Humidifiers and Dehumidifiers - Aprilaire 700 won't work

I installed an Aprilaire 700 and used the transformer that came with it. The transformer puts out about 27V (rather than the prescribed 24V). The fan doesn't work and the solenoid doesn't open in test mode or in any other setting. The humidistat is supplying 27V to the humidifier but no voltage gets to the solenoid.
I even got a second Aprilaire 700 unit and got the same result (but I didn't change the transformer).
Is the transformer bad? What else could be the problem?

Didn't change out the transformer? They are built into the unit itself.

Are you using a relay, or what are you using to control the unit to come on/off?

The transformer came as a separate unit. I didn't have a 24V accessory supply from my York Diamond 80 furnace so I needed to use the separate transformer to get a 24V supply of AC. I connected the output fromthe transformer to the RC terminals, I connected the Humidifier to the "H" terminals (with and without the current sensing relay in series) and the outdoor sensing bulb to the "ODT" terminals.
So I don't understand your statement that the transformer is built into the unit itself.

Aprilaire 700 model has it's own built in transfomer. you DO NOT need an external transformer.. The 700 is plugged into a regular 110volt wall out let.

RC on what are you connecting this to? Model of humidstat you using?

On the relay question, I am using a current sensing relay from my old humidifier (which was working fine). I tried to get the Aprilaire 700 to work with the current sensing relay in series and with the current sensing relay out of the circuitry (in case it had somehow gone bad.). My understanding is that the current sensing relay is only in place to prevent the humidifier from working when the furnace isn't calling for heat (i.e., the blower is working). T

Sorry for the misunderstanding. The humidifier is an Aprilaire 700 and I plugged that into the 110 wall outlet. The transformer that I am talking about is to provide power to the humidistat not the humidifier.

the humidistat is the Aprilaire humidistat that comes with the
Aprilaire 700. It has an outdoor sensing bulb.

sorry for the delay..

What model is the humidstat? There are a few diffrent ones out there.

I'm not sure what model number the Aprilaire humidistat is. There is no model number on it but the circuit board says B2203201 rev. B. On the back of the humidistat it says B2203202 rev. D DEFOND 0533

is your wired like any of these??

http://www.alpinehomeair.com/view.cfm?objID=C1EC4FEC-1C8E-409D-9581-3B9839F377F0

Here is the AA model humidstat.

http://www.alpinehomeair.com/related/AA%20Humidistat%20Install%20Instructions.pdf

Thanks Jay!
The red diagnostic light was on the whole time but I thought that meant the unit was powered. Instead that meant there was a problem with the wiring. The problem was the outdoor bulb was defective. When I hooked up the manual shunt the unit worked fine.
I don't know why the humidistat instructions weren't included or available on the Aprilaire website but that solved the problem.