Solenoid won't open--voltage drops when connected to humidistat
Our Aprilaire 600 humidifier's solenoid doesn't open, so no water ever goes through. I think I've isolated the problem to the solenoid itself. The humidistat is providing the right voltage to the solenoid when the heater is on and blowing heat (I verified this by disconnecting the humidistat's wires from the yellow solenoid wires and used a multimeter--showed 24V). But when I connect the wires back to the solenoid, and go through the same process, it only shows 0.1V, and the solenoid doesn't click or open. So it seems the solenoid is messing with the voltage?
My humidistat is set to manual, and I've verified the voltage as well at the humidistat H terminals and found the same results (24V when not connected to the solenoid and heater on, 0.1V when connected and heater on). On a side note, the humidistat clicks but the solenoid never does.
Any ideas what to test next? Everything else in the chain is working (checked filter, saddle valve, and blew through top part to make sure there were no obstructions--there weren't).
Re: Solenoid won't open--voltage drops when connected to...
The coil may shorting out the 24vac supply to the solenoid. Recommend replacing soleniod.
Normally you should be able to read the 24vac across the solenoid when energized.
The other option is to get a 120vac to 24vac transformer and test the solenoid. This way you will know if the solenoid is the cause or the 24vac source is the problem.
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Check to see if you are getting 24 volts from the transformer, if not, turn off power to the transformer and check the resistance of the secondary side, if no resistance the transformer is bad and need to be replaced. Also check to make sure all the wires are secure. If you are getting voltage at the transformer then bring power directly from transformer directly to solenoid valve and it should click open and let the water through, if it does then either the sailswitch/current sensing relay is bad or humidistat is bad.
Disconnect the water line to the inlet water valve (the solenoid), catch any excess water or drips in a small container
Turn the water back on slowly and see if water flows through the open line (the one you just disconnected - catch the water in a small bucket)
If you have water to the valve, it's probably the solenoid valve - you can test this by reconnecting the water line and turning the humidistat all the way up. You should hear a click as the solenoid tries to open. If it clicks and no water comes out it's the valve. If there is no water to the valve, you'll need to detrmine the reason(s). Sometimes the small line tap valves commonly used with humidifiers can plug up or malfunction. If you try to repair or replace the tap valve, make sure the water is turned off.
If no click, it could be the humidistat or there is no power to the unit.
If the humidistat is bad, you won't hear any click and no power will be sent to the solenoid valve. In that case, the humidistat may be defective.
Depending on your comfort level and knowledge, you can try applying power directly to the valve by bypassing the humidistat, but only try this if you are comfortable working with electricity. The voltage should be around 24 volts (in the USA) , which is low, but requires some knowledge.
These units have simple configurations They have a water supply similar to a ice making referigerator, an enclosure connected to your supply duct that houses a prop fan and media, a seperate humidistat and a drain for excess water. Your unit may also include fancy controls including an outside thermometer & humidistat to avoid over humidification that can cause problems during freezing weather. The humidistat looks a lot like a thermostat and is located in your living space or in the return duct. The prop fan in the box pulls air from the duct, through evaporation media and back to the duct. An electric solenoid valve releases water that pours over the media.
If the humidiy is below the humidistat seting and the AC/heater is running, the Aprilaire fan starts and the solenoid valve opens. I suspect the facier controls include the flashing warning light.
The warning light spells problem. Aprilaire's customer service should be able to provide guidance for the homeowner in the form of simple checks. I suspect your contractor is avoiding a warentee call and the trip it requires.
A word of caution. These humidifiers can be powered directly from your air conditioning unit control board from an auxiliary connection. If the control board isn't rated to carry the current required by the Aprilaire fan, valve and controls or the Aprilaire encounters and electrical problem, the board can be damaged. This can be avoided by using a relay. The AC board switches a low energy relay. 120 volt house power is connected to load side of the relay and runs the Aprilaire.
My board cooked at a location near this connection, but I can't be sure that the load from the humidifier caused it since four of our neighbors also lost their board. It failed the evening of a snow storm and required a costly emergency after hours service call. The next day a new board required a three hour drive. Fortunately a fan powered propane heater kept our pipes from freezing.
Your solenoid may have seized. The best way to check is remove the cover off the humidifier pad housing, remove the rubber tube of the distribution tray and see if water comes out while in the test mode. If you have a volt meter you can test to see if you have 24volts at the two wires connected to the solenoid. If you have 24volts there but no water ,the solenoid is bad if not you may have a bad humidistat or humidifier transformer depending on how it is wired.
There are 3 things to check on the humidifier.
Check the metal mesh screen, is it wet after the humidistat is call? If it is dry the water solenoid my not be opening or the nozzle is plugged. The circulating fan blows air through the wet screen to add humidity. Does the fan spin when the humidistat is calling? There is an intake and exhaust on the humidifier. Check that the metal was cut out properly when the humidifier was installed to allow air to feely circulate?