Question about Aprilaire 700 Humidifier

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Aprilaire 700 Only works in test mode;

Installed an Aprilaire humidifier model 700 with a model 56 Humidistat Wiring is: correct, verified several times. Both Outside and inside sensors read okay. HH goes to Humidifier (24VAC when unit is plugged in) RC go to furnace W and 24 VAC common) and reads 24VAC when furnace is running, ODT go to outdoor sensor Plugged in the unit to 110 and both the Green and Red lights came on briefly then turned off. Dial set at 7 outside temp is 24F Humidifier only runs when in the test position with either outside or inside resistor and in auto or manual mode. Could the model 65 circuit board be bad? How to verify? Any assistance appreciated

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  • Grumpywun Jan 15, 2013

    I read on a post to use a hair dryer and blow on the thermostat. I did this and the humidifier worked one (1) time but has failed to come on since. The water solenoid is good and energizes and denergises. When energized water does flow and exits the drain hose. I have used the manual mode with the internal resistior and the unit still does not operate on a continuous basis. Hunidity in the house does not seem adequate (do not have a means to measure) but the house still seems dry to me. Any additional help is appreciated.

  • Grumpywun Jan 18, 2013

    Problem Solved: Thanks to all who contributed. Solution: Unit was wired correctly, and ran after using hair dryer on thermostat board. Reason humidifier would not run is: I have a high efficiecy furace and it appears that it was inducing humidity into the air from the outside intake and the condensation humidified the air satisfying the set humidity level on the humidistate.


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SOURCE: Water only runs with humidistat in test/reset mode

you need to make sure your humidity level in the house isnt higher then what your humidifier will provide at any givin outdoor temp. this chart is in the owners manual. you cant remove the wires going to the ODS or it will give an error unless you have a resistor to put in its place. Anyway if the humidifier works in test mode according to AA it works so you may have higher humidity than you think, the highest your gonna get is 45% as the temp outside drops it will allow less humidity so it doesnt cause window condinsation (property damage) here is a copy of the chart. the #s on the left are the dial setting
TABLE 2 – % Relative Humidity Guide
Outdoor Temperature (°F)
-10°F 0°F 10°F 20°F 30°F 40°F
10% 10% 10% 15% 20% 25%
2 10% 10% 15% 20% 25% 30%
3 10% 15% 20% 25% 30% 35%
4 15% 20% 25% 30% 35% 40%
5 20% 25% 30% 35% 40% 45%
6 25% 30% 35% 40% 45% 45%
7 30% 35% 40% 45% 45% 45%

Posted on Nov 29, 2009

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