Aprilaire 600 solenoid valve won't open - has voltage!

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Old 10-30-13, 02:08 PM
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Aprilaire 600 solenoid valve won't open - has voltage!

Hi all -

I have an Aprilaire 600 humidifier, about 5 years old, with the manual humidistat. Started using the heat the other day, noticed the panel wasn't getting water. Also noticed that the humidistat was clicking on, but the solenoid valve wasn't.

I removed the valve, cleaned out the strainer and orifice- no scale to speak of. Put it back. Same problem.

After doing a little reading here and elsewhere, checked some things & found that the leads to the valve were getting 24v when the humidistat is turned high enough for it to click on. Figured it was a bad valve. Bought a new one, installed it. Same problem!

When I touch both valve's leads (carefully!) to the 24v transformer in the furnace, they click.

So now I'm at a dead end. Even though the leads to the valve are getting 24v, the valve won't open when connected to those leads, but it WILL open when touched to the transformer's terminals!

Any help would be appreciated!

Thanks
 

Last edited by joeb222; 10-30-13 at 02:41 PM.
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Old 10-30-13, 08:29 PM
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Welcome to the forums.

Measure the voltage at the transformer.

Now reconnect the solenoid to your wiring and check the voltage (at the solenoid) while it's connected. The two should be very close.

If not.... what are you using for a humidistat ?
 
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Old 10-31-13, 08:15 AM
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Voltage measurements

Thanks! I just discovered this website yesterday and it looks great! And thanks for your answer.

Here are the measurements. While taking them I noticed what seems to be incorrect behavior (given what I've read about this.) So I added a few extra measurements:

- At the transformer:
- furnace off / furnace running: 26vac


- At the leads to the solenoid:

- Furnace not running:
- solenoid not connected:
- humidistat off: 0v
- humidistat on: 26v

- solenoid connected:
- humidistat off: 0v
- humidistat on: 0v

- Furnace running:
- solenoid connected:
- humidistat off: 0v
- humidistat on: 0v


The humidistat is an Aprilaire manual type. It has no model number on the case - the
only number behind the faceplate is 884021BS.

It looks like this:

Name:  Aprilaire 56 humidistat.jpg
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Size:  10.5 KB

Thanks again!
 
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Old 11-17-13, 03:51 PM
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Exact same problem with Aprilaire 600

Joeb222:
Hi. I have the exact same problem. I installed a new valve but it still doesn't work (it tested it directly to the transformer so I kwow the valve is good). With the valve connected, the leads at the valve show 24v when the humidistat (manual) is on and zero when off. But when the valve is connected the leads show zero and the valve will click and open for a split second only before closing. The strange thing is that the above is all true even when my furnace is turned off. This makes be suspect whatever flow or current sensor is used that should make it only run when the furnace is running.
Thanks for any tips you can provide.
Ed
 
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Old 11-17-13, 04:08 PM
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That looks like the 4655 humidistat which is nothing more than a single pole switch.

Reconnect your water valve, pull the cover off the humidistat and short the two wires. The humidifier should start running.
 
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Old 11-17-13, 05:34 PM
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Humidistat tests fine so maybe it's the blower current sensing relay?

It tested the humidistat and it is properly opening/closing the circuit. I tested the 24v feed from the dedicated transformer and sensing relay and the circuit is always closed and showing 24v. I would think this would cause the humidifier to run constantly as long at the humistat loop is closed. Why/how would this cause the valve not to open?
 
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Old 11-23-13, 09:38 AM
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Same problem with an Aprilaire 600m

Thankful I found this board.....

I have exactly the same problem with an Aprilaire 600m, 4 years old. Started it up, the solenoid wouldn't work - it didn't click on when the humidistat was set to open the circuit. Ordered a new one, installed it, same symptoms. To make sure I wasn't losing my mind I hired an HVAC pro. He found that the humidistat works and that I was getting suitable voltage at the solenoid (24V). So, he suggested sending the solenoid back for a replacement, which I did. I installed a second new solenoid this morning....exactly the same problem. I have a hard time believing that I've been shipped two dysfunctional replacements.

Forum moderator PJmax suggested shorting the wires in the humidistat get the system running (for joeb222). However, in my case I have voltage at the solenoid with the furnace is running and humidistat set high enough, so I'm not sure this would help.

Thanks in advance for any assistance (it's getting cold and my house is getting dry!).
 

Last edited by mikeinmich; 11-23-13 at 11:06 AM.
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Old 11-23-13, 04:41 PM
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I suspect the problem is with the blower sensing relay

Solenoid is good. Humidistat is good. The blower sensing relay loop (with dedicated transformer) is always show 24v which should be. Even though showing 24v if won't open the solenoid although sometimes it does for a split second. Could this be a be transformer that just can't stand up one the load of the solenoid is connected? Or is it the sensing relay? So I hooded the blower sending loop to a different transformer and got the same problems so I'm going to order a new "electronic relay model 50" and see what happens.
 
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Old 11-23-13, 09:54 PM
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A generic reply:

If you take the solenoid and connect it directly to your transformer and it works.... it's good.
Now you take it and put it at the humidifier and it doesn't work.... you have a voltage drop.

Measure the voltage at the transformer.
Now measure it at the solenoid with the solenoid connected.... it should be almost identical.
If not, you need to determine what in the chain is not allowing the full current to pass thru.
 
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Old 11-24-13, 10:00 AM
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Test results

PJmax - first, thanks for sharing your expertise with us...

I wasn't comfortable testing voltage at the electrical panel. It's kind of hard to reach and requires taking off the furnace panel that encloses the fan. But outside the furnace the wiring off the panel is joined to the wiring that goes to the humidistat. After taking off the two wire nuts, I measured about 28V with the furnace running (goes to 0 after the furnace cycles off, with the fan still running). At the solenoid, with wires attached and humidistat all the way up, 0V with the furnace running.

Now, just a few days ago, my HVAC guy (very reputable company in town) is at my furnace talking to me over the phone while I'm at work. He says he measures 24V at the solenoid, and therefore the solenoid is shot. What am I missing?

Would it be safe for me to simply cross the humidistat terminals to bypass the humidistat all together, in order to test whether or not my humidistat is working?
 
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Old 11-24-13, 01:29 PM
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Yes..... you can short the switching wires at the humidistat to determine if it's the problem.
 
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Old 11-24-13, 03:11 PM
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Up and running

That did the trick! So nice to see the water flowing again. Guess I need to replace the humidistat, and perhaps make a phone call to my friendly HVAC guy...

Thanks again PJ.....
 
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Old 11-24-13, 05:10 PM
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.............. You are welcome !
 
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Old 01-26-14, 09:24 AM
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Hooray - it works now - thanks for the tip

We have an Aprilaire 600 model with manual humidistat, and we've had the very same problems -- the solenoid wouldn't open, I've tried coiling the wire around the relay inside the furnace, tinkering with humidistat, etc., nothing worked, after repeated house calls by HVAC tech.

I saw PJ's tip about bypassing the humidistat by shorting the two wires to it, and bingo! Water is running through the unit. Looks like the manual humidistat is bad and needs to be replaced. Glad I found this forum!
 
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Old 01-26-14, 09:49 AM
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Welcome to the forums.

Glad you picked up a useful tip here.
 
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Old 01-30-14, 07:21 AM
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Having the same problem, not sure if doing it right, shortening the humidistat by just crossing the 2 wires? I hear a click when turning the dial but not getting any water. Got power to humidistat and the selonoid.
 
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Old 01-30-14, 07:28 AM
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Welcome to the forums.

Do you have a voltmeter ? Check for 24vac right at the solenoid valve.
 
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Old 03-01-14, 08:01 AM
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Similar issue. Humidifier not turning on even after replacing humidistat.

Amana HVAC, Aprilaire 600 and Aprilaire 56.

Based on the thread advice, I shorted the wires and the solenoid opened and water flowed. I have replaced the the Humidistat with like unit. Alas, I had not checked the voltage at the transformer.

I am confused tho....I have 0 volts at the transformer. Thus no voltage at the humidistat lugs but when I shorted to the humidifier lugs the solenoid opened. Also, it should be noted that I have voltage at the humidifiuer lugs of the humidstat when the humidifier is plugged into the 120vac.

I don't understand why there is voltage in one place but not the other and yet it worked. My suspicion is not the transformer but I don't want to run out and buy another part with getting some input. Any help would be appreaciated.
 
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Old 03-01-14, 09:23 AM
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Welcome to the forums.

The Aprilaire 600A or 600M I'm used to seeing does not plug into 120vac. It runs strictly on 24vac.
Possibly this is an older unit that I'm not aware off ?

Please confirm and post all of the model number and if this unit does plug directly into a receptacle.
 
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Old 03-01-14, 03:21 PM
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Sorry, it is a Model 700. There is a 120v receptacle mounted on the side of the furnace. My guess is that it powers the fan. The AC cord runs over to the humidifier unit.
 
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Old 01-14-15, 09:12 PM
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This thread will be filed away in our searchable archives. If you have a question with your humidifier... feel free to start a new thread.
 
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