan assembly only. The first knob adjusts the temperature of the heat exchanger when the fan is supposed to turn off. The second one determines when it turns on. Let's say you have the first one set to 110 and the second one to 30. The furnace would wait until the heat exchanger's air temp got to 140 (110+30) to turn on, then after the furnace turns off, wait until it dropped to 110 before it turned off (the differential). Having those adjustable lets you help prevent the fan from turning on when it would feel cold coming out of the registers.

    Now, where the humidifier is wiring into this mess, I can't tell you, but normally, you only want the water running while the fan is on, but it appears, yours is able to turn on when the fan is enabled, but not actually on.
  3. DonL

    DonL Jack of all trades

    Messages:
    3,812
    Location:
    Houston, TX
    hj corrected me in his post down below.

    He is correct. He be the Man...




    + Side is that it Sounds like your solenoid is good.
    Last edited: Jan 19, 2012
  4. jgurland

    jgurland New Member

    Messages:
    6
    Location:
    Maryland
    Thanks for the replies, guys. So it sounds like the following is true:

    A. The solenoid is probably good.
    B. The controls are designed for controlling the fan assembly but are probably controlling the humidifier.
    C. It's only going to work correctly if the fan and differential knobs are synchronized with whatever really is controlling the fan and furnace.

    Does that sound right? And, if so, maybe I should find a way to eliminate those control knobs in the humidifier and wire it so it just opens the solenoid when the blower turns on. Do you agree?

    Thanks again, gentlemen!
  5. DonL

    DonL Jack of all trades

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    If You do not have AC, then you could maybe do that.

    Does your thermostat Have a Fan ON switch ? If so does it work ?

    Do you have a Humidistat ? What is the Model or your Thermostat / Humidistat ?
    Last edited: Jan 19, 2012
  6. jgurland

    jgurland New Member

    Messages:
    6
    Location:
    Maryland
    Don-

    I do have A/C. I have two thermostats (it's a zone-maker system) and they both have "fan on" switches. I assume you're talking about the control that has the options for fan on, off, and auto. And yes, the switches work.

    The humidistat is a Honeywell. It doesn't have a model number on it, but it looks like Ones on Google images that are called H49b1017.

    Should I just try to synchronize the humidifier controls with the furnace controls?
  7. DonL

    DonL Jack of all trades

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    Location:
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    There is no synchronize so to speak of. The sequencing does need to be correct.

    Normally The Humidifier should not be running if the unit is not calling for heat, and the blower is not running.

    It sounds like a wiring problem between the furnaces controller and humidistat / Thermostats.

    Or your Sail switch could be stuck ON.
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
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    Location:
    Cave Creek, Arizona
    That is an aftermarket humidifier so its controls would have nothing to do with the furnace's fan operation. More likely the temperature one is to control when the humidifier turned on, so it did not operate at cold temperatures, and the other is the degree/percent of humidification. all of this is specified in item #1 of the instructions. We do not have enough information to know how it is wired, but the solenoid is NOT controlled by ghosts, so something is turning it on and off.
  9. DonL

    DonL Jack of all trades

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    Good Point hj. Very nice observation.

    That H49b1017 Humidstat should have a Sail switch, And that could be the problem, If it runs when the blower is off.
  10. jgurland

    jgurland New Member

    Messages:
    6
    Location:
    Maryland
    HJ - thank you. Obviously I know very little about this topic, so please bear with me. (By the way, all ghosts were removed from the house when I bought it, so they're definitely not controlling the solenoid any longer.)

    It sounds like the humidifier may be wired incorrectly. Let me see if I understand how this system works:

    In layman's terms (that's me) this temperature control knob acts like a switch. When the air temperature is too low, the switch is off so we're not sending water into the cold air. When the temperature is high enough, the "switch" turns on and the solenoid should open.

    So the voltage supplied to that "switch" comes from where? I imagine it should come from the power supply to the blower - so when the blower turns on, the wire to this temperature control knob gets energized and the "switch" can do its job. Do I have that right?

    Let's assume I got that right - then how does the humidifier know when to turn itself off? Must be when the voltage to the "switch" disappears - in other words, when the blower turns off.

    If all of this is correct, then it sounds like this thing is wired incorrectly because when the blower turns off, this control knob is still powered up.

    Please set me straight.
  11. DonL

    DonL Jack of all trades

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    Location:
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    The Voltage is probably supplied from the Furnaces 24 Volt transformer, Unless your Humidifier has its own transformer.

    The Humidstat is what tells when the humidity is high enough and shuts the water flow off or turns it on if, The humidity is low, the temperature is warm and the air is moving.

    The Humidstat also should have a sail switch mounted in the air flow of the vent to detect the air flow.

    I would check that sail switch, before rewiring it.

    Yes you are correct they are just switches.
    Last edited: Jan 19, 2012
  12. jgurland

    jgurland New Member

    Messages:
    6
    Location:
    Maryland
    Don, looks like you're the man today! I just pulled the humidistat out of the return and the sail switch (especially the sail itself) was caked with dust and, as you suggested, stuck in the open position. You made that suggestion more than once but I didn't catch on the first time.

    I vacuumed all the dirt/dust off the sail and now the switch is operating properly. In fact it seems the whole system is working properly now.

    Thanks to everyone who replied for your help and insight!
    Last edited: Jan 20, 2012
  13. DonL

    DonL Jack of all trades

    Messages:
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    Location:
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    No, You be the man. Glad you got it working. Terry Love is the Big Man...
  14. jgurland

    jgurland New Member

    Messages:
    6
    Location:
    Maryland
    Thanks, Don. Here's another update: After I cleaned up the sail switch it worked for a while then quit again. But I think I've got it figured out:

    There's a metal bracket that's part of the humidistat that goes into the duct and sits directly below the sail. The sail is made of a thin plastic film (reminds me of the old lollipop wrappers at the bank when I was a kid) and I guess it rubbed against that metal bracket one too many times. The film has a split in it, right at the spot where it meets the edge of the bracket. So when the air flowed, the sail was "catching the breeze" and getting pushed down like it's supposed to - but then it was getting stuck on the edge of the bracket and wasn't able to lift back up when the air turned off.

    My temporary fix was to put a narrow piece of duct tape over the slit in the sail. It's not so heavy that it will weigh down the sail and turn on the switch unnecessarily, and it will act as a buffer so the edge of the bracket will have to wear through the tape before it reaches the sail again. The sail is available as a replacement part for about $15. That's a lot cheaper than a new humidistat and/or humidifier, so I think I'll order one and hope my tape hack lasts until it comes in.

    Problem solved. Thanks again! This forum is a terrific resource and I appreciate your generosity with your time.
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