While on the topic of wiring. I want to replace my upstairs thermostat with a WiFi supported model. Current thermostat has no C wire attached, but there are several unattached wires going up to the packaged unit on the roof (in addition to the G, R, W & Y wires). The thing is that the control board of the packaged unit doesn't have all the terminals neatly positioned next to each other, but rather spaced out over the board, and there's nothing marked C. There is a terminal marked B (GND) after the G R W & Y terminals, but that doesn't sound like it.
There are blue wires running in several places, including a few connected to a terminal on a relay switch. I don't currently have a Voltmeter to check if that runs 24V or higher, so I held off on connecting a wire from there to the thermostat.
Anyone have any insight on this, or do I just have to wait until I pick up a voltmeter to find where the 24V current is running to connect the C wire to?