I have a 13 year old Aprilaire Model 760. Even when the furnace and the humidifier are not running, the water that feeds into the humidifier is not turning off. I shut off the water supply until I figure out what, if anything, can be done.
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I think you're on the rate track. If it's ten years old the blade and.or the shaft may be worn out. Turn off the water line feeding the humidifier.Turn off the electricity to the unit. Drain the tank, open he tank cover and try spinning the blades with your hand. That way you can tell and see what its rubbing against and if it can be repaired. But, if it's 10 years old, parts may not still be available for that specific model.
Hope this solves your problem, look for the humidistat, it should be located on cold air return duct near furnace, make sure it is not set in the on position, if it is, then this is why it is staying on, please set humidistat any where from 20 to 35%, never over 40%. If the humidistat is set properly and is still running, you may have a electrical problem, humidifier circuit should only receive power(24 volts) when the indoor blower motor of furnace receives power, also if you have galvanized plumbing in your home, you may have a piece of rust or lime deposit in the humidifier solenoid valve preventing it from closing, turn water off to humidifier and disconnect water supply line entering solenoid valve inspect & clean protector screen. Good luck.
the 760 humidifier does not need a transformer wired externally. the 760 has its' own 24v transformer inside the fan compartment. this transformer will provide the power to enrgize the water solenoid as needed. it sounds like to me the additional trasnformer is hot all the time. when the furnace comes on, the unit gets power and the internal transformer is cancelling the power from the external transformer. this would explain why it quits running when the heat is on. since the external transformer is hot all time, when the heat shuts off, the solenoid is getting energized by the external transformer. to make this run correctly, you need to get rid of the external transformer. leave the humidifier high voltage wires hooked up so they are only hot when the furnace runs. if you have a humidistat that has a r and c terminal, you will need to wire these directly to the r and c on the furnace control board and move the switch inside the humidistat to "power". make sure it is not on "bypass". then wire your 2 brown wires from the humidifier to each of the "h" terminals on the humidistat. if you have a humidistat that only has 2 terminals, wire one brown wire to each of the terminals. this should allow it to run properly.
The tune up kit that I ordered arrived on Friday and I installed most of it on Friday night. While it is nice to have a new frame and the distribution panel and I think the price of the whole kit was fair considering it comes with the parts and 2 water panels, the fix was really simple.
The kit came with the water distribution tube with with a new blue orifice (Aprilaire #4232) already inserted. This orifice is in the end of the plastic tube at the solenoid end. When I removed the old water distribution tube, the old orifice was not really dark blue anymore but kind of a light blue and was deteriorating from 12 years of exposure to the chemicals in the water. What should have been a pin-hole size opening in the orifice was up to about 2mm or a little more so the orifice was letting way too much water through.
If anyone else has this leaking problem, and your orifice is several years old, I would check that first. It is a $2.75 part and may be the cause of the leak. The whole feed tube kit is only $8.75 and includes the feed tube, nozzle, orifice, ferule, compression nut, strainer so if you need to replace the orifice, I would order the whole feed tube kit for a little bit more.
It could be that the humidistat is not calling for humidity. Make sure that you have the dial turned up all the way (as far as it will go, just to test it) and that the blower on the furnace is running - if the unit is properly wired, the water will not run unless the blower on the furnace is running. This should do the trick. If not, the only other thing would be a bad humidistat. Good Luck!
You need to determine whether the problem is in the solenoid or in the furnace electronics. You could put a voltmeter on the solenoid connection to see if the furnace is still holding the solenoid open after the blower stops. This will tell you whether it is the solenoid or not.