I just moved into a new apartment with HVAC, and I'm looking to control the thermostat with a few Phidgets (I had already invested in that ecosystem, so I just needed a couple of relays).
Anyway, when I connect the R and G wires together with my relay, the system turns on both the fan and the compressor (the letter behind the green wire is indeed labelled G). I'm guessing this isn't normal; how would I go about troubleshooting this? I haven't had the chance to turn the Fan switch to "On" on the original thermostat to verify its operation.
Shorting the blue wire (labelled Y in the photo) and R turns on the compressor + fan as well, which is expected.
Best Answer
You're going to have to go look in the air handler, to determine how the control wiring is connected. The thermostat is nothing but a fancy switch, so it doesn't tell you much about how the system is wired.