Replacing Aprilaire 760 with 700M--wiring question

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Old 03-03-14, 09:59 AM
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Replacing Aprilaire 760 with 700M--wiring question

My new Aprilaire model 700M humidifier wiring calls for the control unit to be wired through a transformer. My old model 760 had the both of the control's wires connected to the two brown wires on the humidifier (despite the fact that the wiring diagram called for connection to a 24v terminal on the furnace). The line cord on the 760 was plugged into an outlet mounted on the furnace that is live only when the furnace is running.

Can I connect the 700M the same way? Does the new controller require 24V power? If so, can I simply use the old controller? Thanks.
 
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Old 03-04-14, 01:37 PM
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Yes, the new 700m you'll need the to supply power to it since the 760 had it's own transformer.

You can reuse the old humidistat.
 
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Old 03-04-14, 03:42 PM
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Thanks. Is the 24V lead just needed for the solenoid valve? The old humidistat simply functioned as open or closed, with no electrical connection. And, since the 760 was plugged into an outlet that is live only when the furnace is running, do I need to plug the 700M into an always-live outlet?
 
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Old 03-04-14, 05:49 PM
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The 700M gets plugged into an always live circuit. The 24vac that operates the solenoid valve needs to be switched. Possibly your furnace has HUM terminals..... otherwise the transformer will need to be switched.

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Question for Jay..... the instructions say not to connect the transformer to the blower circuit. Why is that ? Is it simply so that the humidifier doesn't operate in the A/C mode ?
 
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Old 03-06-14, 05:36 AM
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Question for Jay..... the instructions say not to connect the transformer to the blower circuit. Why is that ? Is it simply so that the humidifier doesn't operate in the A/C mode ?
I really don't know for sure what the real reason for this. There's a couple of things that come to my mind. One of as you said, to avoid running it when the A/C is running, or some larger fan has more power draw or surge, and want to prevent from hurting the humidifier, or if the person does a poor piggy back of the wire hook up, it may start a fire on the wire connections.
 
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Old 03-12-14, 02:25 PM
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FYI, I checked with Aprilaire and they said that as the blower starts it can cause unwanted spikes in power that could damage anything else wired into the same circuit.
 
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Old 03-25-14, 11:26 AM
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Rapidly clicking thermostat

I recently did this exact same thing. My old furnace was replaced with a Goodman FHA furnace, and I noticed the Aprilaire 760M was no longer working. After receiving a quote of $700 to replace the humidifier, I decided to do it myself. Dropping in the physical unit - the 700M - was a piece of cake. It's the wiring where I have the issue.

Looking at the wiring diagram of the furnace, and consulting the owners manual tells me that I should connect the 24VAC humidifier to the Common Connection of the control board and the Yellow wire off of the ID Blower Pressure switch. I was to use a jumper wire with a piggyback connector to tap off of the ID Blower switch. I verified I was indeed getting switched 24VAC between those two points, so I completed the wiring in this fashion.

The humidifier now seems to work. However the issue I now have is that when the furnace kicks on - especially in the early morning when it is coming up from its cold setting - the thermostat rapidly clicks on and off as many as 10 to 20 times before finally settling down and staying on. Initially this sounds like a thermostat problem, but it seems too coincidental with the humidifier work not to have been caused by that.

Any troubleshooting ideas would be much appreciated.
 
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Old 03-25-14, 07:19 PM
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I couldn't find a listing on Goodman FHA. What's the full model number ?

In the mean time..... don't leave that connected to your thermostat as it may damage it.
 
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Old 03-25-14, 07:46 PM
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Sorry - FHA = Forced Hot Air - it wasn't meant to imply a model number.

In any event, the owners manual lists several model numbers: MH95/GCH95/GME95/GCH9.

Just to be clear, I've not added any transformer or anything that produces a voltage. I've connected the humidifier 24V Solenoid in series with the humidistat between the common connector on the controller board and the yellow wire coming from the ID Blower Pressure Switch.
 
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Old 03-25-14, 08:37 PM
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Yes.... the manual covers several models. I need a specific model number as the wiring and control boards are different between units. The model number can be found by removing the burner access door. The ID plate will be on the side wall near the burner.
 
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Old 03-25-14, 08:44 PM
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The full model number, according to the sticker, is GMH950703BXAG
 
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Old 03-27-14, 07:57 AM
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A little more information, My thermostat is a Honeywell Chronotherm III circa 1990. When coming up from the overnight cool period, it utilizes an algorithm that they call (I believe) "Adaptive Recovery". They don't really describe it too well in the owner's manual, but it sounds like a PID-like algorithm where they turn the furnace on and off in an effort to be more efficient and to not overshoot the target temperature.

This morning, the thermostat started its clicking about 30 minutes before the end of the cool period. I manually raised the target temperature by 1 degree which basically defeated the "adaptive recovery". The thermostat stopped clicking immediately and hasn't misbehaved since. Tonight before bed, I am going to open up the thermostat and set it for conventional recovery to see how we fare in the morning.
 
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Old 04-02-14, 10:07 AM
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Still clicking

after a few days of not clicking with the thermostat set to conventional recovery, it started clicking again. So for the moment, the humidifier has been disconnected.

I have two other of the same thermostat in my house, and the top part separates from the base. I was thinking about swapping the tops from one of the other thermostats to see if the problem stays on the same zone, or moves with the thermostat.

Any words of advice yet based on the model number I provided above?
 
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Old 04-04-14, 04:47 PM
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On some Goodman units they give you the 24vac connection point and a 120v connection point. Your furnace has only the 24vac point. I don't think your thermostat can handle the added load of the humidifier.

That leaves you with two choices.... use a relay at the furnace to switch the 24vac to the humidifier or use a 120vac - 24vac transformer and connect it to the 120vac EAC (electronic air cleaner) ports. Actually a third choice would be to replace the thermostat.

You could try swapping the thermostat but I think you'll have the same problem demonstrating that the t'stat can't handle the load of the humidifier.

Let me know which way you want to proceed.
 
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Old 04-04-14, 06:29 PM
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Thank you. I was thinking along those lines myself.

The humidifier came with a 120-24 volt transformer. I could wire the humidistat and current-sensing relay in series with the humidifier and this transformer. This would totally remove the humidifier from the thermostat circuit. I always think of the current sensing relays as a sort of kludge, but I guess if it works.....
 
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Old 04-08-14, 07:37 AM
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It was the thermostat after all

An update to the saga. I re-wired the humidifier circuit as I described in the last posting. I am tapping off of a 120V circuit with a 24V transformer. This then forms a circuit with the humidifer solenoid, humidistat, and current sensing relay all in series. The humidifier works beautifully and reliably.

The only problem - the thermostat still clicks. So this time I did what I said I was going to do - I switched the thermostat head with another from a different zone. I was wondering how long I was going to have to wait to see some symptoms, but the very next morning - the same thermostat head started clicking in its new location. In my mind this is proof positive that it is the thermostat that is broken.
 
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