Aprilaire 700m humidifier not working

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Old 02-15-15, 02:02 PM
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Aprilaire 700m humidifier not working

Hello all!

Hoping I could get a little assistance here... new-ish homeowner who is somewhat capable but totally inexperienced in HVAC.

This winter, the air in my house has gotten so dry that I literally wake up at night with nose and throat almost in pain from dryness. The brutal cold this year has not helped, I'm sure, but it definitely wasn't like this last winter. This led me to check the humidifier on my return duct, and voila... it appears it isn't functioning at all. It was working last year, and I changed the water filter on it last year and it definitely showed signs of use. I took a look at it last week and it is basically like new... no sign of water flowing or any buildup. I turned the blower fan to "on", and found there was no water flow or signs of the fan working.

The humidifier is an Aprilaire 700M... which is the reason I've had to go to the forums. I'm not finding anything on what I gather is the "manual" (700M) model. I have turned up the settings to max with the blower on, and still nothing - no click from the solenoid and no fan/water flow.

I put a multimeter to the contacts coming off the humidistat, and got a small voltage measurement coming off it, however that was regardless of whether it was set to off or not. I am not convinced that it is the manual humidistat, since it seems to be a relatively simple piece of the puzzle and I don't know what could have caused an issue with it. Anyone have any ideas on where I can start troubleshooting this thing? I cannot seem to find any resources for this particular "manual" model. Thanks!
 
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Old 02-15-15, 02:06 PM
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Welcome to the forums.

There are several versions of the Aprilaire 700.


OLDER APRILAIRE 700'S HAVE THEIR OWN INTERNAL TRANSFORMER AND REQUIRE A SWITCH CLOSURE ONLY. THIS USUALLY PERTAINS TO ALMOND HOUSING UNITS…. PRE OCTOBER 2007.

 
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Old 02-15-15, 02:10 PM
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It does indeed, and it is plugged in and turned on
 
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Old 02-15-15, 02:14 PM
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I have this model. While your furnace is running, move the dial t the test mode on the far right. You should hear an audible click of the solenoid opening up. If no water starts running through in 30 seconds, maybe your water line is clogged?

The max setting for this model used to be 7 (from the dial) but if you move it ever so slightly... you can make it an 8.

The test mode will only run for 2 minutes, then shut off.
 
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Old 02-15-15, 02:18 PM
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Actually, now that I am thinking about it... I have to admit a possible personal guilt.

My assumption is that the humidifier is somehow wired to the blower motor, as it only comes on when the motor is running (theoretically). I also did some self-diagnosing and heater repair at the end of last year, which actually turned out to be successful through a probable miracle. I was messing around in the confines of the heater, trying to find a sensor that had tripped causing the heat to not work. Somehow I did manage to fix it, however now it occurs to me that in re-assembly I may have not reconnected whatever wiring went to the humidifier. I am about to head down and crack the thing open and see it there are red-flag disconnected wires inside that I failed to reconnect! Any idea on where the wires would run to? Heater is a payne heater.
 
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Old 02-15-15, 02:22 PM
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I had indeed looked for the "test mode" option, as I found that on other sites, however my humidistat does not have it. The dial itself just goes from "off" to "45" with no sign of a test mode. Seems like I managed to get a pretty simple version of what is sold nowadays! There is nothing on the humidistat except the dial to change the humidity level.
 
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Old 02-15-15, 02:22 PM
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The 700 is the type of humidifier. M= manual humidistat and A= automatic thermostat.... usually with a light up display.

Like I mentioned.... there are two sub models of the Aprilaire 700 and they are wired differently.

Here's something you can try. There are two wires coming out of the humidifier. Disconnect them from the external wiring and connect together. See if that turns on the humidifier.
 
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Old 02-15-15, 02:34 PM
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hey hey good idea. ill try it now.
 
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Old 02-15-15, 02:41 PM
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OK, I gave that idea a shot. Disconnected the two wires leaving the humidifier and connected them together, plugged it in, and nada. Not a thing. I assume by doing that I was taking all the switches out of the picture and just hardwiring it to be on when recieving power, correct? Thats a bad sign!
 
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Old 02-15-15, 02:48 PM
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Like I've mentioned several times... there are two differently wired 700 models. Either yours requires the 24vac to be sent in to it for activation or the unit requires an external switch and is defective.

Tell me where the control wiring connects.
 
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Old 02-15-15, 02:57 PM
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Following the wiring back, there are two wires coming off the manual humidistat that run to the two coming out of the bottom of the humidifier, and they are connected to another two wires coming off the board in the heater. I just cracked open the heater, and all the wires that involve the connection to the humidifer are wires that I never would have touched or disconnected in my previously mentioned repair job on the heater. So it would appear that that heater repair did not change anything respective to the humidifier.

Pulling off the cover of the humidifier, it seems the two wires coming off the solenoid and the two connected to the humidistat/heater connect to the back of the fan on the humidifer cover via a plastic four-pin connecter. To ensure that four-pin connection wasnt the issue, I removed it from the plastic housing on the cover and plugged it in solidly while the blower was running... and nothing. I have previously disassembled the humidifier cover/fan, and see that everything appears to be running into a relay on the back of the humidifier fan motor. It does not have a particular "control board" that I can see, just a large black relay that seems to handle everything
 
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Old 02-15-15, 03:08 PM
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And in response to your previous mention about the internal transformer - that is probably the model I have. I am no electrician, however it does say on the side that the solenoid requires 24v AC, which I assume is being stepped down inside the humidifier cover.
 
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Old 02-15-15, 03:09 PM
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sorry about that, PJMax, glad you caught the distinction between the Manual one and the Automatic, which I have.

Just a thought... but you are sure the water supply is good, right?

I currently have my own model hooked up to come when heat is called for, others choose to have it run (when needed) when hooked up to the fan. Both options have their merits.
 
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Old 02-15-15, 03:15 PM
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Yeah, theres no problem with the water supply as far as I know... but I'm getting no fan action either. It appears nothing at all is working, which leads me to an issue with the device itself. If I could figure out which part, I'd just order the part itself, however without troubleshooting it I worry that I'll replace something that works fine!
 
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Old 02-15-15, 05:46 PM
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@captain.... the 700 is a confusing model due to the design changes from old to new. I once told a member to wire it incorrectly before I became aware of the differences. I won't do that again.

Ok.... It would appear that your humidifier is of the newer style and follows the diagram below. That means when you supply 24vac to the brown wires of the humidifier...... a relay clicks inside the unit, the fan starts and the solenoid opens.

Name:  700M.jpg
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I'm going to need to know where the two wires connect inside at the control board. One should be on C.
 
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Old 02-16-15, 11:08 AM
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PJMax... I truly appreciate your experience and help in this project... however I find this morning that I can't properly repair my humidifier. Have to love the northeast... my pipes have frozen at the main coming into the house. If I fix it now, I wont know. On to my next project... unfreezing my pipes so I can take a shower! I'll let you know where they are connecting as soon as humanly possible. Thank you very much for your help up until now! I'll be back after I thaw my house out from this godforsaken weather!
 
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Old 02-16-15, 04:17 PM
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I'm just north of you getting the same crap.
 
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Old 02-20-15, 11:32 AM
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OK! Thawed water pipes and no breaks... thank god. I am looking at the relay now... there are six connections, and here is how it is connected:

BLU (4) | WHT (6)| YLW/BRO (8)
BLU (3) | BLK (5) | YLW/BRO (7)

When I pull the wires off the connection, I can see a small number at the base of it, which is in parentheses above. It appears (1) and (2) are not used, and there is no post to attach wires to on that slot. Each yellow and brown are both spliced together and on the same post.
 
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Old 02-20-15, 11:52 AM
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Bah, I just re-read your post. Did you mean where it connects to on the heater's control board? Previous post was regarding the relay inside the humidifier. Ill crack open the heater and check for you
 
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Old 02-20-15, 12:41 PM
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Image of Control Board

Name:  Heater control board - Small.jpg
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The white wire is attached to the second screw down in the set of screws on the left, and the red is attached to the "24vac humidifier" port at the bottom. I'm thinking of wiring out the humidistat to test if that's the issue!
 
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Old 02-20-15, 12:56 PM
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Hah unfortunately I'm talking to myself on here... but if anyone happens to look this over in the next few minutes, I am considering shorting the wires to the humidistat to remove that switch from the process. I cant find any reason not to, as it seems it is not stepping down the voltage for any reason and it will eliminate a possible problem in the system. Can anyone see a reason not to wire it out? I don't believe it is stepping down the voltage or offering resistance in any way... but I honestly dont know much about this. If anyone sees a red flag in this, let me know!
 
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Old 02-20-15, 02:14 PM
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Eureka! Wiring out the humidistat worked. Guess tharrs my problem! Guess I'll order a new manual humidistat.

Anyone know if there's any short-term danger in just leaving it hooked up to run while the fan is on, with no humidistat? Because I'll be honest... I'd just as soon make it a rainforest in here rather than continue to deal with the dry mouth/nose/skin. I guess I can unplug it when water starts running down the windows! Thanks!
 
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