HUM connection not powered

I have a Carrier 9200 furnace (58MXA080-13112), and the attached humidifier is not working. I checked connections, and the humidistat is not getting any power.

The humidistat is connected to the COM and HUM contacts in the furnace. If I remove the wires from COM and HUM, the terminals have zero voltage (AC or DC).

There's a 3 amp fuse next to it, and the fuse is fine. The rest of the furnace is working just fine, and there's 24 VAC elsewhere in the furnace, so the transformer and other connections seem to be okay.

Ideas? Where does the HUM power come from? Is there a fuse or relay somewhere else I can look for?

 

Did you make your tests with a call for heat & after the fan came on? If not, try testing under those conitions.

Sometimes those terminals are not powered. It is just a switch to allow current to flow. Try checking for continuity between HUM & common. Do it first without the heat on or fan running. Repeat the test with a call for heat & after the fan comes on.

 

Your HUM terminal should supply 24vac when the gas valve is activated.

 

Got it.

The 24 VAC to the humidistat was loose and corroded. Sanded the terminals, tightened them down, and was getting steady power.

I then played with the Humidistat. Aprilaire has a nice way of measuring humidity. Seems like it was off by quite a bit, so I needed to offset the settings to compensate.

All is working. Much appreciate the help!