Aprilaire 600, Humidistat Doesn't Sense Correct Humidity

I had an Aprilaire 600 w/ Humidistat Model 60 installed in my crawl space by a reputable company about a month ago. It did not work correctly as my in-house humidity increased very little. Eventually, after researching everything, I found that they installed it incorrectly. They placed the humidistat right beside the humidifier on the return. The humidistat was sensing the humidity coming from the humidifier. This was causing it to think there was more humidity in the house than there really was.

They came back out to look at the problem. Unfortunately, my return is not big enough for them to install the humidistat anywhere else on there. Instead, they went about 5 feet up the return line. They cut the duct work, installed a metal box, reattached the duct work to the metal box, and installed the humidistat on the metal box. This allowed the humidistat to be upstream from the humidifier as advised in the installation instructions.

With this new configuration, the humidifier is still not working right. I have 2 hygrometers that measure humidity within 2 points of one another. I have found that when I place the hygrometer in the crawl space next to the humidistat, both register nearly the same humidity. The problem is that inside the house, the humidity is usually much lower than the crawl space. For example, both the Aprilaire humidistat and my hygrometer located in the crawl space measure 42 as the humidity. Yet, in the house, the same hygrometer measures 30 for the humidity. It would seem that the Aprilaire humidistat is sensing the humidity in the crawl space instead of the humidity in the house. Does anyone have advice on where to go from here???

Thanks so much,
Lee

 

With a crawlspace installation..... the humidistat should be located inside the house.