Attic fan thermostat: Off when should be on

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Old 05-26-18, 09:23 AM
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Question Attic fan thermostat: Off when should be on

My attic fan motor quit, so I replace it. After wiring everything back, the thermostat turns the fan ON when the attic temperature is below the setting, and OFF when the attic temperature is above the setting.

For example: Attic temp: 90 degrees.
Thermostat setting from 50 - 90 degrees, the fan runs
Thermostat setting from 90 -120 degrees, the fan is off

Shouldn't that be the other way around?

BTW, I replaced that thermostat with a new one from Lowes (Air Vent Inc), it behaved the same way.


-Jeff
 
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Old 05-26-18, 09:32 AM
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Yes, it should be the other way around. The fan should be on when it's hot and/or humid and off when it's cool and dry. It sounds like you have something wired incorrectly. Often switches have a normally open and a normally closed contact so it might be as simple as moving one wire.
 
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Old 05-26-18, 10:05 AM
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The Air Vent thermostats show as a single purpose switch with two wires that you connect to.
They also offer a humidistat in the same package.
Sounds like you may have a humidistat.
 
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Old 05-26-18, 11:31 AM
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@Pilot: I just tried switching the only two wires I know to switch and it behaves the same.
Wiring:
Ground to box.
White cord from power to white cord on fan motor.
For Black wires: there are two combinations regarding the switch. I tried both. Both behaved the same (I figured they would).

@PJ: I don't see anything in the documentation about humidistat.
 
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Old 05-26-18, 02:28 PM
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Is there a part number on it ?
I can't find any control that has a three wire switch.
 
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Old 05-29-18, 06:17 PM
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@PJ, sorry for the late reply, I do appreciate your help (Went backpacking this weekend).

Here's the one i have currently:
https://www.amazon.com/dp/B002TYK4A6...a-308511235610

Here's a version of the one I tried from Lowe's (which i just returned):
https://www.lowes.com/pd/Air-Vent-Po...kaAvUxEALw_wcB
 
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Old 05-29-18, 07:28 PM
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Those both work the same exact way. The one from amazon has a firestat that burns open at a high temperature to shut the fan down in case of a fire.

The setting on the front is the TURN ON temperature.
Set between 90-100 and forget about it.
The lower you set it the longer it will run at night.... keep that in mind if noise is an issue.
 
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