As far as I know, I have a rebranded Aprilaire 56 controller, and a rebranded Aprilaire 5?? Humidifier (the top water connection is one I've never seen in photos, so it throws me on which model).

As Trane does not allow anyone to purchase parts, or do any work themselves, and that is the total opposite of my philosophy, I figured this forum would be super helpful.

A while back, I noticed the Humidifier was non-functional. I started out by replacing the saddle valve with a higher quality ball valve, and flushed the inlet line to the valve. It is attached to the cold water line, and I do not have a heat pump. Having very hard water, I noticed the solenoid valve was totally blocked. The strainer also appears to be missing. On a test bench, the valve did not function. I disassembled and cleaned it in an Ultrasonic cleaner, to the point of dissolving the yellow chromate finish. I then reassembled and tested with an adapter I fashioned to connect to the garden hose, and with 24 VAC applied, it now functioned correctly.

I then reinstalled, and turned the dial on the model 56 to the test position. It operated correctly for about 10 seconds, and never operated again.

24 VAC comes on as it should on R & C when the furnace calls for heat or the blower operates.
The temperature sensor reads the proper resistance compared to outdoor temperature.
Solenoid resistance is 29 ohms. The relay clicks audibly when the dial is advanced to higher humidity.....but no voltage is ever present on H & H to operate the solenoid. Connecting the solenoid to R & C to test, and it functions correctly.

It would appear the control board is now bad on the model 56.

The unit only seems to be sold complete, and model 56 seems to be discontinued. The price is well over $100.

Any tips on troubleshooting the PCB, or any other creative ideas? Failing that:
A possible cheaper solution appears to be this found on Amazon, using R & C to power a relay to switch 110 VAC to operate the replacement, and power the solenoid. An appropriate enclosure could be made, and the humidity sensor could be stuck on the inside of the duct above the hole for model 56.


Aprilaire model 56

Aprilaire model 5??

https://www.amazon.ca/KKmoon-Digital...7C4QT6XY&psc=1

 

Welcome to the forums.

If you can hear the relay operating but aren't getting any power..... more than likely the relay contacts have gone bad. It shouldn't be too hard to change that relay. It should have mfg parts numbers on it. You can post them if you need help locating it. A picture works too.

 

Thanks so much Pete for the reply and the welcome!

The relay was my thought as well, but upon measuring the voltages on the relay, it was not making much sense.
I figured if the relay went bad, it would go intermittent, and not appear shorted like it seems. With readings like I got, it should be on all the time. I measured the voltage between "C" (the R & C terminals) and the relay wiper/contact points. The readings make it look more like a problem elsewhere in the board, but what do I know.
The most failure prone parts on the board in my opinion would be either the relay or the potentiometer, I would think. Do you think it is worth soldering in another 24 VDC relay? I have many in stock, just not that same form factor. Lol.

 

If you are connected to R and C...... there should always be 24vAC present.
You would normally connect from W to C so that 24vAC was only present during heating.

On that relay..... 1=NC, 2=C, 3=NO.
So 2 and 3 are the important connections.
Between C and 2 will always be the supply voltage.
Between C and 3 will be the voltage when calling for humidity.

 

What was I thinking when I wrote that! Yes of course you are absolutely correct. There is always 24 VAC present on R & C. That very convenient supply is where I perform all my experiments. Lol.

As those numbers 1,2,3 are totally arbitrary that I chose, and there is no circuit map on the relay itself identifying pins 1 to 5, it is hard to say whether 1 or 3 is NO or NC, if there is something going on inside the relay.
#2 I presume is the wiper, and should always have 24 VAC.
The coil connection was easy to spot.
What throws me is that when there is no call for humidity, both 1 & 3 have 24 VAC.

I think I will change the relay.

Earlier, I was taking voltage readings on the board, and my probe must have slipped shutting the furnace down.
Yup, I blew that $40 3.2A custom made time delay fuse.....so not having that fuse in stock, I wired a new fuse holder in parallel, with a 3.15A fuse without a time delay. Back in business, although still dry as the desert.

I learned my lesson and will only take readings with that board isolated on my test bench.

I'll let you know how it works out when I get back into it.