Piss poor design of Air Vent Inc "Enviro-Stat" attic vent sold at home stores.

[1sciguy]

Bought the latest and greatest powered attic ventilation fan from Air Vent Inc.  Paid an extra $60 for their "high efficiency variable speed" model.  Fan is microprocessor controlled and vents the attic based on temperature and humidity.  Install is simple enough, cut a hole in your roof, wire it up and it automatically runs.  Seemed great at first.  I finished my install in the afternoon in Charleston SC and it turned on and ran at a nice controlled speed to vent the heat buildup.  As the temperature dropped, the fan slowed and eventually stopped.

Day 2.  Woke up at 5am because I heard what appeared to be a freight train.  Strange, because there are no train tracks on my island.  It was that damned air vent.  There was a fog outside and it set off the humidity sensor.  This, of course, draws in more cold damp air and the fan wants to run even faster.  The damn thing went to full speed and was never going to stop on its own.  It would continue to draw cold moist air into my attic.  I turned it off and since I had already cut the hole in my roof there was no way I can remove it an return it.  Removed the motor because everything is built into the motor.  The motor has a small humidity/ temperature sensor sticking out the side.

Day 3.  Called Air Vent Inc.  Let me tell you, the representative on the phone was about a rude as I have ever heard.  Bottom line, they had no engineer that they could let me talk to.  I simply wanted to know if the sensor they used was a digital sensor with I2C communication or was it an analog sensor.  If analog, I would have cut the humidity signal wire.

Today I looked up the patent number written on the motor and found out it is made by McMillan Electric in Wisconson.  Called them and spoke to an engineer.  Engineer confirmed it was an I2C chip, so there is no way to disable "only" the humidity function. 

Anybody have any great ideas about coating a humidity sensor?  Dry it out and then apply a varnish or hot glue?  Maybe put it in another tube with a desiccant inside?  If I can't disable the humidity function of the fan, I will have to add a second thermostat so the power to the entire fan is only present when the attic is over 80 degrees.

[fixy88]

I'd be hesitant to coat it directly - I would just seal it in a small air space somehow when the humidity is low, or as you say add some desiccant to the air space you seal it in.

[SilverSolder]

If it is an I2C sensor, you may be able to use a shielded cable of some kind and move the sensor to a better location?

It seems reasonable enough that if moisture is detected in the attic, the fan should keep going?  We just don't want it to get triggered by the weather outside, if the attic itself is dry -  right?