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jrossano

Troubleshoot Aprilaire 700M Humidifier

11 posts in this topic

Hello,

 

I have an Aprilaire 700M Home humidifier that was professionally installed and worked well last winter. This winter I replaced the pad and turned it on bit it's not working. The pad had no moisture at all so i figured it was not getting any water. So I attempted the following troubleshooting. 

 
The water flowed fine to the solenoid and the screen was not clogged. The orifice and hose leading to the evaporator pad were not clogged either. When I turned the humidistat up I heard a click, but no sound at all from the solenoid valve. I tested the voltage in the wires coming from the humidistat and it read 28. So I took those wires and attached the directly to the solenoid wires. Again there was no click from the solenoid when I turned up the humidistat. So I ordered and installed a new 24v solenoid valve (#4040).
 
But here is the problem - I have the same exact symptom with the new solenoid valve! I again connected the wires from the humidistat to the solenoid and hear nothing. There is 28v coming from the humidistat, but when I connect the wires to the solenoid and measure the voltage reads .1. I don not have a 24v transformer or I’d try testing with that.
 
Does this give anyone a clue to what the problem might be?
 
Thanks,
Joe
 

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Does the fan come on when the humidifier is supposed to run?

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The simple answer is you do not have 24 volts to the solenoid .  You are reading a sort of phantom feedback without the coil hooked up. With the coil in the circuit you see 0 because you only have one side of the transformer power getting to the coil. 

 

I see on the install diagram that there may be a current sensing device to sense if the furnace blower motor is running or not.

If you have this device ,  the furnace blower must  be running to allow the power to reach the solenoid. This device may also need adjustment if it is installed .  you will find this device clipped around the black wire that goes to the furnace blower motor.  it is a simple switch that closes when current is passing thru the device. 

 

 

 

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Does the fan come on when the humidifier is supposed to run?

 

I'm not 100% sure. The fan is inside the cover and it's hard to hear anything over the furnace blower. If I had to guess I'd say it is not coming on. Does that give you more clues?

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The simple answer is you do not have 24 volts to the solenoid .  You are reading a sort of phantom feedback without the coil hooked up. With the coil in the circuit you see 0 because you only have one side of the transformer power getting to the coil. 

 

I see on the install diagram that there may be a current sensing device to sense if the furnace blower motor is running or not.

If you have this device ,  the furnace blower must  be running to allow the power to reach the solenoid. This device may also need adjustment if it is installed .  you will find this device clipped around the black wire that goes to the furnace blower motor.  it is a simple switch that closes when current is passing thru the device. 

 

It looks like the installer bypassed the blower all together. I took some pics but can't see how to include them in this reply.

 

There are two wires that are attached directly to a circuit board in the furnace. The red wire goes to the humidistat then to a connector that plugs into the cover (that houses the fan). The white wire goes go directly to the connector. That connector also has two yellow wires that exit it and go directly to the solenoid.

 

Does that mean that the water will flow whenever the furnace turns on?

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I have the same humidifier and I know that one plug connector is on the outer case and it plugs into the other connector when you close it up. I was thinking maybe it's not making proper connection or plug could be damaged.

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If your humidifier has a 110 volt plug then the power for the soloniod valve comes from within the humidfier. you said that somthing inside clicks, which means the control board inside the humidfier is trying to switch its own internal 24 volts to the soloniod. it is possible that the relay built into the control board is failed. Here is a diagram  for the internal workings of the humidfier. If the built in fan is not running then the control board needs to be replaced.

electronicaircleaners.com/aprilaire-4238.aspx

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I bypassed the humidistat with a jumper wire and the original solenoid worked fine. So I ordered and installed a new humidistat and all is working again. I even got to return the new solenoid valve for a refund!

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The simple answer is you do not have 24 volts to the solenoid .  You are reading a sort of phantom feedback without the coil hooked up.

 

I wonder if a true RMS meter would have helped here; presuming our friend was using a $5 Harbor Freight thingie.

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No, it all comes down to testing correctly. A crap ass meter will do fine for simple tests like this, but you have to test at the correct points. Even my newer guys in the field get confused about how to test (correctly) for 24 volts. 

 

The most important thing to remember when testing for 24 volts is to NEVER test to ground. YOu must test to the transformer common side. 

Same thing goes for high voltage 240 volt . Never test to ground . it is always line to line. anything else means nothing. 

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