Aprilaire dehumidifier 500A not working but test does

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Chad s

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so I have an Aprilaire dehumidifier 500A connect to an automatic aprilaire control. The system is 6 years old. The control is the one shows the digital humidity, has the blue light and the knob to adjust the humidity level 0-7 plus a test / reset at 8. The control is getting power as it's lit blue and has a humidity reading on the display but any setting from 1-7 won't call for water. Although it does turn the water on if I set it to test/reset at #8. I initially though solenoid but didn't think that would be it if it opens on the teat setting. Any advise? Thanks
 

Reach4

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Make sure there is 24VAC voltage between "W/G" and the Cf terminals when the burner is running. A broken wire could cause your symptom. That seems unlikely, but it would be worth checking.

There is a setting to make the 500A ignore the external sensor. I don't find the directions on how to put the unit into that mode right now. I have my 500A in that mode currently. I am thinking that measuring the voltage across the ODT terminals could be used to see if that sensor is working, but I don't know what would be normal.

What does your humidity reading say?

If you can find your humidistat manual, see what it takes to put the unit into manual mode. I think older models had you put a resistor across the ODT terminals, but mine involves using a switch, and then cycling the furnace power. http://www.aprilairepartners.com/do...al-humidifier-control-installation-manual.pdf page 14 shows the Auto/Manual mode switch.
 
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Dana

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The 500A is a humidifier, not a dehumdifier- it can only add, not remove moisture from the air.

In most homes the best thing to do would be to decommission or completely remove the humidifer, since raising the humidity raises the risk of mold and rot in the structural wood closer to the exterior of the insulating layers. During the winter the colder wood takes on moisture as adsorb, then releases it in spring, raising the humidity inside walls. If the drying rate can't keep up when it's still cool out, as the temperatures rise into the high mold growth temperatures springtime mold spore counts soar.

If the house suffers from chronically dry winter air (<30% relative humidity @ 70F for weeks on end) it's a symptom of excessive air infiltration from air leaks in the exterior surfaces of the house, or excessive mechanical ventilation. The better treatment of that symptom is to seal up the air leaks. All homes occupied by breathing, bathing, cooking humans have ample interior moisture sources, and during the winter the humidity levels can be controlled by the ventilation rate, provided the house is sufficiently air tight. Sealing up the leaks also prevents excess adsorb and condensation along the exfiltration paths. (Large air leaks in the upper floor ceiling can sometimes be found by the wet insulation or mold growth patterns on the underside of the roof deck.)

In colder climates (US DOE climate zone 5 or higher) the humidity should be constrained to no more than 40% RH @ 70F during the coldest 12 weeks of winter, 30-35% would be even better. At 30% it is humid enough to prevent the dry throat dry skin fingernail splitting discomfort issues, without a significantly increased risk of airborne virus transmission. Health professional recommendations for human health and comfort are to keep it between 30-50% RH, but it's healthier for the house to keep it at the low end of that range when it's cold outside.

The dew point of 30% RH/70F air is about 38F, so any time the sheathing & siding is colder than 38F there would be a water vapor pressure through the wall. But 50% RH/70F air has a dew point of about 51F, which means a much bigger vapor pressure difference during the coldest weeks, and a much longer moisture accumulation season, for higher peak moisture in the wood, and higher moisture content when temps hit the 60s & higher outside when mold blooms can really soar quickly.

So...


...if you're still planning to fix the thing and run it, get a few cheap (~$10) AccuRite humidity monitors and track the humidity in a few locations in the house, and back off the humidity setting if it's bumping north of 35% @ 70F in mid winter.
 

Jadnashua

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If the thing was designed with an outdoor reset, it won't allow the humidifier to turn on if it senses it's 50-degrees or higher. If it does have one, and the sensor is bad, it might not ever allow it to turn on.
 
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