Humidifiers and Dehumidifiers - Aprilaire 56 Humidistat NEW and fried already

The Back Story:

When I moved into my home (it's about 10 years old) I discovered that my Aprilaire 700 humidifier was never hooked up properly. All wiring to the humidifier and outdoor temp sensor were fine. However, the wiring running from the humidistat to the furnace was never hooked up correctly. The hot wire was attached to a fuse on the furnace circuit board that was around 28V (the correct voltage) but attached to a circuit that was hot ALL the time. Meaning, if the humidifier was set to be on, the humidifier would run constantly regardless of the furnace being on.

So to correct this I hooked it up to the Humidifier jack on the furnace circuit board and then turned everything on. This ended up frying the humidistat because the voltage coming off the circuit on the furnace put out 120V instead of the 24V it was supposed to get.


The Solution
So I ordered a new Aprilaire 56 humidistat off ebay that came with a 24V transformer. I installed the humidistat per the directions EXCEPT instead of moving the switch on the humidistat from Bypass to Power (Since my unit is a 700 it should have been on Power). However, I did not have a transformer box so I hooked the humidistat to the furnace connection the same way the old humidistat had previously been connected which was on the furnace circuit board but attached to a circuit that put out 28V.

Once everything was connected and plugged in I turned on the humidistat. The humidifier turned on and started running properly for about 20 seconds and then died and some smoke came out of the humidistat. I checked all of the voltage connections again and there were 28V at the humidistat coming from the furnace and going to the humidifier.

I took the humidistat apart and could see a solder connection that was fried. I then attempted to solder it back in place and hooked it up again but this time it doesn't kick the humidifier on anymore.

So now I'm screwed and stumped. Except for having the humidistat switch on Power instead of Bypass I do not see any mistakes in the connections or cause for the unit to fry. Does anyone know if the fact it was on bypass and it would fry the unit? Anyone have any suggestions for solutions?

Yeah, if you didn't move the switch, you've fried it with being the powered unit has power.

You'll have to get a new humidistat.

How did you wire it all up?

I wanted to bring closure to this thread in case anyone else comes across it doing a search later on and looking for answers.

As I said before i ended up buying a new 56 humidistat and transformer off ebay and fried it when I missed flipping the switch to power instead of bypass. I ordered a new thermostat and hooked it up (remembered to flip the switch this time) and all is well.

I ended up mounting the transformer to the plate attached to the furnace circuit board and connected those wires to the HUM and an adjacent N on the furance circuit board via female connectors. I then screwed down the wires from the humdistat to the 24V side of the transformer. Hooked up the remaining wires and fired it up and all is well. A little bit of water leaked out the bottom of the humidifer when it first started but quickly stopped. I should probably replace the water panel but maybe i'll wait until next winter.

Anyone know of a way to clean them instead of dropping the $20 on a replacement?

$20 for the humidifier pad? Home Depot sells them half the price. They should be changed every year, and they are not made for cleaning.