AprilAire 700 old to new humidistat wiring


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Old 04-22-24, 12:35 PM
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AprilAire 700 old to new humidistat wiring

I have an AprilAire 700 humidifier about 20 years old. I want to swap out the old humidistat for a new one, but the wiring is different. The humidistat is mounted indoors on the wall of the input vent. The old humidistat (no model number) has six screws. 1 & 2 go to a red and white wire to the furnace. 3 & 4 go to a red and white to the control valve, and 5 and 6 are connected with some kind of connector (resistor?) that is marked Outdoor Temp Sensor, which I don't have.

The new humidstat Model 4655 simply has two brass screws. So is that the correct model and if so how do I map the old wiring to the two new screws on the new humidstat?

More details: With the old humidistat in place, the control valve turns on and off in test mode as it should, and works with the humidity settings as it should, but now the water continues to run through the valve, even after the thermostat shuts off the furnace. The humidifier fan shuts down as it should, but the water does not. So I figured the humidistat is shot.

Thanks,
Barry

Current humidistat

Same current humidistat holding cover above it

New Humidistat. Notice two brass screws.
 
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Old 04-22-24, 12:53 PM
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The humidifier fan shuts down as it should, but the water does not. So I figured the humidistat is shot.
No sir.
If the fan shuts off.... it's because the humidistat shut it and the water off.
If the water keeps coming out.... you have an internal valve problem.

Some valves are cleanable.... some it's easier to just replace.
Aprilaire 4040 - replacement example.
 
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Old 04-22-24, 02:24 PM
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OK, thanks for the quick reply. I will replace it. Thanks for the pointers to the new valves.
As far as the humidistat, any idea why the wiring is different?
Thanks.
 
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Old 04-22-24, 02:27 PM
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The basic humidistat just functions on actual humidity.
The automatic humidistat uses an outside sensor to assist in humidity control.

Terminals 3 and 4 go to the A700M..... correct ?
You can connect those two wires to a manual humidistat if desired.
 
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Old 04-22-24, 03:02 PM
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Yes, 3 and 4 go to the A700 (1 red, 1 white), and wires 1 and 2 come from the furnace. So can those wires be transferred to the two brass screws if the new humidistat were installed? Which would go where? Thx.
 
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Old 04-23-24, 12:42 PM
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Pete was correct. A new OEM control valve fixed the problem. The non-AprilAire valve intermittently would stick open.
 
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Old 04-23-24, 01:01 PM
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Since the connections are AC..... there is no polarity.

Good job on the repair. Thanks for letting us know how you made out.
 
 

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